robd98z28

Put a ’00 used LS1 motor with headers in about 1 ½ yrs ago and it ran great until about 4 months ago. First thing I noticed that as I pulled up to a light, it would act like it wanted to die, but would quickly recover. This randomly happened two more times, and on the third occurrence, the car would not start. Would crank and turnover, but would not fire. Took it to a mechanic who changed the crank and cam shaft sensors, this did not work. Same issue. He then looked at the electrical and determined it was a bad ground wire in the harness on the passenger side leading to the coil packs, so he cut into the wiring harness and ground the coil packs to the body. Car started fine and ran good, except, on the way home I noticed at redline RPM’s it was just very slightly missing. Continued to drive it for a couple months and it got worse. Car had a hard time starting and it was somewhat random, would run ok and other times would run horrible. Finally, it was just hard idling and wouldn’t get up to high RPM’s at all. Had to tow it to the dealer and they diagnosed it as misfiring mildly at Cyl # 6 & 8 at idle (warm), and badly at Cyl #2 at higher RPM’s. I think it also had an O2 sensor reading. They want to run a compression test to determine if there are mechanical problems with the engine, but I’m not convinced it is a mechanical engine issue.

Any suggestions? I've read other posts about O2 sensors, but none with specifics like this with Cyl 2, 6 & 8.

askkmb

iTrader: (3)

First i would replace the bad o2 sensor then i would check for spark. That could be the coils, wires or plugs or bad harness. if there is no problem then it could be the injectors. I think there could be more possibilities but this is what comes to my mind. Also, did you get it tuned after the headers? A customer last week removed the cats on a 02 Avalanche and also had a misfire. I logged it and the fuel trims were way off. Tuned it and it worked fine.