Grandpabill10

My '96 LT4 engine misfires during normal acceleration 'only' when the a/c is on. I have tried going through the gears with the a/c on and off and when the a/c is turned off there are no misfires. But when I turn
the a/c on, the engine misfires between 1500 and 2500 rpm in first two gears, but seems to fade away when getting up to speed. I do not
detect any engine misfire when driving highway speeds with a/c on.
Anyone know what is going on?

Thanks,
Bill

fatboywilly

Sounds like it could be time for plugs or wires. If plugs are weak they will misfire when put under a heavier load. I've had the same problem before. Maybe time for a tune-up.

Grandpabill10

Thanks for the info on plugs and wires, but I just changed plugs, but not the wires.
The car has 36,000 miles. Is it normal to have to change wires by mileage or do
you go by how old they are?

zr1fred

It could also be dirty/fouled fuel injectors, weak pressure regulator, or clogged fuel filter. Age is in many cases worse than mileage, especially on non rotating parts.

fatboywilly

Age baby. They break down. Even if we look good. We still poop out sometimes.

George Dickel

I had a 93 that would misfire under heavy acceleration, but would not misfire if I was driving it easy. Turned out to be a couple things, the PO had a shop install new plugs but they only did the drivers side not the passenger side. Even after I replaced ALL the plugs it still misfired but not as badly. The main culprit was the coil wire shorting out.

Grandpabill10

Thanks for all the help guys. I'll check everything you mentioned. Hate to think
of changing that plug wire on the back end of engine on passenger side. It's
a big headache getting to that plug.

Doggie Dawg

do you have an after market k&N air filter or any after market air cleaner?

Thats your problem

subavairpine

Well I have a '93 that had a similar issue, it would only misfire under load, but if I was easy on the accelerator, it was fine... replaced the opti and the problem is gone. Runs perfectly now. But that was my case... in reality, it could be any number of things - plugs, wires, injectors, fuel filter, icm, etc, etc... just have to troubleshoot it out or find someone who knows vettes.

btw I have a K&N air filter, and that doesn't/wouldn't cause any issues if it's clean...

Grandpabill10

Thanks subavairpine for the tips on troubleshooting my misfire problem. I had a leaky
waterpump for a short while and was hoping that had not caused problems with the optispark.

l98tpi

If it only hesitates or seems to mis fire with the a/c on then it is probably the a/c compressor beginning to go bad internally.

If the car hesitated all the time ac on or not then it could possibly be something else, but since the symptom only occurs with the ac on then it would point to ac issue.

Grandpabill10

Great news on my engine misfire when the a/c is on. Finally got the car into the Chevy dealer and went for a ride with his scanner attached. Found no engine misfire although the engine was jerking every so often between 1200 and 2,000 rpm. The mechanic then checked the a/c and found out that it was turning on and off every few seconds and also the turning off and on coordinated with the engine jerk. Went back to the dealership and found that there was only .5 lbs of refridgerant. Added the correct amount of refridgerant and went for a drive. The a/c stopped cycling off and on and the supposed engine misfire went away. Yippee!