91 ZR-1 Cutting Out Under Load

[GregCrowe]

Haven't had a problem with this car in years until today. The car had been sitting for awhile so I decided it was time to break it out of the garage and take it for a spin. We made a 10 mile trip and the car was perfect, even while spanking a Mustang on the highway. After sitting for 30 minutes, we hopped back in and the car immediately had a problem.

At idle, it's perfect, at highway cruise, it's perfect. At any kind of load situation, it has a stuttering, cutting out problem. The heavier the load, the worse the problem is. If you put the car in 5th gear and bog it down at like 20 mph, the car literally shakes.

I'm almost positive it's not a mechanical engine problem. It seems electrical or sensor/vacuum related. The only problem I have ever had with this car is a little 5 cent clip falling off the arm of one of the secondary intake flap solonoids. When that happened, it was just down on power.

Any ideas? I'm dreading having to take this car into the Chevy dealership with a blank check.

Edit: Forgot to add, it makes no difference whether the secondary systems are engaged with the key. Either way, it has the stuttering problem.

[tomtom72]

Hi Greg, I'm an apprentice owner so I'm not too versed on Z's yet but you mean that the car runs fine unless you lean on it?

Reading your description I was thinking how similar mine behaved when the injectors were starting to short out but mine would not run at all without me feeling & hearing & smelling the miss...load or no load.

You don't have a SES light, not even a winking SES light? You checked for codes? How are the plugs, wires, coils? Fuel pumps & regulator & filter are okay? Anything the ECM monitors or controls will yield a SES light if a malfunction happens. You don't have a scanner, like a Tech 1A, to scan the motor with? This is stupid but it didn't have a backfire? Those will blow off the MAP hose. Sorry I don't have something better to say like it's "this"! Do you have the Helm manual? Looks like you have to start at the beginning. The dealer or any shop would do the same steps in the absence of a SES light to give hints of where to start looking. You know spark? Fuel? Vacuum leaks?

ttt! One of the more knowledgable guys will see this & have something for you.
:thumbsup:
Tom

[GregCrowe]

Hi Greg, I'm an apprentice owner so I'm not too versed on Z's yet but you mean that the car runs fine unless you lean on it?

Reading your description I was thinking how similar mine behaved when the injectors were starting to short out but mine would not run at all without me feeling & hearing & smelling the miss...load or no load.

You don't have a SES light, not even a winking SES light? You checked for codes? How are the plugs, wires, coils? Fuel pumps & regulator & filter are okay? Anything the ECM monitors or controls will yield a SES light if a malfunction happens. You don't have a scanner, like a Tech 1A, to scan the motor with? This is stupid but it didn't have a backfire? Those will blow off the MAP hose. Sorry I don't have something better to say like it's "this"! Do you have the Helm manual? Looks like you have to start at the beginning. The dealer or any shop would do the same steps in the absence of a SES light to give hints of where to start looking. You know spark? Fuel? Vacuum leaks?

ttt! One of the more knowledgable guys will see this & have something for you.
:thumbsup:
Tom

No SES light, no blinking. Since it has never come on, I haven't checked for codes.

I don't have a Tech 1 but I do have an old Monitor 2000 which I have used before to find my secondary air flap solonoid not opening(showed rich on the right side bank via O2 sensor reading when WOT).

As far as I know, the plugs, wires, etc are fine. I'm not sure how to check that BOTH fuel pumps are working. That could be something to check into.

I do know that various vacuum lines can blow off from a backfire. I have had an occasional backfire upon startup. Most of my vacuum lines are zip tied on tighter because of this.

As far as the MAP hose, are both ends visable(to the map and to the plenum I'm assuming) ? or do you have to pull the plenum to see if the hose is connected?

[Tom]

Both ends of the MAP hose are accessible without pulling the plenum.

[tomtom72]

Greg, Like Tom said you can see the MAP hose at the rear of the plenum, it runs under the Fuel Regulator. There is a test procedure in the Helm for checking the pump out put pressure. I can type you a copy of the manual's procedure if you like. Oh, I don't have a Tech1A either. I have an old snap-on MT2000 with the proper GM software plug-in that I used to scan my motor.

There are two fuses, one on the regular panel and one on the stuff attached to the CDM box brkt. I'm doing this from memory so bear with me. The test is started with a KOEO test w/ a pres gauge attached at the schrader valve at the front of the right fuel rail. You can leave both fueses in & turn key on & see pressure. Should be about 50-55 psi. Then pull secondary pump fuse and repeat, should be 50 - 55 psi. Then pull primary fuse and repeat...50-55 psi. Then start motor both fueses in and pressure should be 45-50 psi, and shut down and see how fast it leaks down...I don't remember how much leak down is okay. The thing is the pumps only both run for the first little while...by the time the motor gets to "closed loop" w/no full power the secondary shuts off & remains off till the power key is turned on.

If you don't have a Helm I'll copy the exact info & post up....my recollection skills are not that good on something I don't do every day!:o

:thumbsup:
Tom

[haber rj]

Hey Greg sounds like you have the same problem that I had last year when one of my injectors was shorting out. The car would stumble and feel like the motor was coming apart if I tried to give it more gas. You can use a test light on each injector and it will tell you which one is not working good. My car worked fine until it warmed up and then it would start to act up. By all means check everything else out to be sure but I think that you will find that it is an injector especiall if they are original. I just replaced all of mine with RC 205's and my car is running better than it ever did, we put it on the dyno and it ran right out to the limiter with out missing a beat, good luck.
haber rj

[blackjack]

i guess you went through the easy stuff already..ie:fuel filter ,plug wires,etc?
blackjack

[Aurora40]

Hey, it's not something simple like the air duct collapsing under load, is it? That thing seems to get softer with time. I recently bought a new one and it was much more rigid than my original one. A dirty air filter would also contribute to the pressure differential.

[Jeffvette]

Air duct collapsing just feels liek the secondary system cuts out. Just runs out of air and stops pulling.

Map sensor hose off will cause crappy idle and lots of black smoke coming out of the tail pipe.

Fuel pumps, to test secondary pump. Pull primary fuse and start the car. Car should run until temp comes up and enters closed loop. When it hits that point the car will die.


With the description from greg, primary injectors are fubar'd Replace and stuttering will go away.

[mrand]

Ignition modules rarely go bad, but it sounds close to the same thing that my car as my ignition module was dieing. It was worse when hot. Has the plenum ever been off for porting or repainting (such that the dielectric/thermal grease may have been all wiped away)?

Good luck,

Marc

[GregCrowe]

Still trying to nail this cutting out under load problem down. This problem is something that just happened out of the blue, didn't slowly get worse. It also doesn't matter if it's bone cold or completely warmed up, same cutting out under load. Given that, does it still sound like an injector problem? I just don't see how one injector can make the whole car feel like it's falling on it's face.

One weird thing, this happed just after changing computer chips. I had been running a Rippie chip for years but it must have been a really old one because the car always idled way too high which was driving me crazy. I got the redesigned chip from GM that address that issue. I installed the GM chip the day the problem hit. Upon installing the GM chip, the car ran fine, idled correctly and I took my Sunday drive. It was later that day that the problem hit. Thinking that the chip might possibly be defective, I reinstalled the Rippie chip but the car still cut out just the same under load. It doesn't matter which chip is being used, same problem. Just thought I'd mention this. I can't image the chip change screwing something up but who knows? Anyone see any correlation?

[Jeffvette]

I can't image the chip change screwing something up but who knows? Anyone see any correlation?

Just a coincidence.

Still sticking by my statement of primary injectors are going.

[tomtom72]

Greg,

I tend to defer to Jeff.:worship: When my injectors went out to lunch it was just that quick. I don't actually know how many were bad as I never actually checked the injectors with an VOM. I used a scan tool to take the O2, block and integrator numbers. All that stuff was out of range & pointed to the injectors....that was after I checked the obvious: plugs, fuel filter, vacuum leaks, wires, fuel pump chart A7 diagnostic test...oh and every electrical connection I could reach also:o

The car was working fine...I shut it off & restarted and I had this slight miss, the more load the more miss...eventually it got so bad that I could smell a lean condition at the tail pipes and the plugs on one entire bank were not getting much fuel to ignite. Try a scan and post up the numbers and the guys that know that stuff will analyze the results and tell you what's up. They did that for me and taught me stuff that I had no clue about!:thumbsup:

:cheers:
Tom

[GregCrowe]

Thanks Tom. I will do that. As far as O2, block learn and integrator numbers, should they be at full throttle, idle, both?

Where should ZR-1 O2 numbers be at full throttle? I used to do a lot of that testing with LT-1's(should be 870-910) and TPI's (should be upper 700's to lower 800's). Wow, it's been years since I've hooked up the old Monitor 2000. I'm glad I still have it around.

[tomtom72]

Greg,

The Helm FSM has a page in the "Emissions & Drivability" section that has all the function values that a healthy system presents to the ECM. The numbers are taken at idle speed, in "closed loop" operation. When I did my scan I followed the manual's instructions and just reported (posted-up) the values I was seeing here and the members explained what the data ment.

You'll have to forgive my lack of knowledge! The last vette I had before this one had a holley & the only electronic parts on the car were the ignition system and the radio!:o

:thumbsup:
Tom

[GregCrowe]

Greg,

The Helm FSM has a page in the "Emissions & Drivability" section that has all the function values that a healthy system presents to the ECM. The numbers are taken at idle speed, in "closed loop" operation. When I did my scan I followed the manual's instructions and just reported (posted-up) the values I was seeing here and the members explained what the data ment.

You'll have to forgive my lack of knowledge! The last vette I had before this one had a holley & the only electronic parts on the car were the ignition system and the radio!:o

:thumbsup:
Tom

Tom, would it be possible to get a scan of that Helm's page with all the normal function values?

Thanks.
Greg

[tomtom72]

Greg,

You got it man! I'll start to work on that now.

:thumbsup:
Tom

e-mail sent 8/15/06

[GregCrowe]

OK guys, finally got the time to test everything this evening. I hope someone out there can make something out of these numbers as I could find nothing wrong with the car.

1st. I did fuel pressure tests. Someone before mentioned that the FP should be around 50psi key on. On my car, key on I get 35psi. Car running, I get 30-32psi. These values are with the vacuum still connected to the fuel pressure regulator. I tried the tests with removing the primary and secondary fuel pump fuses individually. Each time, the car maintained 30-32 psi with the car running. When starting the car bone cold with the primary fuel pump fuse yanked, the car did just as it should which was to run just fine until warming up and then dying as the car went closed loop and the secondary FP shutting down just as it should.

I didn't have a real fuel pressure gauge, I was using the low side guage on my A/C gauges. I had another cheapy guage lying around and hooked it up too. With it I got the same 30-35 psi as my A/C gauge was giving. Are these pressure numbers OK? They did not seem to move below 30 psi when reving the engine.

With my Monitor 2000 and the car running at 180-195 degrees, I got the following values:

O2's - L- .10 to .69 R- .10 to .74
Block Learn L- 136 R- 130
Integrator L- 127 to130 R- 128 to 130
Inj Pulse Width 3.3 to 3.5
TPS .44
MAP 9 to 10


Anybody see anything wrong? I drove the car around and had the same problem, perfect idle, perfect cruise, stumble under load.

[tomtom72]

Okay Greg I'm only an apprentice Z owner, since 12/04 & not out of my rookie time yet, but I'll take a stab & test what I might have learned.:o

The fuel pres #'s could be a little suspect as in a clogged fuel filter. The book gives way higher values. 55PSI @ idle on both pumps tested individually in the KOEO test. The idle speed fuel pressure should be no lower than 45 PSI or there abouts. Not to be forward but when was the last time the filter was changed? If the filter is done regularly then I would suspect the strainer socks in the tank might be clogged? The pressure regulator could be also the source of the consistant low fuel pressure at the fuel rail....I think??? I must go look that up & report back to you, sorry I don't remember but I'll check it.:o

The numbers from the scan look to be well within the "normal" limits defined by the FSM....TPS is a bit on the low side @ .44 but I doubt that is the source of the problem.....but I may not be correct on that statement and I'll try to look that up also.

Sorry I'm not very definitive but I'm not too secure in my abilities at my experience level.:o

:thumbsup:
Tom

[GregCrowe]

Thanks Tom. I think tonight I will get the car out of the garage, set the Monitor 2000 on record mode and see what kind of O2 numbers I get at full throttle. If they are both lean, than it's time to change the fuel filter and check out the strainer. I can't imagine how the fuel pressure regulator could cause the pressure to drop consistantly.

Actually, I did drive the car around the block last night and while it did cut out, it didn't seem as bad as it was before.

Anybody know what the O2 sensor readings should be at full throttle? I'm thinking in the .800's but not sure.

[tomtom72]

Greg,
Let me run this by you about the O2 sensor #'s. The sensors should respond to changes in the A/F ratio as adjusted by the ECM, therefore there will be no set number in mV's that appears. Near as I can figure if the mV's are not constantly varying then the sensors are getting lazy and or going out to lunch. They react or read what has already been done by the ECM to the A/F ratio via the injector pulse width changes. In short I think they either work or don't with a lazy phase prior to quiting all together.

