94 ZR1 Intermittent Power Issues

[Reynolds Rides]

My 94 ZR-1 has started to have some power issues. Ill be driving (doesnt matter if Im in FULL power mode or not) and push on the gas and she will stutter and stumble intermittently. The power seems to kick in and out, and when the power goes out, it kind of pulsates the car. This happens on the highway and during city driving. The car isnt overheating but the weather has been hot and it seems to happen when she gets up to operating temperature. She runs great when cold and I initially start driving. No SES light on. Any thoughts or recommended starting points? Im leaning towards an electrical/ignition issue. She has 123000 miles and I dont really have any service history from the previous owner (just bought the car). TIA!

[1991 Corvette ZR-1]

Hi Reynold, like the videos. It could be a few things, but I went through something similar a few years ago similar where the car ran fine cold and once up to temp, ran rough. My issue was a bad primary fuel injector that wouldn?t provide a resistance reading when hot. Have you noticed a knocking sound at idle once the roughness occurs? I had the knocking/excess flywheel chatter at idle after the injector was heat soaked.

It?s not something that will throw a code, so it could be worth looking into. Marc Haibeck offers an invaluable guide on how to back probe the injector connections in the ECU bulkhead connector without having to pull the plenum. This is how I found my bad primary injector.

http://www.zr1specialist.com/HAT%20W...in%20Place.pdf

[Ccmano]

Fuel pumps could be an issue as well. Use this method to check the pumps....
http://www.zr1.net/forum/showthread.php?p=136108
H

[Reynolds Rides]

If the issue is fuel related, why wouldnt the car run rough when it is cold as well? Genuinely curious and trying to learn.

[Karl]

Originally Posted by Reynolds Rides

If the issue is fuel related, why wouldnt the car run rough when it is cold as well? Genuinely curious and trying to learn.

The car has two fuel pumps (primary and secondary). Both operate when cold and only one continues to operate when warm.

[1991 Corvette ZR-1]

Originally Posted by Reynolds Rides

If the issue is fuel related, why wouldnt the car run rough when it is cold as well? Genuinely curious and trying to learn.

More knowledgeable posters will chime in but here?s a brief post on it. Fuel injectors have a coil winding inside that is part of an assembly that uses electromagnetism to open and close off the passage way of a fuel injector. Opening allows the spray of fuel and the amount of time it is open is referred to as pulse width. When the coil winding becomes damaged from age and use, the pulse width instruction from the ECU can be compromised. It is amplified by heat, which soaks the entire injector coil winding and increases electrical resistance. The car may have a barely noticeable or unnoticed performance issue when cold because the injector(s) have not been heat soaked.

[Reynolds Rides]

Problem solved. I had an issue with the #8 spark plug not threading in all the way and it turns out that this was causing the car to run poorly. The lower threads were corroded so I chased them and now the spark plug goes in all the way and the car runs great. Thanks for your help. I made a YouTube video on the process. Check it out if you are interested:

https://youtu.be/RWaERjskaBk

[mlipmd]

Glad you found the issue and fixed it so relatively easy. Sometimes the problem is staring you right in the face and you just have to be smart enough to recognize it. And great video BTW.

[WARP TEN]

Originally Posted by Reynolds Rides

Problem solved. I had an issue with the #8 spark plug not threading in all the way and it turns out that this was causing the car to run poorly. The lower threads were corroded so I chased them and now the spark plug goes in all the way and the car runs great. Thanks for your help. I made a YouTube video on the process. Check it out if you are interested:

https://youtu.be/RWaERjskaBk

Glad you fixed it and thanks for the excellent video on the subject. Also glad to hear Marc Haibeck helped you out. He is a great resource--and good friend. It looked like the seat of the plug hole has developed a lot of crap on it since the old plug had been sitting high and probably a bit off of it. Were you able to clean that to get a good seal? And I presume you torqued the plugs properly and used anti seize on them? I always torqued everything but #8 and just estimated on that since it was hard to get the torque wrench on it. Never had a problem.--Bob