Knowledgeable Tech -Starting/Performance problem needing assistance

[sjs]

Hello everyone, I am new so please bear with me. I am new to the forum and this is the first zr-1 I have owned (90 model w/100k). Bought it last year, runs pretty good but secondary actuator does leak. I am an engineer but hate to admit I haven't bought a service manual yet (toys never break do they? LOL) Anyway, drove it for about 3k miles last year, wife drove it the first day of spring and as she turned in the drive it ran rough and died. Would start and run, but sounded and smelled flooded - would start after it dried out ... but would die. Put it in clear flood mode and will start but runs tough for a few seconds and dies. It used to start wonderful and run hard .. now it is becoming an annoyance and a reluctant wife is starting to loose faith and trust in her first vette. So if anyone has any ideas I would love to hear from the people who know the most about them. When it does run it pulls 11in of very steady vacuum at a low/rough idle , I thought it sounded throaty but funny (faint popping through the intake (had filter out), and tested fuel pressure at 39 psi (it does hold pressure too). So I am at a loss for what its malfunction is as I am NOT heavily familiar with this engine - not near as well as an l98 i used to have in a trans am. Could this exotic 4 cam engine have a jumped cam as they are known to have tensioner problems? But why does it have steady and almost good idle vacuum? Bad injectors ? But why will it run good for a few seconds before going down and why do the hold pressure (ie not leak), Scanner showed only lean code and secondary actuator code (i assume from its slow secondary vacuum leak) ... So I assume spark and ecm are okay since it kinda runs ....

Anyway, LT5 experts ..... please help and thanks in advance.
sjs

[Z51JEFF]

Since the injectors are the first thing to fail I would look at those first.No trouble codes,check engine light?Regardless the problem is not a major one,these motors are not known for breaking.

[A26B]

While I do agree completely with Z51Jeff, regarding the need to ultimately replace original injectors, especially for 90~92 models, I would also suggest the following posibility that can be easily checked & remedied if necessary.

One of the more common ocurrences is a MAP sensor hose that has come loose. The LT5 with its waste spark system, requires that during starting, the key is held in the start position momentarily after the engine starts. Otherwise, on ocassion, the engine will backfire and the suden manifold pressure will blow the connector hose (plenum to MAP sensor) off.

Here is a photo showing the placement of the MAP Sensor hose.

http://i190.photobucket.com/albums/z224/A26B/MAPSensorHose.jpg

[gbrtng]

When my 91 sneezes and blows off the MAP hose it sets an SES code and light.

sjs: does it set any SES codes?

[tccrab]

At 100k miles I'm willing to be that it's already had the injectors replaced.
That being said, it could still be bad injectors, especially if the previous owner had them replaced with more of the Multecs.
Check the MAP hose first as Jerry said above.
Maybe one of the Brotherhood local to you wouldn't mind meeting with you for a semi-educated diagnosis.
:cheers:

TomC
'Crabs

[Jagdpanzer]

Where abouts in Kansas are you located?
I grew up in Garden City, KS and now live in Northern Virginia.

[Kb7tif]

Hello everyone, I am new so please bear with me. I am new to the forum and this is the first zr-1 I have owned (90 model w/100k). Bought it last year, runs pretty good but secondary actuator does leak. I am an engineer but hate to admit I haven't bought a service manual yet (toys never break do they? LOL) Anyway, drove it for about 3k miles last year, wife drove it the first day of spring and as she turned in the drive it ran rough and died. Would start and run, but sounded and smelled flooded - would start after it dried out ... but would die. Put it in clear flood mode and will start but runs tough for a few seconds and dies. It used to start wonderful and run hard .. now it is becoming an annoyance and a reluctant wife is starting to loose faith and trust in her first vette. So if anyone has any ideas I would love to hear from the people who know the most about them. When it does run it pulls 11in of very steady vacuum at a low/rough idle , I thought it sounded throaty but funny (faint popping through the intake (had filter out), and tested fuel pressure at 39 psi (it does hold pressure too). So I am at a loss for what its malfunction is as I am NOT heavily familiar with this engine - not near as well as an l98 i used to have in a trans am. Could this exotic 4 cam engine have a jumped cam as they are known to have tensioner problems? But why does it have steady and almost good idle vacuum? Bad injectors ? But why will it run good for a few seconds before going down and why do the hold pressure (ie not leak), Scanner showed only lean code and secondary actuator code (i assume from its slow secondary vacuum leak) ... So I assume spark and ecm are okay since it kinda runs ....