I still don't like the low fuel PSI readings.....using the A/C gauge set not withstanding....book says 48 - 55 PSI in the KOEO test for both 1* & 2* pumps, and a 3 - 10 lb drop with the motor at idle speed as within specs. The f/f is an easy swap & might yield something, it's also the cheapest part in the fuel system!:) I know I tested my fuel PSI when I was having injector trouble and the difference between a new filter and the one that was in the car for 8K miles was dramatic, oh yea the OEM filter was still in my car when it was delivered.....a 15 yr old f/f is not my idea of good maintenance. I do it every yr along with some other stuff.

The regulator seems to either work or not, according to the FSM. Oh, the only variable is it's vacuum source....it is good or the hose is at fault. Check to see the hose is okay and that there is no fuel in the hose. Fuel in the hose is the tell tail that the regulator is kaput.

:cheers:
Tom

[GregCrowe]

I hear ya' Tom. I wouldn't be surprised if my car still has the original OEM filter. I'll definitely change that and see what it does to my pressure.

As for O2 reading, yes they change rapidly and dramatically at idle and at cruise speed. At full throttle, they go up way high and should be somewhere around .750-.900 and stay in a certain range. That's how we tell how to adjust our adjustable fuel pressure regulators at the drag strip. On tuned port injection cars(I still have one with a Lingenfelter 383) the full throttle O2 readings should be around .760-.790. On LT-1 cars, optimal readings are around .860-.910. I just can't remember what ZR-1's are supposed to be.

Using these full throttle readings is how I discovered once on my ZR-1 that a little 5 cent clip had fallen off the right side secondary flap actuator. Without that actuator opening the secondary air flaps, the O2 senser readings on the right side went wacky.

[Jeffvette]

GM uses short-term(integrator) and long-term(block-learn) fuel numbers. They are as they say, fuel maps of different time lengths. The short-term numbers will be very bumpy and jump all over the place, even at idle. This short-term map varies fuel for any reason such as a lead foot, hilly route, large load, a/c,vacuum leak, etc. It instantly adjusts with (in GM's case) above the number 128(the mean desired fuel delivery point) representing lean or adding fuel, and below 128 as rich and subtracting fuel. The block learn or long term numbers are a smoothed out picture of this fuel delivery. The same 128 number representing the optimum mean point. Above 128 and the PCM is needing to add fuel over the long term and vice-versa.

O2's - L- .10 to .69 R- .10 to .74 What is the rate of fluctuation? Slow/Fast?
Block Learn L- 136 R- 130 You are adding fuel, not that much though
Integrator L- 127 to130 R- 128 to 130
TPS .44 At idle or key in the run position should be around .54 volts


When testing injectors, remember that checking the resistence is only 1 of the things that can fail. You can have it also fail by leaking, spray and flow issues.

Consider spending the ten bucks on a fuel filter, make sure you have line wrenches for the job.

[GregCrowe]

GM uses short-term(integrator) and long-term(block-learn) fuel numbers. They are as they say, fuel maps of different time lengths. The short-term numbers will be very bumpy and jump all over the place, even at idle. This short-term map varies fuel for any reason such as a lead foot, hilly route, large load, a/c,vacuum leak, etc. It instantly adjusts with (in GM's case) above the number 128(the mean desired fuel delivery point) representing lean or adding fuel, and below 128 as rich and subtracting fuel. The block learn or long term numbers are a smoothed out picture of this fuel delivery. The same 128 number representing the optimum mean point. Above 128 and the PCM is needing to add fuel over the long term and vice-versa.

O2's - L- .10 to .69 R- .10 to .74 What is the rate of fluctuation? Slow/Fast?
Block Learn L- 136 R- 130 You are adding fuel, not that much though
Integrator L- 127 to130 R- 128 to 130
TPS .44 At idle or key in the run position should be around .54 volts


When testing injectors, remember that checking the resistence is only 1 of the things that can fail. You can have it also fail by leaking, spray and flow issues.

Consider spending the ten bucks on a fuel filter, make sure you have line wrenches for the job.

O2's at idle are fluctuating as normal, very quickly.

Trying to remember on the TPS, is the ZR1 TPS non-adjustable or the same as the TPI cars at the time that should be adjusted to .54 +/- .05 ?

[Jeffvette]

O2's at idle are fluctuating as normal, very quickly.

Trying to remember on the TPS, is the ZR1 TPS non-adjustable or the same as the TPI cars at the time that should be adjusted to .54 +/- .05 ?

It is adjustable. Takes a T-25 to undo the screws. It's auto correcting within certain limits. And .44 is not with those limits.

[GregCrowe]

Finally got a chance to work on the beast again. I pulled the fuel filter out and it had come apart, it rattled. That gave me some hope but I could still easily blow thru it. I put the new filter on and still had the same fuel pressure reading. Went out for a drive, same problem, stutters under acceleration. I recorded my O2 sensor readings and they appear to be just fine. Under full throttle acceleration the O2 readings are:

Left: .84 - .87
Right: .85 - .88

I'm now officially stumped. With the fuel filter coming apart, I wonder if a bunch of crap got into the injectors ??? When I undid the fuel lines and pulled them away from the original filter, I put a bowl under the lines to catch the fuel. The bowl got a bunch of dark particles in it. I wonder if some of that stuff made it into the injectors??? You would think however if the injectors were clogged up, the O2 readings at full throttle would go lean while stumbling.

I don't know, officially stumped now.

[cuisinartvette]

Yikes, hate chasing problems like that, hope it gets solved soon.


Jeff, I take it the setting on the TPS is supposed to be .54?
Sorry bout the hijack.

[GregCrowe]

As far as the TPS, they are not adjustable. Mine is .44V at idle and 4.4V at full throttle. You can loosen the 2 screws holding the TPS and move it just a tiny, tiny amount that doesn't even affect the numbers. This TPS does not have the adjustable slots like on earlier TPI motors.

[cuisinartvette]

As far as the TPS, they are not adjustable. Mine is .44V at idle and 4.4V at full throttle. You can loosen the 2 screws holding the TPS and move it just a tiny, tiny amount that doesn't even affect the numbers. This TPS does not have the adjustable slots like on earlier TPI motors.
Ok, I got confused...thought they had screws for adustment, but now its clear they arent. Good news actually, one less thing to worry about

[Jeffvette]

As far as the TPS, they are not adjustable. Mine is .44V at idle and 4.4V at full throttle. You can loosen the 2 screws holding the TPS and move it just a tiny, tiny amount that doesn't even affect the numbers. This TPS does not have the adjustable slots like on earlier TPI motors.

It is adjustable, it swings up and down after loosening the two screws that hold it on. The acceptable range is .46 to .62 volts at closed throttle.

[GregCrowe]

It is adjustable, it swings up and down after loosening the two screws that hold it on. The acceptable range is .46 to .62 volts at closed throttle.

Mine doesn't. It has 2 fixed screw locations with no pivot, no slots, no adjustment.

[phrogs]

you need to take off the cover

[GregCrowe]

you need to take off the cover

Take off the cover on what? There's nothing to take apart on the TPS. It's a sealed unit just like every other TPS GM has been using since about 1990.

[phrogs]

I was refering to the silver cover that covers the tps partialily and is conected to the throttle body it coveres the torx screws


Take off the cover on what? There's nothing to take apart on the TPS. It's a sealed unit just like every other TPS GM has been using since about 1990.

[Jeffvette]

Mine doesn't. It has 2 fixed screw locations with no pivot, no slots, no adjustment.

This is what it should look like. There are slots where the screw goes through. Plenty of room for adjustment

http://www.pnwzr1.net/Jeff/TPS.jpg

[GregCrowe]

This is what it should look like. There are slots where the screw goes through. Plenty of room for adjustment

http://www.pnwzr1.net/Jeff/TPS.jpg

Oh man, am I stupid. I was looking at the passenger side of the throttle body for the TPS, just like a TPI or LT-1 car. I guess that's the IAC motor is there. You're right, the TPS is just as you said but on the drivers side.

[GregCrowe]

Finally got some time to work on the car today and yanked the upper plenum and replaced the plugs and wires. This was at the advice of 2 Mercury Marine ZR-1 guys who know the cars. Car fired up perfectly afterwords but as soon as it warmed up a little........... same damn problem!!!! misfire under load. At this point I'm guessing primary injectors or computer. I'm really getting tired of this.

The car has been down for almost 4 months now and I really don't have the time to keep chasing it. Somebody convince me to find to the problem and not sell this car. At this point I'm really hating the car. I've owned it for 7 years, have put on about 1500 miles and have had to take the plenum off 4 times for various problems.

[tomtom72]

Greg,

I just want to say that your experience is not isolated. I went thru the same thing when my 1* injectors went out to lunch. The car had the same "miss" but not just under load. You could hear & feel it at idle. I learned one thing thru all the trials I've had with mine since I became a Z owner.....learn how to work on the car myself. That, and the first owner knew when to say when...he sold it before it drove him nuts.

I also hate to say this but I'm leaning to the alky getting to the injector coils and the "junk" in the F/F not helping the spray pattern on the nozzles. The only trouble is RC's are 1100 for the set...or there abouts. The GM stuff I think is more and then there are the Accels recently discovered that are like half the price of either of the previously named parts. The skinny on the accels is you need to call Mr. Haibeck & get different O-rings for the primaries to work. I did mine last year about this time and used the 205 RC, $1064.00 delivered for all 16. Registry members get a discount down to 68 ea.

Ofcourse when I pulled the plenum I changed a bunch of stuff besides the injectors. CCV box was leaking so gasket & hoses, 2* solenoid was N/G, coils & wires, vacuum hose assembly, tank, both temp sensors, 2* actuators, cleaned up the harness grounds, di-electric on all the weather tight connector gaskets, etc, etc...I was paranoid!:sign10:

I was starting to regret, or question the wisdom of my purchase...truth! The only thing is when it was done & the baby fires up....man it was all:mrgreen: again. The cash put a dent in the budget for sure but I did by a used car after all. Oh, and the punch list ain't done yet....I'm still playing catch up, and it isn't even anything fun like a P & P job or headers or anything to get me closer to the C5's & C6's I hang with on cruises! I'm one of the only antiques in our little cruise group...but I keep up!:D

I guess what I'm saying is hang in there & when you solve the problem you will feel good about what you've learned! Then when you go for a ride you'll even feel better....I know I do!
:thumbsup:
Tom

[GregCrowe]

I'm curious why you haven't sent the original injectors off for disassemble, cleaning and rebuild ? It's been many years since I've done that but when I did, it made a world of difference in TPI cars from the same time period. When they do that, they check the spray pattern and make sure the injectors are working properly.

Sounds like the easiest and least expensive thing to try now might be to order a new computer from GM. It would sure help if the car would throw a check engine light.

[Z Factor]

At this point I'm guessing primary injectors or computer. I'm really getting tired of this.

The car has been down for almost 4 months now and I really don't have the time to keep chasing it. Somebody convince me to find to the problem and not sell this car. At this point I'm really hating the car. I've owned it for 7 years, have put on about 1500 miles and have had to take the plenum off 4 times for various problems.

I hear your frustration and know you do not want to bite the bullet and go the injector route, but sorry to say that is most likely your problem.

As to not selling I can give you several reasons but here are two very good ones . First is that when your baby is running right you have a great time that cannot be matched by other cars, especially in a moderate price range (assumption on $$ :wink: ). The second reason is that if you were to try and sell it with the existing problem, you are not going to get as much for it as you would if it were in tip top shape. The bottom line is that you bought it for a reason and just need to get it running right to recapture the great feeling of owning a KOTH

:cheers:

[tomtom72]

Greg,

With out being forward I will say this. If you think about what's happening it is unlikely it is the EPROM or / and the ECM. In retrospect I fell for the same thing, ECM, so now I have a spare! Reason I say unlikely is that the few things the ECM controls but has no direct feed back control loop from are the injectors, hence no codes. The only feed back to the ECM from the injectors are the O2 sensors but they can only code if they fail. If the motor is rich or lean the only way the ECM knows is if it can read the O2 data. If the O2 data shows up on a scan and presents in a manner consistant with the expected then one must think that the O2's and the ECM are good. Therefore, the only other parts that can be questionable in the fuel system having to do directly with combustion are the injectors. Assuming the rest of the ignition system is up to snuff and the fuel pumps & regulator & F/F are okay. At least that is my simplistic understanding of the EEC system as it relates to this case.

Oh and as far as the cleaning & flow testing, I learned from the netregistry site that any efforts in that direction are mostly meet with less than satisfactory results, not worth doing seems to be the general concensus on that subject. That and the fact that before 92 the coils are not alky proof.

I have a spare ECM, and I can remove the 90 EPROM and lend it to you if you feel you want to try that as a diagnostic aid. Like I said, I fell for that 'easy out' because a mechanic said "oh those ECMs su#k, they always fail!" Soooo, now I have a spare!:sign10: I believe it is for a 91 as the 90 ECMs are NLA.

:cheers:
Tom

[GregCrowe]

I hear your frustration and know you do not want to bite the bullet and go the injector route, but sorry to say that is most likely your problem.

As to not selling I can give you several reasons but here are two very good ones . First is that when your baby is running right you have a great time that cannot be matched by other cars, especially in a moderate price range (assumption on $$ :wink: ). The second reason is that if you were to try and sell it with the existing problem, you are not going to get as much for it as you would if it were in tip top shape. The bottom line is that you bought it for a reason and just need to get it running right to recapture the great feeling of owning a KOTH

:cheers:

I hear what you're saying. However, I do have a Lingenfelter 383 Corvette and an LS-1 WS6 Trans Am that will both run circles around the ZR-1 so it's not like I'm blown away by it when it is running right.

