3800 S/C Stutters

[024Man]

Have a 99 3800 Stage II Supercharged Grand Prix. Lately I have been getting some stumbles and stutters on acceleration. I took a scan and found the scan attached, as well as P0300 and P0306 DTCs. The RPM sharply drops off while throttle position and the MAP/MAF indicate constant running. Changed the plugs, wires, and swapped coil packs to no avail. Fuel pressure is good. Even ran Seafoam thru a tank of fuel. I am starting to think it could be an injector, does not seem possible two coil packs are bad. Any idea where I should start with regard to troubleshooting further.

Attachment 31459

[GeoJB]

If you figure this out let me know.
Every so often I'll get the same thing.
I just live with it.

[murphinator]

havent had that happen but seeing the injector duty cycle plunge like that while all the other vitals are steady state ( other than rpm which must be caused by the IDC drop) my knee jerk reaction is power to injector/injectors , bad plug ,loose wire , not clipped all the way in , bad ground , etc...

good job isolating the problem in a scan frame !!

[gn2beatu]

It is cylinder #6 that is misfiring. Since you swapped all the parts, swap the injector with another cylinder, and if the code changes to the cylinder you swapped to, its your injector. I would also do a compression test for sure on cylinder #6. Might want to do a leakdown test too, but 100% for sure do the compression. G/L

[Trent_Petersen]

If its a wiring issue with the injectors it should not show on the IDC in HPT, you are just seeing what the computer is commanding and not what is actually happening.

I had a car that was doing this pretty bad and it turned out to be a Ignition control module. There were no CEL's and the module tested good several times in a row on a bench tester here at work (Napa). But after I replaced the ICM all was fine.

The Drop in RPM's would cause the drop in IDC, because your injector pulse width is constant.

I would look over all the plugs with the crank and cam sensors and the ICM, if you have another ICM swap that out too and see what happens.

[xpzd3800]

try swapping out the ICM. under the coils. did this a while back and I had similar issues that cleared up.

[MMGT1]

Swaped packs with new units I take it? Did you test the coils to make sure they were good? Should be between 5-7K ohms, test em out to make sure they all are close and in range. That looks to be coil or ICM related to me like the guys are saying.

[REDNECKRACING]

i would check the spark plug boots. i kept having mine blow out on me on cyl 4 and cyl 6. i got heat selves on those 2 and have not burned one since. i think because it it throwing the misfire codes it is spark related.

[xpzd3800]

crank sensor?

[Mercedesrepair]

Try tightining the plug gap, dont run the stock .060 . try .040

[MMGT1]

If you're commanding 11.2 in PE, there must be some crazy boost going on there. If your boost is high enough to warrant that AFR, then yea, gap those plugs to 40! That drop is making me think that xpzd is onto something there...