Anyway, LT5 experts ..... please help and thanks in advance.
sjs


You have come to correct place.

[sjs]

Where abouts in Kansas are you located?
I grew up in Garden City, KS and now live in Northern Virginia.

We are up in the northeast corner by Manhattan KS, GO KSU!

[sjs]

THANKS TO EVERYONE FOR THE ADVICE .... !!!!

Just an update and to answer some questions, I did check the MAP sensor and hose, but thanks everyone who mentioned it as it is very important. Unfortunately it reads okay and correctly on the scan tool (MAP and BARO) ... I even tried to fake the motor our with a hand vacuum pump on the sensor, car still starts and runs the same, runs for a few seconds then loads up and dies. Also like I said earlier then only 2 codes are lean and secondary operation, other than that it is clean. Plan to work on the secondary actuators, but have to know what is wrong with the rest of the motor before pulling the plenum off. Does anyone know what pulse with should be on a 70deg day? Mine runs about 7.5 ms .... wondering if that is normal >>?????? If it is may just be junk injectors .... just thought it strange that they are bad but don't leak down at all ??@#$@???? I would think the spray would have to be just awful to make it run this bad. You can squirt raw gas in the intake manifold and make it run better than it is right now! Low crank and idle vacuum still concern me a little ... does anyone know what a ZR-1 should have for crank vacuum and idle vacuum ??? ARE THEY SPECIAL or the same as a L98 or LB9? Again thanks all for the expert help

[zr1don]

Idle vacume should be 18 - 20 in, inj pw at idle should be around 4 ms, idle fp should be around 46, 39 is definitely low.

[zr1don]

If the 11 in "vacume" you referenced is the MAP sensor reading at idle, that is normal, something around 18+ in of idle vacume.

[sjs]

Idle vacume should be 18 - 20 in, inj pw at idle should be around 4 ms, idle fp should be around 46, 39 is definitely low.

Thanks, you don't happen to know about cranking vacuum and ms do you ?:cheers:

[sjs]

Thanks ZR1Don for the info, no the reading is 11in of guage vacuum not scanned ... although this was at a rough idle seconds before it died. I am starting to wonder again about cam timing slippage, but I suppose I had better check my injectors first ... just hate to take the motor apart twice! Also sorry about the spelling, the later it is the worse my spelling is !
Thanks for the help.

[Paul Workman]

At 100k miles I'm willing to be that it's already had the injectors replaced.
That being said, it could still be bad injectors, especially if the previous owner had them replaced with more of the Multecs.
Check the MAP hose first as Jerry said above.
Maybe one of the Brotherhood local to you wouldn't mind meeting with you for a semi-educated diagnosis.
:cheers:

TomC
'Crabs

BINGO!

That is what happened on mine. The injectors were replaced with more of the same (GM dealership before I bought it). They crapped again as well. The new Accels made and incredible difference in overall operation, and especially at idle!

And too, as pointed out, the fuel pressure situation has to be resolved first. That issue alone can be the root of a lot of evil.

To the OP: the O2s are not going to come into play until the thing warms up some, but once you get to that point where it goes into "closed loop" mode, you might want to compare integrator values and O2 cross-points. First thing tho...is that fuel pressure issue!

P.

[lbszr]

Was the fuel pressure monitored while it was trying to run, or with the key on? It might be falling even lower than 39 while it's running.

[sjs]

BINGO!