As to the injectors, is there a reasone to change all 16 or should I just change the 8 primarys?

[tccrab]

As to the injectors, is there a reasone to change all 16 or should I just change the 8 primarys?

Greg:

I've was just at this particular crossroad just a couple of weeks ago and in the end I decided to replace all 16.
My decision was based on how many times I wanted to pull the plenum to work on fuel injectors.
Once was enough.
I went with the Accels, would have went with the RC's but didn't want to empty the savings account and the grandkids college fund.

I too had a misfire that, after all was said and done, was repaired by replacing all the fuel injectors AND the ECM. I had three primary injectors go bad and somehow they took out the associated injector drivers in the ECM with them.

Good luck!

TomC
'90ZR1 #792

[Z Factor]

As to the injectors, is there a reasone to change all 16 or should I just change the 8 primarys?

If you are already fed up with pulling the plenum then I'd say replacing all 16 is the way to go despite the added cost. If however you want to save money or don't mind another possible plenum pull then only replace the one/s you find that are faulty. I say this from experience since I had one leaking injector a couple of years ago and only replaced it. I have not had any others fail, so I am happy with my decision. If however another one went out within a few months then I would feel the opposite.:wink:

As to the cleaning, many (not all) have had problems not to long after spending the money and eventually had to replace them anyway.

So try to keep your chin up and hopefully you will get everything squared away soon.

:cheers:

[GregCrowe]

If you are already fed up with pulling the plenum then I'd say replacing all 16 is the way to go despite the added cost. If however you want to save money or don't mind another possible plenum pull then only replace the one/s you find that are faulty. I say this from experience since I had one leaking injector a couple of years ago and only replaced it. I have not had any others fail, so I am happy with my decision. If however another one went out within a few months then I would feel the opposite.:wink:

As to the cleaning, many (not all) have had problems not to long after spending the money and eventually had to replace them anyway.

So try to keep your chin up and hopefully you will get everything squared away soon.

:cheers:

Well, I do know my problem is on the primary side. Is there a way to isolate it to one specific injector? Being a pre-OBD2 car, can a Tech 2 scantool find the problem on a specific cylinder?

[Tom]

I didn't see any mention of you measuring the injector resistances. It is very easy to do and would quickly tell you if you have injector coils going bad, you don't have to pull the plenum to check them. Here is the link to an article on Marc Haibeck's website about measuring the injector resistance: http://www.zr1specialist.com/HAT%20Web/articles/FI%20Resistance.htm

The diagram on his site is for a '91 though it would be much easier to read in the shop manual if you have one.

[GregCrowe]

Thank you Tom, that looks exactly like what I need to test, specifically where they mention "Solenoid coils are more likely to exhibit shorts when they are hot".

Let me see if I understand what they are saying to do to check primary injectors. Let me know if this is right:

1. Run car long enough to get hot and heat soaked
2. Remove power to ECM
3. Pull Injector 1 fuse from fuse panel on passenger end of dash
4. Test resistance between the right side(closet to nose of the car) of the fuse plug-in ........... and the 8 injector connections on the ECM connector A(A8,A3,A2,A7,A1,A12,A13,A18)

Looks like I'll need to extend the wires on my volt-meter to reach that far.

[1990 quasar blue]

I hear what you're saying. However, I do have a Lingenfelter 383 Corvette and an LS-1 WS6 Trans Am that will both run circles around the ZR-1 so it's not like I'm blown away by it when it is running right.

As to the injectors, is there a reasone to change all 16 or should I just change the 8 primarys?

http://www.zr1specialist.com/HAT%20Web/services/injector%20flow%20testing.htm If you want them tested individually.

If you want to change just 1,2, or 8 go ahead but, you'll be changing the rest sooner or later. I would change them all. Either RC's for 1100.00 or Accells for 500.00. As far as the 383 and the WS6 you're comparing two heavily modded cars to one that's stock and 15 years old. Make that 91 a 415 then reassess.

[GregCrowe]

http://www.zr1specialist.com/HAT%20Web/services/injector%20flow%20testing.htm If you want them tested individually.

If you want to change just 1,2, or 8 go ahead but, you'll be changing the rest sooner or later. I would change them all. Either RC's for 1100.00 or Accells for 500.00. As far as the 383 and the WS6 you're comparing two heavily modded cars to one that's stock and 15 years old. Make that 91 a 415 then reassess.

Please excuse my ignorance but what does "RC" stand for? How about using the 93-95 Multec's referred to on the linked page? Also, I see the Accel part number listed in another thread as 050121(050821 for an 8-pack) and are the secondary injectors the same as the primaries?

[Jeffvette]

RC is Russ Collins

www.rceng.com

[Tom]

The steps you listed will check the primary injector coils only. Take a look at the schematic and you will see why these steps only check the primaries and you will have to make additional measurements to check the secondary injector coils. There is a good chance secondary coils are going bad if the primary coils are failing and you might as well check and take care of everything at the same time.

[GregCrowe]

Thanks Tom, are the secondary injectors the same units as the primaries? IE......... do I just buy two sets of the Accels?

[Tom]

I don't know for sure for your '91, but there are other threads about injectors if you do a search, several of the people who have replied to this thread have replaced their injectors. My '90 with a little over 36,000 miles still has the original injectors, but as far as I can tell I have never used gasoline that had alcohol in it. That will probably change now since California is removing the MTBE and I believe is going to alcohol in the gasoline.

[GregCrowe]

Well, I do know for a fact that I've never used gasoline with alcohol in it. I'll try to do the injector resistance test this weekend.

[1990 quasar blue]

Well, I do know for a fact that I've never used gasoline with alcohol in it. I'll try to do the injector resistance test this weekend.

http://cgi.ebay.com/ebaymotors/Accel-150121-8-21-lb-Fuel-Injectors-ZR1-ZR-1_W0QQitemZ300036567346QQihZ020QQcategoryZ33554QQr dZ1QQcmdZViewItem
You need two sets plus the thicker rubber Orings from Marc Haibeck. I think there twenty bucks. I don't know about the later style injectors. How about ethanol? All the gas here has 10%.

[GregCrowe]

OK cool, now all I need to know is if these Accels can be used on both the primary and secondary side. I do know according to GM parts, the primary and secondary injector part numbers are different.

[jonszr1]

I believe you order 16 same part no of the accels just get the o-ring setup from mark

[1990 quasar blue]

OK cool, now all I need to know is if these Accels can be used on both the primary and secondary side.
Yes.

Lots of info.

http://forums.corvetteforum.com/search.php?searchid=3367392

http://forums.corvetteforum.com/showthread.php?t=1448589&highlight=injectors

[george henry]

My 2 cents: My '90 had a similar problem, cutting out (missing) under load when the engine was hot (all was fine with cold engine). Did all the usual and simple stuff first. The guy's at the corvette shop suspected a coil breaking down when hot. My fuel pressure was 42psi on either pump or both pumps together. Should be 52-55 psi. Is yours still 32psi? not good. Under load the engine would be starving for fuel. Anyway, since the plenum was coming off, I replaced the fuel pressure regulator (pressure is now 52psi) and all four coils. Problem gone, I can now do 180mph again. Regulator was $125 at GMPartsdirect.com.

Good luck

[GregCrowe]

Well, finally after 2 years I have now ordered the Accel fuel injectors and a new fuel pressure regulator. This morning I have a new problem. I am now informed that the 90-92 Corvette ZR1 fuel pressure regulator is a discontinued item. I'm still reading 32 psi with a new fuel filter. Any suggestions on where to get a FPR ? An adjustable one would be ideal.

[Pete]

Well, finally after 2 years I have now ordered the Accel fuel injectors and a new fuel pressure regulator. This morning I have a new problem. I am now informed that the 90-92 Corvette ZR1 fuel pressure regulator is a discontinued item. I'm still reading 32 psi with a new fuel filter. Any suggestions on where to get a FPR ? An adjustable one would be ideal.

Call Lingenfelter Perfomance they have the adjustable.
Price use to be $350.

Pete

[GregCrowe]

Call Lingenfelter Perfomance they have the adjustable.
Price use to be $350.

Pete

Ouch $350. Any other options ?

[Jeffvette]

Ouch $350. Any other options ?

Your dealer is lazy.

17112220


Ray Denison Chevrolet
1-800-527-5452

[Pete]

Ok,more affordable
AutoZone.com
G/P Sorensen Part # 800-311 $109

Pete

[GregCrowe]

Ok,more affordable
AutoZone.com
G/P Sorensen Part # 800-311 $109

Pete

Man you had me excited with that post. However, talked to my Auto Zone guy who had to call GP Sorensen and found out the part is discontinued. Back to square one.

[Pete]

In that case what i would do if the car is not a collector i would modify my feul rails and buy an Aeromotive adjustable regulator from Jeg's for $150 and never have to worry about the regulator again.
I would think modifying the rails and regulator should be a total cost of $200-$250.
I know it costs about the same or a bit more over a stock replacement but here you will have an adjustable and available regulator.

Just my thought.
Pete

[GregCrowe]

Good news, Borg Warner is now making a ZR1 specific fuel pressure regulator. The Borg Warner part number is 22848. It's about $200 but I was able to pull some strings and get it ordered for $140.

[GregCrowe]

I am happy to report that after almost 2 1/2 years, I have now fixed the cutting out problem. Today me and a buddy installed the new Accel injectors and new fuel pressure regulator. It was a 4 hour job. About one hour of that though was cleaning out all the rusty crap from the fuel rails where the injectors plugged in.

After finally doing the injector swap, I have 2 very important pieces of advice for anyone doing an injector swap:

1. PARTIALLY DRAIN THE COOLANT FIRST !!!!!!!!

I didn't drain any coolant and kept fighting coolant coming up thru injector housing and into the front cylinder intake holes. I had to constantly paper towel out the coolant in the front cylinder secondaries. Even after trying to keep the coolant out of the intake holes as best we could, when we first tried to start the motor, it would not turn over. We immediately knew what was happening. We didn't want to risk hydrolocking the motor so we removed the front 2 spark plugs on each side and kept cranking the motor until it blew all the coolant out of the cylinders. It took a little while but we got the coolant all out, put the plugs back in and everything was fine.

#2. After bolting down the fuel rails with the new injectors installed, before installing the plenum, make sure you cycle the key several time to build up fuel pressure and make sure you don't have any leaks. 16 injectors and 32 o-rings can easily add up to 1 little problem. Sure enough, one of the 16 injectors had a small scuff in the upper o-ring and it leaked. Good thing we checked first. After replacing the o-ring all was good.

[GregCrowe]

Well crap, spoke too soon. The cutting out is back. This car is seriously possessed.

See if this makes any sense whatsoever. When you start the car up first thing in the morning, it runs fine. If you let it warm up completely and go drive it around, it runs fine. Consistantly the 2nd time you start the car up each day the cutting out begins. Same thing happened after the injector change. I started the car up, let it fully warm up and drove it around. It ran fine, even doing what really makes it cut out which is to put it in a high gear at low speed. After letting it sit for an hour, I went back out to drive the car and it immediately started cutting out.

Tom, a couple pages ago and probably well over a year ago, you offered to let me borrow your spare PCM for diagnostic purposes. I'd love to take you up on that offer now. At this point about all that's left is the PCM, ignition module and coils.

[tccrab]

The ECM's show up on eBay fairly often.
There's one for sale right now but I'm *very* suspicious.
It's *way* too cheap and I'm pretty sure that the LT1 version is not the same as our LT5 version.

TomC

[GregCrowe]

Do LT5's have camshaft and/or crankshaft position sensors?

Also, where is the ignition module located?

[GregCrowe]

The ECM's show up on eBay fairly often.
There's one for sale right now but I'm *very* suspicious.
It's *way* too cheap and I'm pretty sure that the LT1 version is not the same as our LT5 version.

TomC

How funny, just saw it. The auction says it fits an LT1, LT5, 3.1L Regal, Grand Prix, Lumina and Cutless........... LOL ! Could that actually be accurate ?

[Jeffvette]

Do LT5's have camshaft and/or crankshaft position sensors?

Also, where is the ignition module located?

Yes, camshaft is located on the driver side head in between ports 3 & 5.

Crankshaft is located on passenger side of block.

Ignition module is underneath the plenum.

Neither 3 of these components go bad on a common basis.

[GregCrowe]

Yes, camshaft is located on the driver side head in between ports 3 & 5.

Crankshaft is located on passenger side of block.

Ignition module is underneath the plenum.

Neither 3 of these components go bad on a common basis.

Thanks Jeff. If you've kept up with this thread, I'd sure appreciate some advice on what to try now. So far I have:

1. New Plugs and Wires
2. New Fuel Filter
3. Tested both fuel pumps...... tested OK
4. O2 sensor readings look ok
5. New Accel injectors and Fuel Pressure Regulator

ECM ? Coils ?

[gbrtng]

How funny, just saw it. The auction says it fits an LT1, LT5, 3.1L Regal, Grand Prix, Lumina and Cutless........... LOL ! Could that actually be accurate ?

The L98 ECM crosses to about 10 other GM applications. The LT5 ECM is specific to the ZR-1. Check with your local parts store or junk yard.

[Jeffvette]

ECM ? Coils ?


Coils.


When hot, pull each plug wire and listen for the sound of the spark arcing.

[GregCrowe]

Coils.


