92vettelt1

Okay. I have a 92 corvette LT1, it is one of the earlier LT1's made so I do not know what all is different because I know they made improvements along the way through 92 to 93. The problem started about a year and a half ago, the car would run good when it wanted to, and missfire bad all of a sudden. You would get in the car and it would be like flipping a coin. It progressively got worse and started to missfire all the time. I figured to do plugs and plug wires first because the engine is known for having crossfire. Bought a cheap set of autozone plug wires just to see if it would fix the problem... I also found that one of the terminals on the opti had corrosion on it, so i used some pb blaster to help loosen up the corrosion and a wire brush to clean it up. THis made it tremendously worse, the car was missfiring but also was backfiring and spuddering under load... Checked the wires for resistance and quite a few of them were 10k+ ohms. Replaced with a set of 8.5mm summit street/strip wires and bought wire looms for the wires. This got rid of the backfire, but it still misses and spudders under load.

THe car is completely stock and it keeps throwing me through loops trying to figure out what is wrong with it. Also when the problem started, with the car running in the driveway NO garage door opener would work. As soon as you shut the car off... they would all work fine. Not sure if this helps but I am starting to lean possibly toward the ecm for this reason only.

All help would be greatly appreciated, thank you.

mrmint69

How many miles? If the opti is origional it might need replacing. Have you gotten any codes or had it scanned?

92vettelt1

car has 42k on it with original opti, i think we got code 16 out of it once a long time ago which was the opti, but it hasnt had any codes since then which was forever ago.

mrmint69

16 year old opti might be a problem but the miles are lower than almost everyone else. The harness might be the problem. There could be several things causing it so if you have any way to scan it that would be my advise. I personally would replace the entire opti and harness and eliminate that but its your call.

Colin

Have you ruled out fuel pressure? I know, it sounds stupid but you have to check the basics. Also, are you using dielectric grease on all plug terminals? It helps prevent terminal corrosion. Have you checked your alternator when the car is stumbling? An easy test is to jump across the battery terminals to check voltage.

Other possible things could be EGR. If it is stuck open you typically get a code 32, I think, but the EGR was bad in my IROC and it never once threw a code. It would stumble intermittently like you are describing and sometimes would run great. An open EGR floods the intake tract with unburnable gases, hence the stumbling at idle and part throttle.

I'd do some more troubleshooting before you tear into your low-mileage C4. An opti isn't a cheap part to purchase and as aggravating as it may be to try and figure out what is going on with your car, throwing away $400-$500 and then find out the problem was not the opti but a $15 sensor wouldn't make your day. Just my $0.02.

Later,
Colin

Injuneer

Are you using resistor plugs and spiral-wound (not solid copper) plug wires? If not, you could experience high voltage RFI interference that can screw up the ECM (and maybe your garage door opener). RFI interference can also corrupt the pulse signals from the Opti, and the frequency signals from the knock sensor.

92vettelt1

did some testing today, alternator tested fine. i had a broken wire on the coolant temp sensor, thought maybe that would be causing the problem, fixed it and nothing changed. I also pulled a few spark plugs and the 2 i checked seemed to have week spark and didnt seem to affect idle quality(did both one at a time)... was wondering how to check resistance on the ignition coil to see if it is good or not. also if someone could tell me where the egr valve is to mess with that a little. For injuneer the plug wires i am using are the spiral-wound, and the plugs i am not sure if they are resistor plugs or not they are bosch platinums.
Thanks.

LaredoZ28

The EGR is on the back of the intake. behind the fuel pressure regulator.