Thread: misfire problem

well heres the deal about a week ago my cars ses light started flash and my engine stumbled whenever I would step on it. I have a scanning tool and ive been waiting for the chance to plug it in whenever the light came on. yesterday the light flashed and then stayed on so I scanned it and came up with a misfire in cylinder 4. Now i put all new plugs and wires about 25k ago but I inspected the plug and wire and they looked fine. I replaced all three coilpacks cleared the code pull out of my neighborhood twice and nailed it(Just to test it I dont usually drive fast) and the cars ran and idled the best it has since I bought it over three years and over 75k ago(car has 126k now) went out with my lady and drove all night winding it up every now and again just to test it and the car was just fine. I go out this mornin to run some errands. I was on the highway went to pass somebody and once again the car stumbled and the ses light flashed. Im thinkin ignition module but not sure. any tips would be appreciated. its a 04 gt 3.8na

What kind of plugs?

And before you go out and spend big bucks on a ICM, replace all the plugs and gap them properly to see if that solves your problem.

just fixed this yesterday on my car. same thing happened but it was cyl 3 right after laying into it light came flashing on and it had a misfire. so i brought it home changed the plug wire that didn't fix it so i swapped out the plug from cyl 6 and it still missed. then i checked it for spark there was no spark. so luckily i had extra coil packs laying around and i replaced just one of the coil packs and it worked fine ran nicely. still had the P0303 light one but i erased it and it didn't come back. it stayed on because it takes a few start ups for it to go off but its running good no with no problems. i have a 97 GTP

I used ngk tr55 platinum plugs. a bad plug doesnt make sense to me because if that was the case the car wouldnt have ran perfect for the whole night after I changed the coil packs and cleared the code. Ive used platinum plugs on all my gm cars and never had one crack before.

Waste spark eats platinums.

As said above, iridiums or coppers.

Actually, I read it once where Bosch wrote that their plugs in general do not do well in GM waste spark vehicles. Waste spark is when you have one coil fire two plugs at the same time. Our 3.8L motors do this. They fire 1 and 4 at the same time, which doubles the amount of firing a plug does because 1 and 4 aren't sync'd with compressed fuel charges at the same time. Therefore as 1 is evacuating exhaust, it's plug fires for 4 to ignite a charge and vice versa.

ok ill switch back to iridiums and see. but as i said in my first post i checked the plug and it looked fine. Im goin to check it again and see.