When hot, pull each plug wire and listen for the sound of the spark arcing.

I don't think that will help. When hot, the car idles perfectly and runs perfectly unless under fairly heavy load.

[Pete]

I would try changing the spark plugs again.
It's cheap and easy.
Just try the cheap AC-Delco 41-602 cost about $15
You never know if some parts guy droped them.
I seen a guy throwing plugs on the counter from about 10ft away to see if he could land them on the counter like he was playing basketball :jawdrop:
Otherwise check Coils.
Pete

[GregCrowe]

I would try changing the spark plugs again.
It's cheap and easy.
Just try the cheap AC-Delco 41-602 cost about $15
You never know if some parts guy droped them.
I seen a guy throwing plugs on the counter from about 10ft away to see if he could land them on the counter like he was playing basketball :jawdrop:
Otherwise check Coils.
Pete

The car runs the exact same as it did before and after the spark plug/wire change. I can't see any reason to change the plugs again, especially considering how the problem has it's weird intermintantcy, appearing after the car sits while being hot.

[LT5-Lee]

Haven't had a problem with this car in years until today. The car had been sitting for awhile so I decided it was time to break it out of the garage and take it for a spin. We made a 10 mile trip and the car was perfect, even while spanking a Mustang on the highway. After sitting for 30 minutes, we hopped back in and the car immediately had a problem.

At idle, it's perfect, at highway cruise, it's perfect. At any kind of load situation, it has a stuttering, cutting out problem. The heavier the load, the worse the problem is. If you put the car in 5th gear and bog it down at like 20 mph, the car literally shakes.

I'm almost positive it's not a mechanical engine problem. It seems electrical or sensor/vacuum related. The only problem I have ever had with this car is a little 5 cent clip falling off the arm of one of the secondary intake flap solonoids. When that happened, it was just down on power.

Any ideas? I'm dreading having to take this car into the Chevy dealership with a blank check.

Edit: Forgot to add, it makes no difference whether the secondary systems are engaged with the key. Either way, it has the stuttering problem.


Howdy, I was just curious if anything else has been learned since the last postings?

I am very curious as I think I have basically a '91 with "carbon copy" symptoms of your problems also!:dontknow:

I just started checking everything before a plenum pull, but I already have RC injectors and a fuel filter replaced. I guess I was hoping it was bad gas, but I know better since it ran good without any fill up in between.

Anyway, just hoping it is not a ECM.:(

Lee

[GregCrowe]

Howdy, I was just curious if anything else has been learned since the last postings?

I am very curious as I think I have basically a '91 with "carbon copy" symptoms of your problems also!:dontknow:

I just started checking everything before a plenum pull, but I already have RC injectors and a fuel filter replaced. I guess I was hoping it was bad gas, but I know better since it ran good without any fill up in between.

Anyway, just hoping it is not a ECM.:(

Lee

Lee, I'm so disgusted with this car. I can't seem to be able to fix it. It's been almost 3 years since my first post and the car has just sat in the garage. I've only driven it maybe 10 miles. At this point I'm totally worn out on it and tired of throwing money at it. The only thing I can figure now that might be a possibility is:

1. ECM
2. Ignition Control Module
3. Coils

I'm sick of pulling the plenum. I'd love to try another ECM and see if that fixes it. Someone out here once offered to let me try their spare but never replied back. My ZR1 just sits in the garage. I don't drive it, can't sell it like this........ totally disgusted with it. It's a giant paperweight taking up space in my garage.

[Zr1 Destroyer]

Try the coils first since they are cheap and easy to replace!

[jonszr1]

you arent that far from corey henderson ,new braunfels texas 210 867 6286 .why not tow it to him and have him fix it for you he is one of the best on these cars. couldnt hurt .as its got under your skin .

[lbszr]

Mine had similar issures with two coils bad and the restistance was way out on two of them and the missing was intermittent. Autozones coils lasted one year, slight intermittent miss came back, resistance checked good on all four but changing them to Standard coils the miss has been gone for a few years so far. And I found brand new not all coils checked the same. Parts stores probably didn't like see me showing up with a multimeter. Some were twice the resistance.

[Jeffvette]

Lee, I'm so disgusted with this car. I can't seem to be able to fix it. It's been almost 3 years since my first post and the car has just sat in the garage. I've only driven it maybe 10 miles. At this point I'm totally worn out on it and tired of throwing money at it. The only thing I can figure now that might be a possibility is:

1. ECM
2. Ignition Control Module
3. Coils

I'm sick of pulling the plenum. I'd love to try another ECM and see if that fixes it. Someone out here once offered to let me try their spare but never replied back. My ZR1 just sits in the garage. I don't drive it, can't sell it like this........ totally disgusted with it. It's a giant paperweight taking up space in my garage.


Greg, send me your address and I'll send you a ECM to test. The DIS modules rarely go bad, and I'm still suggesting coils.

[XfireZ51]

Lee, I'm so disgusted with this car. I can't seem to be able to fix it. It's been almost 3 years since my first post and the car has just sat in the garage. I've only driven it maybe 10 miles. At this point I'm totally worn out on it and tired of throwing money at it. The only thing I can figure now that might be a possibility is:

1. ECM
2. Ignition Control Module
3. Coils

I'm sick of pulling the plenum. I'd love to try another ECM and see if that fixes it. Someone out here once offered to let me try their spare but never replied back. My ZR1 just sits in the garage. I don't drive it, can't sell it like this........ totally disgusted with it. It's a giant paperweight taking up space in my garage.

Greg,

Boy this has been going on too long. I sympathize with your frustration. I strongly doubt its either the ECM or the module.
I have a set of stock coils that worked fine before I replaced them with
MSDs. Let me know if you'd like to try them out. Its a shame to see a perfectly good ZR go to waste.

[XfireZ51]

Well, finally after 2 years I have now ordered the Accel fuel injectors and a new fuel pressure regulator. This morning I have a new problem. I am now informed that the 90-92 Corvette ZR1 fuel pressure regulator is a discontinued item. I'm still reading 32 psi with a new fuel filter. Any suggestions on where to get a FPR ? An adjustable one would be ideal.

Did you ever pull the fuel pumps?
I didn't catch how many miles were on the car but the 30psi at idle isn't right. Has that been rectified? If not and you've changed the fuel filter, I would look at the sock filter on both pumps. They may be plugged to the point that they'll look like they are being sucked in by pumps. In that case I would replace the pumps since they probably been overheating trying to get fuel out. I had problem with my fuel pump filter causing the secondaries to shut down due to lean O2.

[ZR1Vette]

I looked thru the FSM and found these...just in case you need more options to consider>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1troubleshootingsagstumble.jpg

http://i17.photobucket.com/albums/b79/MRBLU/ZR1troubleshootingsluggish.jpg

[XfireZ51]

Fuel system is the first thing on both these lists. The stumbling that happens when the accelerator is moved can be due to the lack of or insufficient pump shot. Without sufficient fuel pressure there isn't enough fuel and the mixture goes lean causing the momentary stumble and lack of power.

[GregCrowe]

Mine had similar issures with two coils bad and the restistance was way out on two of them and the missing was intermittent. Autozones coils lasted one year, slight intermittent miss came back, resistance checked good on all four but changing them to Standard coils the miss has been gone for a few years so far. And I found brand new not all coils checked the same. Parts stores probably didn't like see me showing up with a multimeter. Some were twice the resistance.

Did your car have to heat synch before you started having miss/coil problems? That's the crazy part about my car. Also, what are you calling "Standard" coils. Where do you find good ones for a decent price?

[GregCrowe]

Did you ever pull the fuel pumps?
I didn't catch how many miles were on the car but the 30psi at idle isn't right. Has that been rectified? If not and you've changed the fuel filter, I would look at the sock filter on both pumps. They may be plugged to the point that they'll look like they are being sucked in by pumps. In that case I would replace the pumps since they probably been overheating trying to get fuel out. I had problem with my fuel pump filter causing the secondaries to shut down due to lean O2.

Fuel pumps test out OK. I replaced the FP Regulator during the injector swap. My FP is normal now.

[GregCrowe]

Fuel system is the first thing on both these lists. The stumbling that happens when the accelerator is moved can be due to the lack of or insufficient pump shot. Without sufficient fuel pressure there isn't enough fuel and the mixture goes lean causing the momentary stumble and lack of power.

The problem is not consistant with a fuel problem. It feels very "electrical" like the spark just disappears for a split second. The hotter the car, the more it has heat synched, the worse the problem.

[GregCrowe]

Looking at these coils on both Auto Zone and OReillys websites and it looks like the ZR-1 coils are the same generic thing as the 3 coils on a 3.8L V6 which I know are always problems. Is that right? The same coil? I can't even tell you how many of those things I've replaced on 3.8L's.

[LT5-Lee]

Lee, I'm so disgusted with this car. I can't seem to be able to fix it. It's been almost 3 years since my first post and the car has just sat in the garage. I've only driven it maybe 10 miles. At this point I'm totally worn out on it and tired of throwing money at it. The only thing I can figure now that might be a possibility is:

1. ECM
2. Ignition Control Module
3. Coils

I'm sick of pulling the plenum. I'd love to try another ECM and see if that fixes it. Someone out here once offered to let me try their spare but never replied back. My ZR1 just sits in the garage. I don't drive it, can't sell it like this........ totally disgusted with it. It's a giant paperweight taking up space in my garage.


There you go, JeffVette to the rescue.=D>

[Tyler Townsley]

The problem is not consistant with a fuel problem. It feels very "electrical" like the spark just disappears for a split second. The hotter the car, the more it has heat synched, the worse the problem.

Beg borrow or steel a fuel pressure guage. Hook it up and pop the hood enough to feed the hose out and tape the guage to the windshield. Take the car for a run watch the pressure when the symtoms happen, fuel starvation mimics an electrical problem on a efi car since it will show up as a lean condition at a cyl much like a spark problem at same cyl. Its a cheap check.

Another check is the plugs, do they show a lean condition? If they show soot then one could suspect spark, if lean then fuel.

A quick check on spark is to pull all plugs then take a good plug and put it in each wire one at a time and lay it on the plenum. Crank motor and watch the spark all cyl should show same spark, I actually just pull the plug wire and put a plug in and lay it on the plenum and crank the car, in this way I can see if a cyl is bad for other reasons.

If you want to check individual injectors you can pull the plenum, lift the injector rails up, make a pigtail to connect to the injector and pulse it with 12 volts and watch the spray pattern. You will have to cycle the key to pressurize the rail but its cheap way to check them, also make resistance checks at the same time.

Tyler

[GregCrowe]

Beg borrow or steel a fuel pressure guage. Hook it up and pop the hood enough to feed the hose out and tape the guage to the windshield. Take the car for a run watch the pressure when the symtoms happen, fuel starvation mimics an electrical problem on a efi car since it will show up as a lean condition at a cyl much like a spark problem at same cyl. Its a cheap check.

Already done this, fuel pressure never drops. With the new fuel pressure regulator, pressure it exactly where it should be. Once again, I've already tested the pumps, they test fine. This is not a fuel problem. The more the car heat synchs the worse the condition gets and it has to be put under a load. Normal driving you will hardly notice it. The more the load, the more it cuts out.


Another check is the plugs, do they show a lean condition? If they show soot then one could suspect spark, if lean then fuel.

Plugs are fine, new and look great.



A quick check on spark is to pull all plugs then take a good plug and put it in each wire one at a time and lay it on the plenum. Crank motor and watch the spark all cyl should show same spark, I actually just pull the plug wire and put a plug in and lay it on the plenum and crank the car, in this way I can see if a cyl is bad for other reasons.

Plugs are new and fine, wires are new and fine. These tests will show nothing since the car has to be heat synched and put under a load. The problem is electrical.


If you want to check individual injectors you can pull the plenum, lift the injector rails up, make a pigtail to connect to the injector and pulse it with 12 volts and watch the spray pattern. You will have to cycle the key to pressurize the rail but its cheap way to check them, also make resistance checks at the same time.

Tyler

Just replaced the injectors and fuel pressure regulator. Injectors are fine. It pretty much has to be coils, ignition control module, ECM or some crazy grounding problem at this point.

[Pete]

What plugs are in your Z?
Where did you gap them?
Just because something is new don't mean sh!t.


Can somebody tell me where the RPM's would be at in 5th at 20MPH since he's problem happen's at this point.

Pete

[Tyler Townsley]

They make a DIS module checker, I have one but you might find one local as it will check a LOT of cars with these modules. You also need a scope to watch the spark as you change rpm. The advantage of the checker is you do not have to pull the plenum to check them. I had a problem with one that did not show up until 400 rpm where it began to fall apart. The dis modules are expensive when you can find them.

Re read the thread. To answer a question asked early on and never answered. The O2 sensors information is not used in WOT or power enrichment situations, the ecm jumps to calibration tables that are in the chip. The sensors used in the LT 5 are narrow band and the readings are only accurate in a VERY narrow range around stoic afr 14.7. Any voltages beyond this point high or low are meaningless. The dis module is subject to heat hense the type of grease they used when mounting it to the bottom of the plenum, it was there to promote cooling as the airflow through the plenum cools the plenum base as you drive. Not using this grease when removing/replacing the module begs for future failures. If you want to borrow my checker let me know I have lent it out in the past.

Tyler

[GregCrowe]

What plugs are in your Z?
Where did you gap them?
Just because something is new don't mean sh!t.



