91 ZR-1 Cutting Out Under Load

[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?

Originally Posted by GregCrowe

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. 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

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!


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!


Tom

[GregCrowe]

Originally Posted by 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!


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.


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.

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.

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.


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.