Pontiac Repair: 99 Firebird running bad, ac delco, lean mixture

Question
QUESTION: I've got a 99 Firebird V6 with 102k miles on it. The problem I am having is under load/wot it will sputter or sound almost like it's backfiring. it won't do it while idle or sitting still, only when in drive from a stop or while rolling. sometimes it runs great but most times it acts this way. I have replaced the ICM, Coils, Wires and Plugs all about 1500 miles ago because the ICM went up. it ran great till about 20 miles ago.

ANSWER: Hi Dave:
I would take a look at the coils on this. they have a tendency to carbon track meaning the spark jumps from the coil to the engine round rather then fire the spark plugs. you can get a spray bottle of water and spray down the plug wires and run the engine and then rev the engine up to load it up and I bet you will see either the coil or plug wire that is misfiring. The water makes for a more attarctive ground path for the spark to jump to goound thus cauing the misfire. For some reason that engine goes though plug wires. if you find the wires are bad get a good set of AC Delco wires or a good premuim set from NAPA or Carquest.

---------- FOLLOW-UP ----------

QUESTION: when I replaced the ICM I replaced the coils with ones from Summit, MSD wires and AC Delco plugs. It's not throwing a CEL either. Before I replaced everything it was throwing a p0306.

Answer
well if it's dropping #6 cylinder is could alos be the companion cylinder on that coil so it narrows it down by 1/3 where the issue could be. I have seenthese have fuel injector issue as well being that it's the last one in the rail a bad load of fuel run into the fuel rail would collect in one of the rearward cylinders. Not to common but it is possible. The fact that it pops and backfires would lead me to think it's still and ignition issue but an extremly lean mixture couls cause it as well but not as likley as a plug/coil or wire issue. What you put into this could be part of the issu as well. I don't care what brand name is on an aftermarket parts it's still that Aftermarket and it doesn't meet the standards set at the factory and with an ICM the base timing could be different then a stock module... good luck :)