Pete

Well, in this case it is sh!t. The car did the exact same thing before the plug change and after it. Same with plug wires, same with the fuel filter, same with injectors, same with fuel pressure regulator. Plugs are gapped at factory specs........ don't remember what that was, been over 2 years.

[GregCrowe]

They make a DIS module checker, I have one but you might find one local as it will check a LOT of cars with these modules. You also need a scope to watch the spark as you change rpm. The advantage of the checker is you do not have to pull the plenum to check them. I had a problem with one that did not show up until 400 rpm where it began to fall apart. The dis modules are expensive when you can find them.

Re read the thread. To answer a question asked early on and never answered. The O2 sensors information is not used in WOT or power enrichment situations, the ecm jumps to calibration tables that are in the chip. The sensors used in the LT 5 are narrow band and the readings are only accurate in a VERY narrow range around stoic afr 14.7. Any voltages beyond this point high or low are meaningless. The dis module is subject to heat hense the type of grease they used when mounting it to the bottom of the plenum, it was there to promote cooling as the airflow through the plenum cools the plenum base as you drive. Not using this grease when removing/replacing the module begs for future failures. If you want to borrow my checker let me know I have lent it out in the past.

Tyler

Please excuse my ignorance but what is a DIS module?

[Jeffvette]

Please excuse my ignorance but what is a DIS module?


What you are calling the Ignition Control Module.

[lbszr]

Looking at these coils on both Auto Zone and OReillys websites and it looks like the ZR-1 coils are the same generic thing as the 3 coils on a 3.8L V6 which I know are always problems. Is that right? The same coil? I can't even tell you how many of those things I've replaced on 3.8L's.


I wouldn't buy auto zone's coils, tried that. Think they are the same.

[Zr1 Destroyer]

If you want to borrow my checker let me know I have lent it out in the past.

TylerI might take you up on that dis checker.

[XfireZ51]

They make a DIS module checker, I have one but you might find one local as it will check a LOT of cars with these modules. You also need a scope to watch the spark as you change rpm. The advantage of the checker is you do not have to pull the plenum to check them. I had a problem with one that did not show up until 400 rpm where it began to fall apart. The dis modules are expensive when you can find them.

Re read the thread. To answer a question asked early on and never answered. The O2 sensors information is not used in WOT or power enrichment situations, the ecm jumps to calibration tables that are in the chip. The sensors used in the LT 5 are narrow band and the readings are only accurate in a VERY narrow range around stoic afr 14.7. Any voltages beyond this point high or low are meaningless. The dis module is subject to heat hense the type of grease they used when mounting it to the bottom of the plenum, it was there to promote cooling as the airflow through the plenum cools the plenum base as you drive. Not using this grease when removing/replacing the module begs for future failures. If you want to borrow my checker let me know I have lent it out in the past.

Tyler


Tyler,

Any chance you have a pic of this DIS checker?

[Pete]

Well, in this case it is sh!t. The car did the exact same thing before the plug change and after it. Same with plug wires, same with the fuel filter, same with injectors, same with fuel pressure regulator. Plugs are gapped at factory specs........ don't remember what that was, been over 2 years.

Plugs i would gap at .035 no matter what year Z you have.

The other question still remains.
"What plugs do you have?"

I asked you this 2 years ago and never got an answer and am still asking.

I hope not the Bosch Platinum,if so change them to AC Delco 41-602 gaped at .035

Plugs are cheap and easy to change.
Coils are more $$$ and harder to change.

Also can somebody take there Z with stock rear gears for a ride and tell me what RPM your at in 5th gear at 20 MPH, mine is all apart.

Help us help you.
Pete

[Tyler Townsley]

OTC 3575 or PRI Ignition System Simulator

Tyler

[GregCrowe]

Plugs i would gap at .035 no matter what year Z you have.

The other question still remains.
"What plugs do you have?"

I asked you this 2 years ago and never got an answer and am still asking.



A/C Delcos before, A/C Delcos after. No change.

[gbrtng]

Greg:

Please describe "cutting out". Does the engine completely die and then recover when you lift from the accelerator pedal, bog down under full throttle and then recover, or miss heavily or slightly and then recover? I think you said earlier that power key selection does not matter. Please confirm - we're here to help, honest.

[John Boothby]

Plugs i would gap at .035 no matter what year Z you have.

The other question still remains.
"What plugs do you have?"

I asked you this 2 years ago and never got an answer and am still asking.

I hope not the Bosch Platinum,if so change them to AC Delco 41-602 gaped at .035

Plugs are cheap and easy to change.
Coils are more $$$ and harder to change.

Also can somebody take there Z with stock rear gears for a ride and tell me what RPM your at in 5th gear at 20 MPH, mine is all apart.

Help us help you.
Pete

This morning, my '90 ran 650-700 RPM in 5th at 20mph.

[GregCrowe]

Greg:

Please describe "cutting out". Does the engine completely die and then recover when you lift from the accelerator pedal, bog down under full throttle and then recover, or miss heavily or slightly and then recover? I think you said earlier that power key selection does not matter. Please confirm - we're here to help, honest.

OK, in complete detail:

When the car is cold or even just warm and being driven for the 1st 15 minutes, no issues whatsoever, even with full throttle. After the car has been driven and has sat, heat synching the engine, the miss begins. Normal driving with light throttle, no issue. When a load is applied, the miss begins. The miss is very "electrical" feeling. It does not come and go under heavy fuel delivery situations. It's just a very quick electrical miss and shudder. The car never dies nor does it even come close to dying. Again, it's only under medium to heavy load. If you want to make it miss the absolute worst, let it heat synch and then bog it down in a high gear at low speed and floor the gas. Then the car will shudder and jerk. If you try to accelerate through the gears at full throttle, the car just plain misses like it has 2-3 bad plug wires arching.

[GregCrowe]

I'm starting to think ECM. Think about this guys. How many times in your lifetime have you messed with a car and then had something start acting up. You always think that the last thing you did to the car could not have possibly caused the problem but sure enough, after driving yourself crazy, you discover that whatever the hell you did caused the problem.

Back in the very beginning of this thread, I said that this problem happened exactly the time after changing the PROM from a Doug Rippie to a newer redesigned GM. Replacing the PROM back to the Rippie made no difference, same cutting out.

The very first thing I asked out here was could screwing around with the PROMs have caused a problem with the ECM. Everyone said no way. I am now guessing that somehow something inside the ECM must have gotten screwed up. I think I will take up the offer from JeffVette to try the spare ECM. At least that way I won't be out any more significant money and I won't have to pull the plenum again.

[LT5-Lee]

I'm starting to think ECM. Think about this guys. How many times in your lifetime have you messed with a car and then had something start acting up. You always think that the last thing you did to the car could not have possibly caused the problem but sure enough, after driving yourself crazy, you discover that whatever the hell you did caused the problem.

Back in the very beginning of this thread, I said that this problem happened exactly the time after changing the PROM from a Doug Rippie to a newer redesigned GM. Replacing the PROM back to the Rippie made no difference, same cutting out.

The very first thing I asked out here was could screwing around with the PROMs have caused a problem with the ECM. Everyone said no way. I am now guessing that somehow something inside the ECM must have gotten screwed up. I think I will take up the offer from JeffVette to try the spare ECM. At least that way I won't be out any more significant money and I won't have to pull the plenum again.


These were the classic symptoms in the early days of the first "brain" failures, suffered mainly by Fords. The heat would cause the epoxy "brain buckets" would ooze out like a molasses leak and it was relatively easier to diagnose.

I was doing some time surfing the net for other mass ECM failures and it seems the Mitsubishi guys were hit pretty bad for the same issue. They have traced it down to one common and almost predictable failure, especially in the early '90's involving guess what?... A bad batch of "leaking capacitors"... sound familiar?

Maybe the question should be, why haven't all early ECM's failed like our Bloose amplifiers? :mad:

Has anybody noticed any NOS units failure rate to be higher than later rebuilt units or have any data of when GM's manufacturing runs of ECM's have held up better?

Lee

[jonszr1]

i could be nuts but it sure sounds like coils ,when cold they are fine but once they start to get hot they break down. i have had this happen in ca couple of my carbed cars. also if you werent carefully putting the prom back in you might have bent atang or loosened the solder connection on a tang . just a couple of thoughts i had . stick with the guys they will help you till you find it . they hate seeing a zr1er not being able to drive their ride ;)

[GregCrowe]

i could be nuts but it sure sounds like coils ,when cold they are fine but once they start to get hot they break down. i have had this happen in ca couple of my carbed cars. also if you werent carefully putting the prom back in you might have bent atang or loosened the solder connection on a tang . just a couple of thoughts i had . stick with the guys they will help you till you find it . they hate seeing a zr1er not being able to drive their ride ;)

I think we're on the right track. I'll try the spare ECM first since it's a cheap test and if that doesn't fix it I'll pull the plenum once again and replace the coils.

If this thing ever gets fixed it really should run great, everything is freaking new.

Also........ yes, very very familiar with the Mitsubishi capacitor leakage. All Eclipses and 3000GT's have this failure from like 93-99.

[Zr1 Destroyer]

coils.....

[LT5-Lee]

I think we're on the right track. I'll try the spare ECM first since it's a cheap test and if that doesn't fix it I'll pull the plenum once again and replace the coils.

If this thing ever gets fixed it really should run great, everything is freaking new.

Also........ yes, very very familiar with the Mitsubishi capacitor leakage. All Eclipses and 3000GT's have this failure from like 93-99.


Gregg, if it's not, I want your car to sell to my brother-in-law. ;)

I am almost in OK. pretty regularly (Texoma). How would you feel about some trading?.... :handshak:

Lee

[GregCrowe]

Gregg, if it's not, I want your car to sell to my brother-in-law. ;)

I am almost in OK. pretty regularly (Texoma). How would you feel about some trading?.... :handshak:

Lee

Ahhhh, I'll get it fixed eventually. It may take 10 years but I'll get it fixed.

[GregCrowe]

I'd like to take a moment to throw out a public THANK YOU to JeffVette who is at this moment sending me a ZR1 ECM to try. Thanks Jeff, much appreciated. I'll report back when I give the ECM a shot.

[LT5-Lee]

Ahhhh, I'll get it fixed eventually. It may take 10 years but I'll get it fixed.


I don't blame you. If it is a ECM, I sure would be curious if the problem was a few bad capacitors that puked out their guts?

[Jeffvette]

I'd like to take a moment to throw out a public THANK YOU to JeffVette who is at this moment sending me a ZR1 ECM to try. Thanks Jeff, much appreciated. I'll report back when I give the ECM a shot.


Greg, ECM left today.

[gbrtng]

My experience with a bad ECM: 2 or 3 unrelated error codes would set. As soon as the check engine lit, the engine would barely run or just stop and not restart. I could not isolate the problem to heat soak because it would happen at any outside and underhood
temperature. Replaced several ignition components with no change. Corey hooked up his Tech 1 and left baffled after an hour. I finally decided to change the ECM and yep, that was the problem. This was on Mary's 91 L98 which uses a common junk yard ECM - I was able to score one locally for $55 - which crosses to about 10 other GM vehicles.

[XfireZ51]

My experience with a bad ECM: 2 or 3 unrelated error codes would set. As soon as the check engine lit, the engine would barely run or just stop and not restart. I could not isolate the problem to heat soak because it would happen at any outside and underhood
temperature. Replaced several ignition components with no change. Corey hooked up his Tech 1 and left baffled after an hour. I finally decided to change the ECM and yep, that was the problem. This was on Mary's 91 L98 which uses a common junk yard ECM - I was able to score one locally for $55 - which crosses to about 10 other GM vehicles.

L98's had a well documented issue with ECM. Something about the board material being a bit flimsy and the circuits developing micro-cracks.
I'm in the "innocent till proven guilty" :rolleyes:camp when it comes to an ECM causing the kind of issues being discussed in this thread.

[GregCrowe]

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is ;)

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

[XfireZ51]

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is ;)

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

Given those 2 choices, I'd pick coils altho I'm not convinced it's that either. I wouldn't be doing anything until I had a scan. With all the time that has gone by, there should have been a way to connect a scantool to this motor. :dontknow:

[LT5-Lee]

Jeff tends to think 75-80% chance it's a coil problem, 20-25% chance it's the ECM. Taking bets on what it is ;)

If it's either of the 2, I'll have it fixed in not too long.

Then I get to take the car up to the tag agency and explain to them why it hasn't been tagged in 3 years......... LOL.

ECM, wiring or MEM-CALl. Some corrosion somewhere.

[LT5-Lee]

OK, in complete detail:

When the car is cold or even just warm and being driven for the 1st 15 minutes, no issues whatsoever, even with full throttle. After the car has been driven and has sat, heat synching the engine, the miss begins. Normal driving with light throttle, no issue. When a load is applied, the miss begins. The miss is very "electrical" feeling. It does not come and go under heavy fuel delivery situations. It's just a very quick electrical miss and shudder. The car never dies nor does it even come close to dying. Again, it's only under medium to heavy load. If you want to make it miss the absolute worst, let it heat synch and then bog it down in a high gear at low speed and floor the gas. Then the car will shudder and jerk. If you try to accelerate through the gears at full throttle, the car just plain misses like it has 2-3 bad plug wires arching.