That is what happened on mine. The injectors were replaced with more of the same (GM dealership before I bought it). They crapped again as well. The new Accels made and incredible difference in overall operation, and especially at idle!

And too, as pointed out, the fuel pressure situation has to be resolved first. That issue alone can be the root of a lot of evil.

To the OP: the O2s are not going to come into play until the thing warms up some, but once you get to that point where it goes into "closed loop" mode, you might want to compare integrator values and O2 cross-points. First thing tho...is that fuel pressure issue!

P.




Thanks, am working on the fuel psi right now ... will let everyone know

[Kevin]

you can check if the injectors are good with an ohm meeter. good ones should be between 12.5 and 15 ohms

[sjs]

Well, I did learn the why the psi was a little low ... fuel filter wasn't that old but it was restricted some ... also pulled the pumps to see if they were both okay and found a cracked hose ... not bad but cracked. This did help the psi and it stays steady at 48 psi at all times. So this is good news, easy fix ...!!!

Now for the bad news , injectors still don't leak down but car still won't really run. I don't have to worry about closed loop or cross counts ... car wont stay running over 30 seconds ... period. Will restart but dies again.... am going to have to assume the injectors are bad as everyone mentioned them ... only thing that bothers me is that I have seen cars with 2-3 bad injectors run better than this ... I have a hard time buying 3-4 went bad all in the same 5 min trip ?? But you never know ... will replace them and see if it runs ... if it doesn't my ZR-1 experience may not be a good one! But either way I sure like the car ... just frustrating as I don't have time right now for major surgery .... wife's daily driver has needed a wrist pin for 6mo now .... no way she will like tearing this down first if the injectors don't cure it. Hope they do! Thanks to all for the advice!

[Paul Workman]

... injectors still don't leak down but car still won't really run. I don't have to worry about closed loop or cross counts ... car wont stay running over 30 seconds ... period.

only thing that bothers me is that I have seen cars with 2-3 bad injectors run better than this ... I have a hard time buying 3-4 went bad all in the same 5 min trip ??

Yeah...I'm dubious too, far as injectors causing this severe of a problem goes. Sounds like we need to put the anecdotal suggestions in their place and begin with the basics; a methodical elimination process.

Note: When it's time to get down to brass tacks...like now...I always like to establish a solid base - deductive reasoning, if you will - working toward discovery in a logical, progressive manner. Its sort of like painting a wall by beginning at one end and working toward the other instead of a random swipe with a brush first here and then there until the wall is covered.

However, by reading the posts for a few years, my unscientific survey says 90% of the LT5 gremlins reside under the plenum: The problems seem to center around (1) the OEM injectors, (2) secondaries, (3) starter solenoid contacts, and (4) coil packs...in that general order. Address them all while under the plenum on the first visit and one can be very confident of the LT5 after that for some time to come. So, I sometimes chose to R&R certain things just to head off potential near-term problems - regardless of whether they are causing the current problem or not; I'd rather be driving than wrenching, if you know what I mean.

A preliminary question: Water in the fuel? That is worth eliminating before going on...Just a thought. (We had that issue here locally with one of the Shell stations last winter. Messed up a bunch of cars here in town for a week or so till the problem was discovered and rectified.)

At this point I would like the peace of mind that she's not suffering a mechanical malady. A compression check would clear the air - far as a gasket or cam timing goes. And, we get to look at all the plugs for clues in the process!

With all the plugs pulled and having a fully charged battery and a full blown battery charger on the battery (i.e., no trickle charger, but one capable of maintaining full charge between cylinder tests), and having the accelerator to the floor (anti-flooding mode kills power to the injectors when rpm is below normal idle speed), crank it for 5 compression strokes (rest of plugs removed) and see what it reads. For comparison, compression on my LT5 was 180# at one time, and after my porting and cam re-timing it was 220, FWIW. Uniformity (w/in say range of 10#) from cylinder to cylinder and side to side, being the point. And, apparently compression can range between 180 and 220#, depending on circumstances.

I'm going to guess (hope) mechanically it checks out, yes?

