Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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?

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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:

Re: 91 ZR-1 Cutting Out Under Load
 

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?

Re: 91 ZR-1 Cutting Out Under Load
 

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%20W...Resistance.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.

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

http://www.zr1specialist.com/HAT%20W...%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.

Re: 91 ZR-1 Cutting Out Under Load
 

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?

Re: 91 ZR-1 Cutting Out Under Load
 

RC is Russ Collins

www.rceng.com

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

http://cgi.ebay.com/ebaymotors/Accel...QQcmdZViewItem
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%.

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

Yes.

Lots of info.

http://forums.corvetteforum.com/sear...archid=3367392

http://forums.corvetteforum.com/show...ight=injectors

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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

Pete

Re: 91 ZR-1 Cutting Out Under Load
 

Ouch $350. Any other options ?

Re: 91 ZR-1 Cutting Out Under Load
 

Your dealer is lazy.

17112220


Ray Denison Chevrolet
1-800-527-5452

Re: 91 ZR-1 Cutting Out Under Load
 

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

Pete

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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

Also, where is the ignition module located?

Re: 91 ZR-1 Cutting Out Under Load
 

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 ?

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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 ?

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

Coils.


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

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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

Re: 91 ZR-1 Cutting Out Under Load
 

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.

Re: 91 ZR-1 Cutting Out Under Load
 

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