Greg, I think I found my gremlin..=D>

and I can't believe what it turned out to be. I was wiggling everything while the engine was idling and for the hundredth time, I played with all the sensors and then the MAP sensor and the engine died? I swear I checked it out many times, but it seems the rubber accordion seal on the connector must have gotten twisted and was not quite snapped on tight. My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection? :dontknow:

I can not believe it because it was one of the first things I suspected and always made sure it was tight, but I had to squeeze it so hard before I heard the plastic snap, I thought I was going to need some channel locks before I actually heard it snap on!!!

I maybe a little premature as I have only made a few hard runs for testing it out because of traffic, but knock on wood, I hope I got it!

After doing some data logging I probably have some other issues that made it worse, like a lazy LH o2 sensor with low cross counts (or a really slow scan tool "Auto X-ray"),but I am preying the MAP sensor connector was the major problem. My problem wasn't just heat related, but it chugged so bad it felt like it would throw you into the windshield just like you described so I thought I would just pass along my good fortune just in case?

[XfireZ51]

"My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection? :dontknow:"

If you had put the scan tool on and datalogged while driving, I'll bet you would have seen the MAP voltage drop under load. ;)

[GregCrowe]

Greg, I think I found my gremlin..=D>

and I can't believe what it turned out to be. I was wiggling everything while the engine was idling and for the hundredth time, I played with all the sensors and then the MAP sensor and the engine died? I swear I checked it out many times, but it seems the rubber accordion seal on the connector must have gotten twisted and was not quite snapped on tight. My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection? :dontknow:

I can not believe it because it was one of the first things I suspected and always made sure it was tight, but I had to squeeze it so hard before I heard the plastic snap, I thought I was going to need some channel locks before I actually heard it snap on!!!

I maybe a little premature as I have only made a few hard runs for testing it out because of traffic, but knock on wood, I hope I got it!

After doing some data logging I probably have some other issues that made it worse, like a lazy LH o2 sensor with low cross counts (or a really slow scan tool "Auto X-ray"),but I am preying the MAP sensor connector was the major problem. My problem wasn't just heat related, but it chugged so bad it felt like it would throw you into the windshield just like you described so I thought I would just pass along my good fortune just in case?

Congrats, hope that's all it is. That can't be my problem. I've had the plenum off and MAP disconnected multiple times during this ordeal. Just got Jeff's spare ECM in (weird part number: 16148441). Going to give it a try Saturday.

[LT5-Lee]

"My scan tool showed the correct voltage readings, but I guess when the engine torqued just right it lost connection? :dontknow:"

If you had put the scan tool on and datalogged while driving, I'll bet you would have seen the MAP voltage drop under load. ;)


I did, and it followed the throttle angle/voltage and engine RPM closely under load so I thought it looked fine, It idled at 750 RPM with 1.37v and at 0 rpm it read 4.84v EOKO. It did loose voltage about the time the secondaries should kick in so I figured that's about right (3300 rpm) with the drop in vacuum. Maybe I still have a grounding problem and just being fooled?

I still want to check all major grounds for grins and need some more practice and experience in diagnosing the sensors. Right now it sure looks like something is wrong with my o2 sensor.

Greg, all I am trying to say is did you hear it snap on, or did you just figure it has to be since it survived a death grip?

[XfireZ51]

Lee,

MAP sensor going to 0 v when opening
the throttle is the opposite of what should have been happening. That's the clue a scan can provide. It didn't last long enough to throw a code but it affected your throttle response

[GregCrowe]

Gave Jeff's ECM a try, and as the norm with this car.......... not fixed. At this point it pretty much has to be coils. I see both Summit and Jeggs have their own high performance, low resistance coils for $31-33 each. I think I'll give the Summit coils a shot, not too expensive and they're red which will match the car and plug wires. If that doesn't fix it, I'm totally stumped.

[Jagdpanzer]

Wow, 33 months, 132 posts, and 7,274 looks later and the problem is still not solved!!
This has to be some kind of a record.
Brother please don't give up now, you've got the entire nation of the ZR-1 brotherhood pulling for you.
While you're at it replacing the coils you might as well replace the plug wires if you have not done so earlier.
Saw an Accel set listed over on ebay that may be had reasonably:
http://cgi.ebay.com/ebaymotors/Accel-Red-8mm-Wires-89-95-Corvette-ZR-1-LT5-DOHC-32_W0QQitemZ250376315110QQcmdZViewItemQQptZMotors_ Car_Truck_Parts_Accessories?hash=item250376315110&_trksid=p4506.c0.m245&_trkparms=65%3A2%7C39%3A1%7C240%3A1318
Good luck and may the force be with you.

[GregCrowe]

Wow, 33 months, 132 posts, and 7,274 looks later and the problem is still not solved!!
This has to be some kind of a record.
Brother please don't give up now, you've got the entire nation of the ZR-1 brotherhood pulling for you.
While you're at it replacing the coils you might as well replace the plug wires if you have not done so earlier.
Saw an Accel set listed over on ebay that may be had reasonably:
http://cgi.ebay.com/ebaymotors/Accel-Red-8mm-Wires-89-95-Corvette-ZR-1-LT5-DOHC-32_W0QQitemZ250376315110QQcmdZViewItemQQptZMotors_ Car_Truck_Parts_Accessories?hash=item250376315110&_trksid=p4506.c0.m245&_trkparms=65%3A2%7C39%3A1%7C240%3A1318
Good luck and may the force be with you.

Done a long time ago, plugs and wires, and fuel filter, and fuel injectors, and fuel pressure regulator and ECM and............ blah blah blah :(

[XfireZ51]

Greg,

Sorry you're not closer to Chicago. :(

[GregCrowe]

Here's the next try:

http://static.summitracing.com/global/images/prod/large/sum-850017_w.jpg

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D850017&N=700+400304+309371+115&autoview=sku

[XfireZ51]

http://www.msdignition.com/product.aspx?id=5059


I installed these last spring on one of the several occasions I found excuse to pull the plenum. So far so good. Let me suggest that before spending the money on those, if you'd like to borrow my set of stock coils and see what happens, let me know. I'm intrigued.

[Jagdpanzer]

Does anyone know if these MSD 8224 coils will work on our ZR-1s?
http://static.summitracing.com/global/images/prod/large/msd-8224.jpg
http://store.summitracing.com/partdetail.asp?part=MSD%2D8224&view=1&N=700+150

[XfireZ51]

Does anyone know if these MSD 8224 coils will work on our ZR-1s?
http://static.summitracing.com/global/images/prod/large/msd-8224.jpg
http://store.summitracing.com/partdetail.asp?part=MSD%2D8224&view=1&N=700+150


See above.

[GregCrowe]

Does anyone know if these MSD 8224 coils will work on our ZR-1s?
http://static.summitracing.com/global/images/prod/large/msd-8224.jpg
http://store.summitracing.com/partdetail.asp?part=MSD%2D8224&view=1&N=700+150



Yes, they will all work. This is what's called a DIS coil for all GM cars using these type coils. As far as supposedly high performance verions, there is:

1. The MSD
2. The Accel
3. The Summit
4. The Jeggs

All 4 look like pretty much the same thing, all with brass terminals. They are probably all 4 made by the same place. The Summit and Jeggs versions are the cheapest.

[scottfab]

Well well well.... that was a novel. I just read all posts from the beginning to the most recent.
I had heard about this thread a couple of years ago from Jeff Flint and very sorry to see it is still active.
Let me toss out my thoughts and story.

I fought an illusive problem on my ZR1 in 1998 after having the car for about 2yrs. I drove it to the midwest and back and it developed this stumble on acceleration. As a result I ended up developing a pattern check jig for the injectors after studying the data from my scan tool.
(Diacom). No good, still stumbled so I bought RC injectors (not a mistake because of the stainless steal construction of the RC) still had the stumble. I bought a spare ECM (not a mistake as it turns out cause to pass the state inspection it is easier to replace the ECM than the chip, and safer) still had the stumble. The fuel pump #2 then failed (unrelated problem) still had stumble. I then developed an emissions problem which after much searching turned out to be the CATS. Returning to the search for the stumble I next replace the coils. Fix! It toot took several years of slowly going at it. The only difference in my case is I would drive it anyway even with the problem. That is what uncovered it since eventually the plugs told the story. I learned a LOT about the car and reading the scan data.
I hope the coils fix it !!!

PS. I am going to toss my bosh/platinums ...... I just checked the plugs as a result of reading the thread (novel) and #3 was fouled. I put in a used AC plug (since I keep spared of many many working parts) and the fouling stopped........hmmmm)

[jonszr1]

when a coil goes bad does it allways effect both cylinders or can it only effect 1 cylinder ???/

[scottfab]

when a coil goes bad does it allways effect both cylinders or can it only effect 1 cylinder ???/

Both if it is the coil. My latest experience was with a single plug (#3) so I knew it was not the coil.

[Jeffvette]

Both if it is the coil. My latest experience was with a single plug (#3) so I knew it was not the coil.

Not always true, sometimes the coil will fail on an individual tower. I've seen it a couple of times.

[GregCrowe]

Well well well.... that was a novel. I just read all posts from the beginning to the most recent.
I had heard about this thread a couple of years ago from Jeff Flint and very sorry to see it is still active.
Let me toss out my thoughts and story.

I fought an illusive problem on my ZR1 in 1998 after having the car for about 2yrs. I drove it to the midwest and back and it developed this stumble on acceleration. As a result I ended up developing a pattern check jig for the injectors after studying the data from my scan tool.
(Diacom). No good, still stumbled so I bought RC injectors (not a mistake because of the stainless steal construction of the RC) still had the stumble. I bought a spare ECM (not a mistake as it turns out cause to pass the state inspection it is easier to replace the ECM than the chip, and safer) still had the stumble. The fuel pump #2 then failed (unrelated problem) still had stumble. I then developed an emissions problem which after much searching turned out to be the CATS. Returning to the search for the stumble I next replace the coils. Fix! It toot took several years of slowly going at it. The only difference in my case is I would drive it anyway even with the problem. That is what uncovered it since eventually the plugs told the story. I learned a LOT about the car and reading the scan data.
I hope the coils fix it !!!

PS. I am going to toss my bosh/platinums ...... I just checked the plugs as a result of reading the thread (novel) and #3 was fouled. I put in a used AC plug (since I keep spared of many many working parts) and the fouling stopped........hmmmm)

Wow, wish you had posted a long, long time ago. If you'll look back in the thread, you will see that absolutely everyone was saying fuel injectors. That delayed me for quite awhile. I'm still waiting on the Summit coils to be delivered. Your story gives me hope. Maybe by next weekend I'll have the car running perfect again.

[Jeffvette]

Wow, wish you had posted a long, long time ago. If you'll look back in the thread, you will see that absolutely everyone was saying fuel injectors. That delayed me for quite awhile. I'm still waiting on the Summit coils to be delivered. Your story gives me hope. Maybe by next weekend I'll have the car running perfect again.


Greg, more than likely your injectors were sketchy anyways. If the coils do solve the problem, your car will run pretty sweet.

I still stand by my suggestion of pulling the plug boot off while the motor is running. A strong coil will have an audible pop to it. A weak coil will not arc at all.

http://www.zr1netregistry.com/forum/showthread.php?t=4667

[GOLDCYLON]

Jeffvette ='s Nice guy and great American :thumbsup:

[GrayZ]

Greg, here's a thought

drive it to, M. Haibecks in chicago and fly home.

another thought, contact Corey Henderson
he will be in Oklahoma for the gathering in sept.


i'd offer to drive it to haibecks from the st louis area, going
up there to pick mine up, in a couple of weeks.
if you are pressed for time.

good luck

Keith

[scottfab]

Not always true, sometimes the coil will fail on an individual tower. I've seen it a couple of times.

Technically impossible but I suppose ther could be something I don't understand about the failure that would have such a symptom.
I'd sure like to get a hold of one that fails on just one side.
You may have not seen the failure but I wonder if it wasn't still failing?
Or maybe one of the two ignition wires was arcing to ground.

Each of the four coils fire on two plugs at the same time.
Once on compression and once on exhaust stroke. If one plug is very fouled it may not show spark at all and the other will. Next time you see what you think is "one tower" fireing. Try unplugging both sides and place a known good plug in each and ground the outside of each plug. The spark on each should be the same even if the coil is failing. The trick is to compare a good coil to a bad one. Depending on how bad the coil is you'll see a marked difference. Best check I've seen on the net was measuring the secondary coild resistance when the coil is hot. With wires disconnected it will be about 5.7 ohms acording to my notes.

[Jeffvette]

I've stumbled on it twice. Spark is nice and strong on one side, and weak or non existent on the other side. Not sure if it's corrosion issues inside the tower. Next time I get one I'll save it for you to dissect.



Greg, any update?

[GregCrowe]

I've stumbled on it twice. Spark is nice and strong on one side, and weak or non existent on the other side. Not sure if it's corrosion issues inside the tower. Next time I get one I'll save it for you to dissect.



Greg, any update?

Just got the coils in Monday. If I can find some time this weekend, I'll change them. Time is the problem though.

[GregCrowe]

Put the coils on Sunday, now the car runs even worse. I'm so disgusted.

I need to rip it all apart and see if I goofed something up. Now the car starts up and idles just fine. When in park, giving it gas makes it rev slowly with hesitation. I even got it to backfire once. I took it out for a drive and it just felt down on power, engine didn't run smooth, slight stumble all the time. I never even got the car hot enough to see if the original problem was still there. I don't know that I could have even told.