BTW, how did the plugs look? Were they or some of them wet with fuel? Or, were they dry? Any of them look "steam cleaned" as compared to the rest? Water (as in water in the fuel)? Coolant? (probably not if the compression check went well).

I'd want to pull the connectors off the back of the ECM one at a time and do a mechanical/visual inspection, just to be sure all the pins and sockets are clean and not out of position before reconnecting them. And same goes for the throttle position sensor connection (driver's side of the throttle body) and the IAC motor (opposite side). I'd like to eliminate any issues with the cam and crank sensor connections too. Might look at the O2 connectors too, while you're down there...again, just eliminating connection stuff as we go...

To complete the visual inspection, the plenum has to come off. Pulling the plenum is like a "right of passage" for LT5 drivers. It is a bit intimidating looking at it from the first time. But, after you've done it once, it boils down after all to just some screws and connectors and throttle cables. The biggest PIA is draining a few quarts of coolant and refilling after putting it all together. (And, THAT can be eliminated too, if plugs are installed in the injector housings that lead to the TB coolant lines! The plenum runs much cooler and pulling it for any reason becomes a 15 minute job after that!;))

So, a visual inspection of all six electrical connections; 4 on the plenum and 2 on the coil packs are in order. Nothing burnt or cruddy/corroded or wet? Plug wire connections and wires in good shape?

You may need new injectors, but I agree w/ you, far as the suddenness & severity of the symptoms go; the symptoms are too sudden and too severe to suggest injectors as the issue. Not to say you don't have an issue there, but just that the current circumstances suggest the bigger issue is elsewhere at the moment. So, it wouldn't be wrong to table the idea of replacing injectors just now - far as strict troubleshooting procedures go. However, if they are the OEM Multi-techs, I'd be wanting to replace them before reinstalling the plenum. (But, that's just me.)

With a couple alligator clip at each end of some (zip) wire leads, you can visually test the individual injector operation mechanical function and spray pattern.

Push in on the wire spring retainer loop and lift the plugs off of the injectors. Then attach one alligator clip to one of the spades on the injector. Turn the ignition switch to the on position to activate the fuel pump(s) momentarily. No fuel should be leaking on any of the injectors. Then with the other end of the wires connected to the +/- sides of the battery, you can tap the other alligator clip on the remaining injector post, listen for a clear "click-click as it opens and closes, and observe the spray patterns to check for uniformity.

Note: Even with new injectors I recommend doing this procedure to insure (1) none of the injectors are leaking, and (2) that they all work uniformly...ask me why.

Now we're looking at the coils. I'd want to compare the resistance across the plug wire posts of each coil and to ground. True, a VOM is not going to detect a high voltage (insulation breakdown) issue, but it will detect an anomaly if there is one - and there shouldn't be. Finding an anomaly is grounds for replacing the coil(s). If it is possible to test something, I never recommend replacing it for replacement sake. But, because proper testing is not within the capability (of my equipment), replacing them...may not be wrong at this point. Your choice.

Just for grins, are the injector housing bolts all at 20# of torque? If not, pull the bolts and put some blue Lock-Tite on them and re-torque them, starting from the center and working your way (in turn( out to the ends of the housings in simultaneous fashion.

Again, being you have the opportunity - plenum removed and all - now too would be a dandy time to verify the operation of the secondary system. (See Marc Haibeck's site for the procedure as to which wire to ground at the ECM connection to actuate the secondary vacuum solenoid switch.) (Or, depending on your emissions requirements, removing or tying the secondaries open could be done now, in conjunction with a chip configured sans secondaries - forever eliminating that system from becoming an issue at some point.)

One last thing to consider while the plenum is off is pulling the starter and inspecting the contacts and the copper ring on the solenoid that connects the battery with the starter armature. An emery board will go a long way to refurbishing the copper ring - removing pits and carbon and the like, as well as shining up the mating surfaces on the contact posts as well. A very light smear of grease on the moving parts would be a good thing too.

