Misfire issue

[INF3RN0666]

Originally Posted by 534BC

If you haven't got anywhere yet. Please post the conditions when and how it misfires. So far I am getting that it gets worse when warm and they are hard misfires (define) and it causes a vibration.

Some pertinant info for diagnosing may be

load/tps, rpm , engine temp, anmbiant temp, speed, ect. and then exactly what happens and how often the misfire is.

For the record, the misfire was consistent and it got worse when warm. RPM below 1500 made the car shake. Above 2000, I couldn't feel a misfire but that doesn't mean it didn't happen. The misfire would fade in and out (no pattern). For example, I'd come to a stop and it will be there or it might not be. But if I'm stopped and there's no misfire, it might just start misfiring again. Engine temperature never reaches 100 (midpoint) because I realized that my thermostat is probably stuck open. Speed doesn't matter because at high speed, the RPM is high, or even when you're cruising, the RPM stays above 1500 RPM. BTW, RPM values are strictly speculation (there's no tach in this vehicle).

[slammedGP]

I can't recall the fuse number, but you said it was throwing a bunch of codes? On my Grand Prix, i believe it is fuse #21 that controls the MAF, IAC, IAT, TPS, O2 sensors, MAP sensor etc. Might also be something to check into.

The MAF can cause a miss, and i've seen it on a couple occasions where a shop replaces the MAF more than once before the problem is fixed. In the shop i work at, they tried an aftermarket MAF from a generic parts store, with no luck, then they tried a rebuilt MAF also with no luck. When they finally tried a stock replacement from the manufacturer it was fine.

Do you have a cone or aftermarket filter? In some cases oil from the filter messes with the MAF. Have you checked for an air leak before the throttle body? That could cause the MAF code, and misfire. I have never seen a misfire back into the intake, at least not on a GM 3.8. There are a million things that can cause a misfire, and they can be easy to diagnose, or difficult to diagnose.

I have a miss in my 98 Grand Prix GTP. I've tried everything, with no fix. The only thing it can be for me at this point is a sticky or burnt valve. I bought a new engine anyway

[flyer728]

I'm having the same problem,,and it looks like a stuck lifter,,but the problem is when I change the lifter the new one will get stuck in the same place as the old one,if I swap to another place it will work fine....Go figure...still can't solve the problem yet...