[XfireZ51]

Put the coils on Sunday, now the car runs even worse. I'm so disgusted.

I need to rip it all apart and see if I goofed something up. Now the car starts up and idles just fine. When in park, giving it gas makes it rev slowly with hesitation. I even got it to backfire once. I took it out for a drive and it just felt down on power, engine didn't run smooth, slight stumble all the time. I never even got the car hot enough to see if the original problem was still there. I don't know that I could have even told.

Forgive me but are
plug wires on correctly?

[GregCrowe]

Forgive me but are
plug wires on correctly?

I'm sure they are, I did one coil at a time. The car starts and idles smoothly.

If I can find some time, maybe this coming weekend, I'm going to take it apart and see if I messed anything up. If I don't find anything wrong, I'm going to go buy a set of the cheapest coils at O'Reilly and put it back together. My worry now is that I'm going to have to take it apart 5 more times to test things and find out what's wrong.

Dumb question: Is there any way to put the long electrical connector on the bottom of the plenum(held in with the screw), in 180 degrees off?

Not so dumb question: How do you test the coils with a volt meter ?

[tomtom72]

Okay fwiw the description of how it runs reminds me of what used to happen back in the days of distributors. If ya missed a coupla teeth on the way back in the motor usually ran as you describe. Or...a more ominious thought just crossed my mind, skipped teeth on the timing gear set, but I don't think that applies to an LT5, I hope.

Disclaimer: I'm okay with a 70's sbc, I'm not fluent in LT5 yet.

My first impression was exactly what XfireZ51, miss placed plug wires. I can go look up the firing order in my Helm if need be? See I told ya I'm not fluent in LT5, heck I don't even remember the firing order on my 72 LT-1 that I had a long time ago (I'm also getting senile!).

I would wonder if a scan tool would diagnoise a problem with the DIS box? That's the only other thing I can think of, unless there is a insulation problem with the harness that connects the coil plate to the DIS box? Can the plate go bad?

I shouldn't even post this as I'm lost on diagnoising your issue.:o

:cheers:
Tom

I know you don't want to hear this Greg, but simplest things first. Firing order, bridged plugs, wires okay, coils seated properly, DIS wiring I believe is "Keyed" so you really can't put individual harnesses in the wrong spots or 180* off (I'm fairly sure on that point). I know there used to be a lot of defect issues with aftermarket coils a long time ago the experienced guys said to stay with GM coils. That's all I can think of right now. Sorry for my lack of help.

[Jeffvette]

Dumb question: Is there any way to put the long electrical connector on the bottom of the plenum(held in with the screw), in 180 degrees off?

Greg, I would double check the plug wire orientation. I always label the plug wires with either collars or paint.

Also check the DIS module for a possible bent pin. And no, you can not install the connector 180 off. It is keyed to go in one way only.

[GregCrowe]

Sunday is my only day I have a few hours I can work on my own car. I just took it apart again. Here's some pics.

Jeff, take a look at the pic of the DIS module. This is with the plenum laying upside down. Can you please tell me if any of the pins are missing? It looks fine to me. Given that you're looking at the module mounted to the plenum and the plenum is upside down, there is 7 slots for pins, the screw, and then 7 more slots for pins. Looking at the pic, the pins slots are as:

1. empty
2. empty
3. empty
4. pin
5. pin
6. pin
7. pin
SCREW
1. pin
2. pin
3. pin
4. pin
5. pin
6. empty
7. pin

Here's the confusing part:

Looking at the DIS module, there are 4 pins in the first set of 7 slots and 6 pins in the second set of 7 slots.

Looking at the DIS modue connector, there are only 4 electrical female slots on each side for the pins in the module. It doesn't match up...... 6 pins and 4 female slots for those 6 pins on the right side. Do I take it that 2 of those pins on the right side are just there for no reason and not used?

I don't think I have a broken or bent pin. I really don't see anything wrong.

Also, I double and triple checked the plug wire orientation. It is all correct.

http://www.rpmmotorsportstulsa.com/Greg/DIS.jpg
http://www.rpmmotorsportstulsa.com/Greg/DIS2.jpg
http://www.rpmmotorsportstulsa.com/Greg/Coils1.jpg
http://www.rpmmotorsportstulsa.com/Greg/Coils2.jpg

[Jeffvette]

Sunday is my only day I have a few hours I can work on my own car. I just took it apart again. Here's some pics.

Jeff, take a look at the pic of the DIS module. This is with the plenum laying upside down. Can you please tell me if any of the pins are missing? It looks fine to me. Given that you're looking at the module mounted to the plenum and the plenum is upside down, there is 7 slots for pins, the screw, and then 7 more slots for pins. Looking at the pic, the pins slots are as:

1. empty
2. empty
3. empty
4. pin
5. pin
6. pin
7. pin
SCREW
1. pin
2. pin
3. pin
4. pin
5. pin
6. empty
7. pin

Here's the confusing part:

Looking at the DIS module, there are 4 pins in the first set of 7 slots and 6 pins in the second set of 7 slots.

Looking at the DIS modue connector, there are only 4 electrical female slots on each side for the pins in the module. It doesn't match up...... 6 pins and 4 female slots for those 6 pins on the right side. Do I take it that 2 of those pins on the right side are just there for no reason and not used?

I don't think I have a broken or bent pin. I really don't see anything wrong.

Also, I double and triple checked the plug wire orientation. It is all correct.


Pins look fine on the DIS module. And yes there are only 8 active connections on the DIS. 4 wires going in on each side of the bolt/screw.


I'm still thinking you have a spark issue, and it's cutting out.

[GregCrowe]

Pins look fine on the DIS module. And yes there are only 8 active connections on the DIS. 4 wires going in on each side of the bolt/screw.


I'm still thinking you have a spark issue, and it's cutting out.

OK, thanks Jeff. Since it got worse with the new Summit coils I'll go pick up some coils from O'Reillys and slap them on. If that fixes it I'm going to have a pretty upset conversation with Summit Racing.

[XfireZ51]

OK, thanks Jeff. Since it got worse with the new Summit coils I'll go pick up some coils from O'Reillys and slap them on. If that fixes it I'm going to have a pretty upset conversation with Summit Racing.

Greg,

Have you checked plug wires? Meaning have you checked for open circuit or ohm's them?

[GregCrowe]

Greg,

Have you checked plug wires? Meaning have you checked for open circuit or ohm's them?

They have less than 20 miles on them. That was the first thing I tried almost 3 years, new plugs and wires. The car did the exact same thing before and after the plug/wire change.

[GregCrowe]

Jeff, is there anything special about the ZR1 coils? Are all these GM DIS coils the same?

edit: I'm finding that most all GM cars with DIS systems use the AC Delco D555 coil. For some reason, the ZR1 is listed as using the D545 which seems to be ZR1 specific. This has me suspecting the Summit Coils or any other standard coils may be a problem ??? But then again, just found another webpage with a GM replacement coil(Chinese like all the cheapies at Auto Zone and OReillys) saying it replaces BOTH the D555 and D545. I'm confused.

http://www.rmsautoparts.com/proddetail.php?prod=D545

http://www2.partstrain.com/store/?Ntt=+ACD545&AID=10474942&PID=3055586&SID=1&cj=1

http://www.amazon.com/gp/product/B000C9TWHQ/?ie=UTF8&me=A8F3HAQ1FDLH8

Further investigation finds the Accel coil:

http://www.car-stuff.com/store/images/prodimage/thumbs/accel/140017.jpg

Summit coil as shown on Summits website:

http://static.summitracing.com/global/images/prod/large/sum-850017_w.jpg

Summit coils they sent me:

http://www.rpmmotorsportstulsa.com/Greg/Coils1.jpg

Notice how the coils Summit sent me don't match the pic on their website. Also notice that the Summit coils sent to me are exact copies of the Accel coils. The body is the exact same and these are the only versions that look like this. They also both have the gold terminals and both have the little side tabs that have to be ground off. Jeff, aren't you using the Accel coils? I'm 99% positive the Accels and Summits sent to me are the same thing.

Further edit: Sherlock Holmes scores........

BUSTED ! For sure the Summit coils sent to me ARE ACCEL COILS !
Notice the part number on the side of the Summit boxes: SUM-850017
Part number listed for the Accel coils : ACC-140017 http://www.accel-ignition.com/ProductDetails.aspx?modelNumber=140017&productID=6493&majID=505&minID=5052&selection=0&minselection=1

[GregCrowe]

I may not be doing this right so please correct me if I'm not but I measured the resistance on the stock coils at the 2 spark plug wire terminals. This is what I got:

1. 5.71 k-ohms
2. 5.61 k-ohms
3. no reading
4. no reading

Then I did the Summit/Accel coils:

1. 7.18 k-ohms
2. 7.24 k-ohms
3. 7.20 k-ohms
4. 7.26 k-ohms

Jeff, what does this mean to you ?

[tccrab]

1. 5.71 k-ohms
2. 5.61 k-ohms
3. no reading
4. no reading

Jeff, what does this mean to you ?

While I am no JeffVette, it looks to me like you've found something.
Providing that you measured the coils exactly the same way, i.e., where you touched the contacts with the meter pins, then it would appear that coil pack 3 and coil pack 4 have gone open circuit.
Assuming that these coil packs are not functional or perhaps only marginally operational, you would have the worlds worst running 4 cylinder engine.

TomC
"Crabs"

[GregCrowe]

While I am no JeffVette, it looks to me like you've found something.
Providing that you measured the coils exactly the same way, i.e., where you touched the contacts with the meter pins, then it would appear that coil pack 3 and coil pack 4 have gone open circuit.
Assuming that these coil packs are not functional or perhaps only marginally operational, you would have the worlds worst running 4 cylinder engine.

TomC
"Crabs"

Yes, that's what I thought. I definitely don't have a 4-cylinder ZR-1. The car was(before the Summit coils) running fine when cold. I was shocked to not be able to get a reading from 2 of the coils. I must have went back 10 times and tried to get readings from them. Every single time, nothing. I suspect they must be marginal. Why the Summit coils made the car run like crap I still have no clue.

I'm waiting for Jeff to chime in but I'm thinking about going and buying 4 of the GM D545 coils.

[XfireZ51]

Greg,

Have you tried ohm'ing the coils from the positive and ground inlets at the bottom of the coils? The original Summit coils you showed look VERY MUCH like the MSD coils I have without the lettering. However all that doesn't explain why the stock coils still would produce a hesitation on acceleration. :confused:

[GregCrowe]

Greg,

Have you tried ohm'ing the coils from the positive and ground inlets at the bottom of the coils?

I tried but couldn't get my volt meter terminals to fit up in the slots and get any kind of a reading. I might try sticking some wires up there tomorrow and read off the wires.

[Jeffvette]

I may not be doing this right so please correct me if I'm not but I measured the resistance on the stock coils at the 2 spark plug wire terminals. This is what I got:

1. 5.71 k-ohms
2. 5.61 k-ohms
3. no reading
4. no reading

Then I did the Summit/Accel coils:

1. 7.18 k-ohms
2. 7.24 k-ohms
3. 7.20 k-ohms
4. 7.26 k-ohms

Jeff, what does this mean to you ?


Connect the ohmmeter leads across the ignition coil primary terminals, and compare the primary resistance reading to specifications (GM asks for .35 - 1.45 OHMS). Then connect the ohmmeter leads across the coil secondary terminals and compare the secondary resistance reading to specifications (GM asks for 5,000-6,500 ohms).

Any replacement coil must be within the spec of the primary terminal.

GM does call out two different DIS coils. D545 and D555. The D545 is what they consider a replacement in the LT5. I would suspect that the aftermarket does make coils that are all inclusive. Check the primary readings and let us know what you find.

[GregCrowe]

When you say "primary reading", do you mean from the 2 little slots on the bottom of each coil ?

[Jeffvette]

Yes

[XfireZ51]

When you say "primary reading", do you mean from the 2 little slots on the bottom of each coil ?

Greg,

Try fitting some spade lugs in the slots and then connecting Ohmeter to them.

[GregCrowe]

Greg,

Try fitting some spade lugs in the slots and then connecting Ohmeter to them.

Spades wouldn't even fit up in those tiny slots. I did however use some wires.

Testing of the original GM coils got me:

Primary / Secondary
1. .6 ohms / 5.63 k-ohms
2. .6 ohms / 5.57 k-ohms
3. .6 ohms / zero
4. .6 ohms / zero

All the stock coils look fine on the primary readings. The secondary readings do look suspect.

I'll try to pull the Summit/Accel coils and get a primary reading on them today if possible.

[GregCrowe]

I bought a set of brand new GM ZR-1 D545 coils.

So.........More coils, more tests:

Summit/Accels :

Primary / Secondary
1. .7 ohms / 7.02 k-ohms
2. .6 ohms / 7.06 k-ohms
3. .6 ohms / 7.06 k-ohms
4. .7 ohms / 7.00 k-ohms

Brand New GM D545's

1. .5 ohms / 5.71 k-ohms
2. .5 ohms / 5.64 k-ohms
3. .5 ohms / 5.66 k-ohms
4. .5 ohms / 5.66 k-ohms

The one thing I did notice on the Summit Accel coils was that the slots on the bottom of each coil(that the 2 spade terminals plug into) were bigger and more loose than on the GM coils. They definitely don't make a nice tight connection. That may be the problem.

