On my way home today my truck started misfiring bad. Its a struggle to get up to 55 thats for sure. I have noticed it runs perfectly fine until it gets up to temp then thats when it starts. Temp and oil pressure are normal. Truck has new plugs and wires. Its just throwing a random misfire code so i cant determine where its coming from. Once it gets up to temp the service engine soon light is constantly flashing its like a constant misfire that dont go away. I even put my stock PCM back in to make sure the black bear tune wasnt any issue and i had the same results. I need to get this up and running asap and i'm out of ideas to try. Doesnt seem like it would be a fuel issue since it doesnt do it all the time and cant be a coil since its a random misfire. Its a 2001 with the 5.3. What to check now, what to try? Any input would be greatly appriciated.

 

It actually could be the coil pack, or maybe a wire. Also maybe a o2 sensor or bad cat. I've seen em do some crazy things

 

I dont have cats cause I have them long tube headers. I have been having that o2 sensor prb but we dont know if its cause if the tune or the actual sensor. Justins sending me out another tune to verify.

 

What plugs and plug wires did you use? Where did they come from? I agree that you can not completely rule out a bad coil pack just yet. Do you have problems get up to 55 mph under medium to hard acceleration? How about under light acceleration? Could very possibly be a fuel issue.

 

Ac delco wires and iridium ac plugs. It runs just fine until truck reaches temp then anytime your on the throttle its missin bad everyonce in a while when its around 55-60 its like its back to normal but just for a sec then its right back to the misfiring.

The part that gets me is how it runs just fine until it reaches temp.

 

Just realized it doesnt just do it when its warm just appeared that way yesterday from stoppin to try things then driving it again. It runs fine for about half mile to a mile then thats when it starts doin it.

 

You say you just installed new plugs and plug wires.....then the problem begins......hummmm.

I would look there.

Wires not "clicked" on.

Over tightened and cracked plug.Gap wrong...gotta use the correct type tool.

Header burns................etc.etc

 

Yes, check for cracked plugs and definitely headers burns. I had to do some modifying when it came to that cause I'd have burned 2 wires if I hadn't seen em. And did you change the plugs while doin the headers? Because I cracked 2 plugs(one on each side) when installing the headers. It must of hit the back ones just right

 

Got it all fixed, It ended up being that both o2 sensors went bad at once. Replaced them and the truck runs great and no more service engine light or any signs of a miss.