Can anybody figure this out

[liquidflesh]

Here's my delema. My normal grandprix forum hasn't been able to quite pin point this so here it is.

98 GTP 3.8 s/c
Normal driving, everything is fine.
Normal Acceleration, everything is fine.
Hard Acceleration when my boost gauge shows boost, the engine stumbles, if i keep on it then my ses light comes on and it is a P0303(#3 misfire) Same code every time. If i let off then the engine goes back to normal, no code, nothing.

I changed the following over the weekend, Plugs, plug wires, LIM gasket, S/C gasket, v/c gaskets, injector o-rings, fuel filter. I tested my injectors, and injector harness.

After all that it still stumbles under hard acceleration, and it is always in sync with my boost gauge. when it shows boost, engine stumbles.

Any idea's

[BNaylor]

Welcome to AF.

Well it looks like you ruled out a fuel supply issue. Most fixed cylinder misfire DTCs are ignition related. Since you replaced plug wires and spark plugs try swapping the coil packs around. 2/5 with 3/6. Also, get the ignition control module (ICM) tested.

When it stumbles around what rpm?

Also, post your mileage in these type posts and are there any engine mods or is this GTP stock?

[jessiebighamKC]

Yeah I would agree with the one above me! I would take the ICM(Ignition Control Module) off and have it tested. If there is an advanced auto around you can take it there or another parts store and they can test it! I had the same problem and it was my Ignition Coil Packs!

[liquidflesh]

will do guys, thanks. milage is 160k, there is not standard rpms, as it only happends when i punch iut hard, i could be going 70 or 10mph and it drives like a dream. it is only when i accelerate harder than normal and my boost kicks in that it stumbles. only mods i have are k&n, borla cat back system.

[liquidflesh]

i had the icm tested. it is good.

coil pack is good but in the low end of the tolerance.

new development. If i take the s/c belt off. My problem goes away 98% of the time......

[grandprixgtx00]

what kind of gas are you running in your GTP? seems kind of weird that when you take the S/C belt off it quits. weird for a #3 missfire...

[liquidflesh]

i always run premium. I swaped coils and the misfire moved to #5. so i installed a new coil and i am gonna take it out for a drive after dinner.

thanks guys

[liquidflesh]

everything fixed. it's funny cause i already swapped coils once before, and nothing came of it, but this time when i switched the misfire moved.

Thanks for your help guys