I should have the car back together tomorrow and we'll see if it's fixed.

[GregCrowe]

IT'S FIXED !!!!!!!!!!

Yes folks, my ZR-1 is running like a champ again. New GM D545 coils fixed the problem. The high rpm power is awesome. No cutting out, no miss, no falling on it's face.

For the record, let it be know that SUMMIT/ACCEL COILS SUCK !!!!!!

These are absolute JUNK !

http://www.rpmmotorsportstulsa.com/Greg/Coils1.jpg

I will be having a nice conversation with Summit tomorrow.

I would like to thank everyone out here for their help over the past 3 years and especially JeffVette.

[Jagdpanzer]

Congratulations Greg!!
The entire ZR-1 brotherhood applauds you!
Your perseverance, determination, and resourcefulness have finally paid off.
34 months, 173 posts, 8,600 looks later and the problem is now solved
....and at the end you got it right about the coils.
I almost picked up a set of Accels a while back for spares but went with the MSD 8224's instead. Just checked them and they meg out the same as your new set of GM D545's.

[Jeffvette]

IT'S FIXED !!!!!!!!!!

Yes folks, my ZR-1 is running like a champ again. New GM D545 coils fixed the problem. The high rpm power is awesome. No cutting out, no miss, no falling on it's face.

For the record, let it be know that SUMMIT/ACCEL COILS SUCK !!!!!!

These are absolute JUNK !



I will be having a nice conversation with Summit tomorrow.

I would like to thank everyone out here for their help over the past 3 years and especially JeffVette.

Glad to hear Greg. Go and give summit hell.

[gbrtng]

Is the LT5 coil a common GM part?

[GregCrowe]

Is the LT5 coil a common GM part?

Very common. GM D555 or D545. I have no idea what the difference is between the 2 part numbers. It's the same coil as used on almost every GM V6. 3 coils on the V6, 4 on the ZR-1 V8.

[GregCrowe]

I may have figured out the difference between the GM D545 vs the GM D555 coil. The D545 lists for 70 cents more than the D555. It looks like the D545 comes with a little rubber gasket a hair over an inch long that goes around the 2 pin connectors under the coil. From best I can tell, the D555 comes without the rubber gasket.

[GOLDCYLON]

Damn awesome !! Makes me feel better I changed out mine with GM replacements as well when I had the top end done. Damn gald to hear you chased that problem down!! I considered going the Summit route as well

[tccrab]

Good Job Greg!
:thumbsup:
I commend you for your perseverance.
:worship:
I personally would have given up hope after only a month or two, but you've hung in there for nearly 3 long years.
Simply Amazing.

Now, get in it and.....

DRIVE IT LIKE YOU STOLE IT!!!

Congratulations, my hat is off to you.
Long live the beast.

TomC
"Crabs"

[Zr1 Destroyer]

:occasion1:occasion1:occasion1:occasion1:occasion1 :occasion1

[tomtom72]

Good deal Greg! :thumbsup:

You wouldn't happen to have the part number for the GM coils?

TIA
:cheers:
Tom

[GregCrowe]

Good deal Greg! :thumbsup:

You wouldn't happen to have the part number for the GM coils?

TIA
:cheers:
Tom

D555: 10472401
D545: 10467067

Here's a great deal on the D555's:

http://cgi.ebay.com/ebaymotors/NEW-GM-IGNITION-COIL-Cavalier-Impala-Camaro-D555-D-555_W0QQcmdZViewItemQQcategoryZ33689QQihZ022QQitem Z350175057440QQrdZ1QQsspagenameZWDVW

[tomtom72]

Thanks Gregg!:thumbsup:


:cheers:

[bobbyhi]

Glad you got the Z running again:dancing.

I had a similar problem with mine. I switched to the Accel coils and the car wouldn't run very well when hot. I took it to DRM and Doug said that the Accels would fail because of the heat generated by the engine. He replaced with GM coils and the car ran just fine after that. Unfortunately that didn't solve my other problems but that's another story.:mrgreen:

[scottfab]

Greg, sure glad you nailed it and really glad you hung onto the car.
I am curious about the Summit coils. Did they take them back?
What size wires are you using? 7mm or 8mm?
Since the summit coils were not subjected to high temperatures I am curious about the failure mechanism. If the primary to secondary winding ratio is large enough over stock then the secondary voltage could be exceeding the insulator breakdown voltage of the wire insulation.
(hotter spark)
The measured resistance seems to indicate this but there are other explanations behind the measured values. (quality and diameter of wire)
I sure would like to cut one of those summit coils apart.
Root cause analysis stuff.
Thanks
Scott

[GregCrowe]

Greg, sure glad you nailed it and really glad you hung onto the car.
I am curious about the Summit coils. Did they take them back?
What size wires are you using? 7mm or 8mm?
Since the summit coils were not subjected to high temperatures I am curious about the failure mechanism. If the primary to secondary winding ratio is large enough over stock then the secondary voltage could be exceeding the insulator breakdown voltage of the wire insulation.
(hotter spark)
The measured resistance seems to indicate this but there are other explanations behind the measured values. (quality and diameter of wire)
I sure would like to cut one of those summit coils apart.
Root cause analysis stuff.
Thanks
Scott

Yes, Summit took them back. I'm using new GM plug wires, think they're 8mm. I think the problem with the Summit/Accel coils was the 2 connection slots. They were too lose, didn't squeeze the terminals that plugged into them.

[scottfab]

Yes, Summit took them back. I'm using new GM plug wires, think they're 8mm. I think the problem with the Summit/Accel coils was the 2 connection slots. They were too lose, didn't squeeze the terminals that plugged into them.

Ok that makes sense. Good detective work. I put Accel coils in back in mid 2002 and have not had an issue. As I wrote earlier I did have a similar issue to yours with the stock ones but I believe two of them were defective (a few shorted windings) because they read lower resistance on the seconaries than the rest. One thing I did have to do was replace the stock wires with 8mm because they began arcing through the insulation with the Accels. I do remember having connection issues with the new coils on the input because they came with an orange rubber like gasket. The problem was some of the plugs on the wireing harness had the orange gasket still attached. That made for two gaskets and it would not make a proper connection.
Anyway, we're all glad I am sure that you're back on the road. Good timing too. Summer is knocking at the door.=D>

[ZR1North]

D555: 10472401
D545: 10467067

Here's a great deal on the D555's:

http://cgi.ebay.com/ebaymotors/NEW-GM-IGNITION-COIL-Cavalier-Impala-Camaro-D555-D-555_W0QQcmdZViewItemQQcategoryZ33689QQihZ022QQitem Z350175057440QQrdZ1QQsspagenameZWDVW

What a great thread!

I pursued Greg's tip and purchased the "D555s" noted above, but I am not sure I want to install them now that I have them.

On these new units, the secondary windings are measuring 5.6 to 5.8K which is close to the GM recommended range of 5.6 to 5.7, but the primary windings are measuring 1.7 ohms - GM recommendation is .5 ohms. I am also a little suspecious of the part no on the replacements; it is 10482928 rather than the numbers Greg quoted above. I am thinking - don't think I will use these replacements. Am I being too cautious?

[Jeffvette]

What a great thread!

I pursued Greg's tip and purchased the "D555s" noted above, but I am not sure I want to install them now that I have them.

On these new units, the secondary windings are measuring 5.6 to 5.8K which is close to the GM recommended range of 5.6 to 5.7, but the primary windings are measuring 1.7 ohms - GM recommendation is .5 ohms. I am also a little suspecious of the part no on the replacements; it is 10482928 rather than the numbers Greg quoted above. I am thinking - don't think I will use these replacements. Am I being too cautious?


Another too good to be true? Those are half the cost of AC delco direct from delco.

[ZR1North]

What a great thread!

I pursued Greg's tip and purchased the "D555s" noted above, but I am not sure I want to install them now that I have them.

On these new units, the secondary windings are measuring 5.6 to 5.8K which is close to the GM recommended range of 5.6 to 5.7, but the primary windings are measuring 1.7 ohms - GM recommendation is .5 ohms. I am also a little suspecious of the part no on the replacements; it is 10482928 rather than the numbers Greg quoted above. I am thinking - don't think I will use these replacements. Am I being too cautious?

I LIKE JERRY'S REPONSE TO MY QUESTION. I'D BE INTERESTED TO KNOW IF ANYONE ELSE HAS SOME WISDOM TO ADD TO THIS - APPRECIATED!

JERRY'S RESPONSE:

CAVEAT: I'm no expert on the subject but think I understand the principal according to the following tech article.

Transformers/Ignition coils

Transformers step-up (increase), step-down (decrease), or pass-through (same level) AC voltage or pulsed DC voltage. A basic power rule applies to transformers; power-in equals power-out. The unit of measure for Power is the Watt. 1 Watt = 1 Volt x 1 Amp.

A transformer has three main components:

An iron core - The iron core is wrapped with two separate coils of wire. The job of the iron core is to strengthen the magnetic fields of the transformer.

Primary winding - The input side of the transformer. This coil of wire is tightly wrapped around the iron core of the transformer.

Secondary winding - The output side of the transformer. This coil of wire is tightly wrapped around the primary winding of the transformer.
There are three basic types of transformers:

Step-up transformer - The primary coil winding has less windings of wire than the secondary coil does. A 1:2 step-up transformer has half as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 24 V AC will be induced into the secondary winding, however, the output amperage will be cut in half to 6 amps.

Step-down Transformer. - The primary coil winding has more windings of wire than the secondary coil does. A 2:1 step-down transformer has twice as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 6 V AC will be induced into the secondary winding, however, the output amperage will be doubled to 24 amps.

Pass-through transformer - In a 1:1 transformer, the primary coil winding has just as many windings of wire as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 12 V AC will be induced into the secondary winding, and the output amperage will be 12 amps. The advantage of a 1:1 transformer is that there is not a direct electrical connection between the two coils. If one side of the circuit gets short circuited, the other side will remain isolated.

Examples of transformer use on automobiles:

Ignition coils - An ignition coil is an example of a step-up transformer, the primary coil input voltage is 12-15 V and the secondary output voltage is 20-60 kV. This means for every primary coil winding there are at least 2000 secondary windings. This also means that the output amperage will be at least 2000 times smaller than the input amperage. Secondary ignition voltage is high voltage, but amperage is low.


Quote:
.....the primarly windings are measuring 1.7 ohms vs the .5 ohms specified by GM. The secondary windings seem ok (the new ones are measuring 5.6K to 5.8K which is close to the 5.6-5.7K quoted by GM).

Since only resistance is known and number of windings is unknown, I assume that winding wire size & type is the same, therefore resistance is a function of length of wire in the windings.

I interpret your findings to show that the resistance of the primary windings in the eBay coil is 3.4 times that of the OEM LT5 coil, meaning it has more windings. If the resistance of the primary windings is higher and the secondary windings resistance is the same, that means the voltage output would be lower than the OEM LT5 coil, i.e. coil discharge voltage is not as high as the OEM LT5 coil.

My non-expert opinion, don't use them. The spark is not as hot.

However, I do have my flame suit on!http://images.ibsrv.net/ibsrv/res/src:forums.*************.com/get/images/smilies/lol.gif END OF JERRY'S TAKE

[scottfab]

Generally I’d have to agree with the functional description of a transformer entered. However, there are a few assumptions that cannot be made. Some matter some don’t. The core of the transformer may not be iron. It’s probably a composite ferrite. That does not matter.
But to assume the diameter of the primary wire is the same as the GM part may be a mistake. Assuming this was done on purpose as a method of increasing reliability it may be that a smaller diameter wire was used. This would make it possible for the manufacturer to use the same number of windings but draw less power. Less power would mean less heat internally. Less heat at the windings could translate to fewer shorts between windings. This is pure speculation on my part but I’d guess the higher primary winding resistance was done on purpose.

Generally using winding resistance is a poor way of judging coil quality. While differential resistance between like type parts is better than nothing a truer measure would be output voltage swing measurements. And what’s more doing this measurement while the coil is at high temperature would be a great test. I am not sure of what the major failure component would be on these coils but I am guessing either internal shorts OR high voltage arching internally. An internal arching problem is not likely to show up on a static resistance measurement.

What I’ve read about the Summit and Accel coils on this thread does not confirm to me that they are bad. If the primary connectors were not pinching the spade end of the car’s connection addequately that is easily fixed my squeezing them together before assembly. Such a failure does not mean the coil cannot produce the needed output voltage. Of key importance on these coils is longevity at the temperatures in the engine valley that the LT5 has.

I’d sure like to get my hands on a coil that fails. Even better, one that reportedly fails on only one side. That is, each coil sparks two cylinders each time if fires. (one is on exhaust stroke the other on compression) On a failure such that only one side fails it should be possible to swap the two plug wires right at the coil and see the failure move to the other cylinder. Yah, that would be a lot of plenum work :icon_scra

[GregCrowe]

Another too good to be true? Those are half the cost of AC delco direct from delco.

Yes, I found out this guy up East is misrepresenting these coils as new. They are just take-offs from who knows what. I bought a set from him and promptly sent them back when I found out what he was doing.

The coils I installed on the car were real new GM D555's in GM boxes from O'Reilly Auto Parts.

[A26B]

......But to assume the diameter of the primary wire is the same as the GM part may be a mistake.

:dontknow:You gotta make some assumptions somewhere as a starting point or it's going to turn into a book no one wants to read. I think you even made an assumption:dancing