By now, if nothing has been discovered amiss, it may be time to reinstall the plenum and hook everything back up and see if the symptoms persist. If so, and without further indications of something not right - the scan isn't offering any clues, e.g., MAP sensor or the like, I wouldn't know what next to try but to borrow an ECM and compare. There's only one other electronic piece, the DIS, which is also under the plenum. But, if it was at issue there should be codes, and you have none indicating the DIS is bad (and according to gurus, they are rugged little bastards and seldom fail).

My sense of it is that something in this procedure should ferret out something useful, sans anymore help from the scanner.

Get back when you can. Maybe one of the Brothers nearby can lend you a hand. Sure would like to know what it is.

P.

[XfireZ51]

You say you are showing a lean condition and a secondary fault code? Vacuum leak somewhere? 7.5ms sounds like a LARGE PW for idle. But a lean condition may call for that and flood the motor. What do the plugs look like? R they wet? If you put a scan tool on it, just turn the ignition to ON and scan for the different nominal sensor values. Make sure each sensor is reading normal at 0 RPM ie MAP 97-100kPa depending on location, O2 .450v, CTS, MAT, etc. Check connections to ignition module. Did a critter gnaw on a wire?

[tomtom72]

:o Nobody said anything as to what a check of the fuel pressure regulator had to say? I would have checked that after I did the pressure test, KOEO by the book. The FSM protocol insures that both pumps are okay. The pressure was a bit down so the filter was swapped. PSI still down, so pump assembly was checked & cracked hose was found. This isn't consistent with loading up, no? Would not the motor be lean & smell lean?

:o Not trying to be a wise guy, but if it's loading up & shutting down from too much fuel....just saying the regulator bears a look, right. :o

If all of the above isn't the case then it's too lean, right? Nobody said anything about a lean smell from the exhaust. That is usually consistent with OEM injector failure as it's the coils that are the weak point on the 90's? The OE injectors rarely foul up bad enough to just dump fuel? I thought the design prevented that? Or do I have that wrong? Do we know for sure that the OEM injectors are still in the car? I can see my brand of injector thru the legs on the plenum.

Just my fwiw. Maybe two separate failures are at work here? I have a hard time matching the described symptoms to what was found to be physically wrong....or I'm stuck on the loading ( too rich ) up & shutting off symptom which makes me want to check the regulator & then move on to other things.
Please don't take me the wrong way! But something don't add up. :o

:cheers:
Tom

[Paul Workman]

You say you are showing a lean condition and a secondary fault code? Vacuum leak somewhere? 7.5ms sounds like a LARGE PW for idle. But a lean condition may call for that and flood the motor. What do the plugs look like? R they wet? If you put a scan tool on it, just turn the ignition to ON and scan for the different nominal sensor values. Make sure each sensor is reading normal at 0 RPM ie MAP 97-100kPa depending on location, O2 .450v, CTS, MAT, etc. Check connections to ignition module. Did a critter gnaw on a wire?

Hey Dom. Good you could check in. Hey, check me out: I considered that "lean" code too, but I put that aside b/c the ECM is in "open loop" until the engine warms up. I mentioned O2s and cross-counts, but as the OP said, it is a moot point if it won't idle more than 30 seconds.

At issue too, is the lack of codes or sensor readings, but a full set about now AND seeing the plugs would be more than a little helpful, huh?

And to TomTom... yer right about the regulator. :read2::sign13: If the diaphragm is cracked...who-boy! Talk about flooding! Again...MORE & MORE I wanna see dem plugs...especially the back 2 (where the regulator hose enters the plenum)!!

(I should be out working on my own car, but this problem has me intrigued!:icon_scra)

P.

[lbszr]

The OP mentioned spraying raw gas in the intake, it runs better. If this can be verified, possibly by a squirt or two to keep it running. This would rule out ignition, and internal engine problems and definitly be a lean condition to deal with. Although probably not the safest method if it decides to backfire at the same time.

Has the throttle position sensor and map sensor been checked for correct inputs to the ecm?

