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GTP random misfire/hesitation

machinegunsquid

machinegunsquid

New member
Ok, I'm new to GPF so don't bash me too hard.
I've got a 2002GTP with minor mods (3"DP no cat., MSD coils, MSD 8.5mm wires, and AC Delco Irridium plugs, along with a CAI) Recently I had a bad misfire under heavy acceleration, around 3-4k RPM. It would only miss a few times, then accelerate like normal, so I went and replaced the plugs (which had marks on the outside porcelain) with Autolite 104's. The car wouldnt Idle at all, and didnt want to run. So i put the old plugs back in, and it ran Perfectly, no misfire at all or anything.

Then later that day, I went to pass a truck (50-75) and i got a horrible hesitation/misfire. The car bogged horribly, and felt like it was starved for fuel.

Replaced the fuel filter, and checked the pressure at the rail, 50psi.
Checked vacuum, pulling about 20psi.

Any idea what it could be??
 


I've read a lot about MSD coils and people not really liking them. Do you still have the stock coils, they put our more voltage than the MSDs. Everything hooked up, Check Engine light?
 
Yeah, i still have the stock coils, but the weird thing is, now its just stuttering really bad under about 90% load, or more. But no misfire, and no SES light.
 
Time to res. this thread.
To anyone who's read through this looking for a cure,

what mine turned out to be was a split coil pack. I dont have any pictures, but the coil pack had a huge split between the contacts.

So if anyone is reading this thread to diagnose your car, wait until its dark, start your car, and while revving it, check for any sparks. =]
 


Sounds like the same problem i had with my MSD coils. Id punch it and it would hesitate for a moment. I switched back to my stockers and that problem went away. I like the way the msd coils look but they are a demod imo.
 
I have a 2002 pontiac Grand Prix GPT about 64000 miles on it and about every time you get on it it starts to miss the 1ST time replaced a coil pack and it seemed to be fine the 2ND time i replaced plugs and wires and it seemed to be fine again the 3RD time i replaced the same coil pack witch is the middle pack that is cylinder 3 - 6 but this time It still missing also it has been hooked up to a tester and it has a code of p303 or po303 need to find out what is the real problem???? Could it be a plugged injector ??? The car also has no catalac converter
 
its from not having a cat, had the same problem when I installed my headers and got rid of the cat and started getting the random misfires. The first thing I did was change the spark plugs but it didnt help what so ever. I installed a high flow cat and random misfires stopped =]
 
my car has the same prob right now..
I installed the headers & when i put some load on it will start to misfire :(
i cracked the little tube on the evap purge can. & i thought it would part of that if not completly the reason for the misfires & REALLY REALLY SUCKY MPG :( i replaced the evap can. & it help a little, mpg wise.. but for the misfires, well theyre still there :( i checked if we put the wires incorrectly but nop theyre in the correct place..
kinda sucks cuz i was really happy once the headers were on but now this..

I ALSO HAVE THE "SERVICE ENGINE SOON" ON... i still have a cat & the o2 sensors, i just extended the wire so it would reach & it did but after like a day or so of use of the car since its my DD, the SES turned on :/
 
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i had the same thing and i just changed spark plug wires and plugs. i went threw so much before it i did injectors ICM changed my coil packs. but then it was just plugs and wires.
 
I tossed on the ZZP coil packs and wires didn't have the problem for quite some time but now all of a sudden it feels like its misfiring but according to my scan gauges everything is normal? Any ideas?
 
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