Ok, I will try to give everyonr enough info so that I can get some opinions. 99 Z28. NGK TR55s magnecor wires, premium gas, hooker longtubes. After starting the car it will run good for 5 minutes then it will start misfireing for another 5 minutes usually in drive on the move but not always. I started by unprograming engine performance hypertech PP, which helped for alittle while but began doing the same thing later on that day. Then I changed the spark plugs which seemed to fix it, it was running like a champ for a whole day then began the same thing. Could It be some bad gas? I used some HEET its a water remover and injection cleaner, nether helped. Could the wires be burnt up from the heat off the headers? the wires are about 25,000 miles old. mabey a coil out. If anyone has had this happen or any opinion would help alot. thanks.

 

most likely a heat issue.. something could have been damaged or fatiuged(sp) in some way..

wire might not be on all the way and with vibration allows the spark to make a jump to the plug..

when does it missfire? at idle? cruise? part throttle accell? Wide open throttle?

 

usually crusing or part throttle, I noticed if push down the pedal to about 3/4 throttle or more it will push out of the misfire, it just dosen't make any since. why does it only happen some of the time, its very frusterating. Could it be something in the computer? When it first started the SES light came on and it flashed while it was missfiresing, but after I changed the spark plugs and reset the computer it hasen't come back on. ask more questions if you need..

 

Check your plug wires, if they're all fine it could be a bad coil pack.

 

That kind of what I was thinking but I have never heard of anyone with that problem before. The car has around 62,000 miles. how do you test the coils to see witch one is bad?