Mine had an intermittent O2 sensor causing mine to barely have enough power to move and die occassionly with no code. After about a month of this, it finally threw a code and told me which one. So I wouldn't rule out a bad sensor somewhere because of no code.

[XfireZ51]

It also sounds like it may be starting in "Limp Home" mode. What happens if you try feathering the throttle at start-up? It may not run long enough to set a code. With KEY ON, not start, does the CEL flash once or just come on?

[Paul Workman]

:o Nobody said anything as to what a check of the fuel pressure regulator had to say? I would have checked that after I did the pressure test, KOEO by the book. The FSM protocol insures that both pumps are okay. The pressure was a bit down so the filter was swapped. PSI still down, so pump assembly was checked & cracked hose was found. This isn't consistent with loading up, no? Would not the motor be lean & smell lean?

Revisiting your post (and others). Good points. But, I'm getting cornfoozing info here :confused:(could be just the way I'm interpreting it too, I suppose.)

I'd really like to see the list of "switch on" scanner codes, and then capture a set while it is running (of sorts).

In cases of "No codes", lots of fueling issues slip under the radar (it would be nice to have a FP readout on the dash or maybe the "A" pillar - I'm just sayin). But, fueling issues do not escape the plugs, and we've yet to hear/see how they look. (I'd believe plugs before what my nose would tell me at the exhaust pipe. Running with or without cats, or condition of the cats themselves makes a big difference in smell - to the point I have no confidence in MY snoot. Your snoot may be calibrated, and as such a valuable troubleshooting tool! ;))


Please don't take me the wrong way! But something don't add up. :o

:cheers:
Tom

I agree. I guess we're all waiting for more info...

P.

[sjs]

Revisiting your post (and others). Good points. But, I'm getting cornfoozing info here :confused:(could be just the way I'm interpreting it too, I suppose.)

I'd really like to see the list of "switch on" scanner codes, and then capture a set while it is running (of sorts).

In cases of "No codes", lots of fueling issues slip under the radar (it would be nice to have a FP readout on the dash or maybe the "A" pillar - I'm just sayin). But, fueling issues do not escape the plugs, and we've yet to hear/see how they look. (I'd believe plugs before what my nose would tell me at the exhaust pipe. Running with or without cats, or condition of the cats themselves makes a big difference in smell - to the point I have no confidence in MY snoot. Your snoot may be calibrated, and as such a valuable troubleshooting tool! ;))




I agree. I guess we're all waiting for more info...

P.




Thanks to all who have replied, lots of great info ... thanks especially to Paul as he read all the information in my posts and went even deeper.
I apologize for not getting back sooner, but some last minute stuff came up and I had to work most of the weekend. Also the car is in my garage not at my shop building so I don't have all my tools, hoping not to have to tow it!!!
Anyway, more info as requested with what I had time to learn. Fuel pressure regulator is fine ... changes with vacuum, holds pressure and vacuum and doesn't leak fuel internally or thru the vacuum port. Plugs truly are soaking wet, thats why it starts and runs okay after sitting for a couple hours, but after 15 seconds of operation time it loads up and NO throttle position keeps it happy. Won't restart unless in clear flood mode.
So .... Paul I agree completely .. I need to put the internal engine health question to bed with a compression test ... I thought crank vacuum and idle vacuum were low (althought hard to prove with a rough running engine) ... so tommorow I am going to pull of the plenum and compression test the old girl .... while the top is off I will resistance check the injectors and coils. I have an ignition DSO scope but it won't run long enough to accurately test it ... so upon everyones advice I think I will just replace the injectors and ignition while I am there ... if the motor is solid. If it isn't car just may have come up for sale as I don't have time this summer for a tear down - love the car just don't have time to play like I used too. If I did take the time to tear it apart - then it will get a full overhaul ... I don't like to make repairs twice! I will let everyone know if the stuff on top fixed it or if it is getting the reluctant "for sale" sign. If anyone wants a small project let me know. Thanks again to everyone.