I know there are many posts about misfire issues in this forum, and I have read most of them. I've had this problem for about 2 years now, since I don't drive the car very much. Under load, the engine misfires badly above ~3000-3500 RPM. This happens every time and in every gear I've tested (1-3, 4-5 would be too fast). The misfire is so severe that the car has almost no power until it shifts. Low RPM's are pretty good with little to no hesitation. I'm guessing it's the opti, but the current one is rather new with less than 5k on it. The plugs are pretty new and the wires are very new. The wires are matched correctly on the opti and pushed on all the way. If anybody has had this problem, please chime in.

I'm thinking of selling the car... but will not sell unless this problem is fixed. All help is appreciated.

Thanks!

Steve

 

Could be your knock sensor pulling timing if it's bad. It could also be crossed plug wires.

 

Thanks for the suggestion. I've decided to take it to a shop (again)

EDIT: If they can diagnose the problem and the misfire goes away, I will post the solution. Many of the posts I read while researching highlight the problem with a few possible fixes thrown around but don't give final resolution

 

If you can, get ahold of a laptop computer an ALDL cable and download datamaster. then you acn get datalogs and see exactly what is happening when the problem occurs.

 

Always a good idea. I have a scanmaster which helps a lot as well.

 

Alright. I took it to a very good shop in town and had them diagnose the problem. They found that some of the spark plugs (which have about 8k on them) had fouled up causing the spark to shoot back into the spark plug instead of into the cylinder. The plugs went bad because the motor had not been running hot enough due to the 160 thermostat & electric water pump. So, now I've got new plugs in it and I also put in a 192 thermostat. The car runs like a BEAST now, and I'm glad to have it running like it should be.

I've never heard of someone having this problem, and I'm pretty sure that most people who have modified their LT1 drop in a 160 thermostat. I guess it's something to watch out for...