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Username Post: 2002 Pontiac Grand Prix GTP supercharged erratic sensor readings and stalli        (Topic#352445)
Posts: 197

Age: 29
Loc: Fargo ND
Reg: 01-25-16
08-11-18 07:35 PM - Post#2742781    

Hi everyone, im having some issues with my 2002 Grand Prix GTP, first had fuel starvation issues because the PO twice installed a GT fuel pump instead of the GTP pump, i installed the correct one and the stalling has been gone for several weeks. now ive been noticing hard starting mostly when cold, (more than 4 seconds before it pops off, or it dies right away then will start up next try. i get a few DTC's one was O2, bank 1 sensor 1 insuficcient switching, coil 1/4 high reference voltage and MAF low frequency. the obvious issues is reduced fuel economy (12-14mpg average even when staying out of boost) randomly while sitting, either in park or in gear the engine will start surging to around 2000RPM then back down to 300-400 or even stall out, then repeat. i have recorded videos of the sensors i was monitoring this evening, and you can see the voltage all over the place and sensors showing completely erratic input, even though im not doing anything. I checked with my dvm and im showing a rock steady 13.45V at all the PCM fuses, and the junction block. (i know it could be more but ill deal with that later) point being that my source voltage is steady.

Tomorrow im going to check all the grounds, try and get access to the PCM and probe voltage directly on the pins showing voltage fluctuation, otherwise im not sure what could be causing this other than a failing PCM.

Also does anyone have a pinout or a list of grounds for this particular year? i will be searching tonight but it never hurts to ask lol

1994 T15 Jimmy 4.3LCPI/4L60E 170K 3.42s (DD)
1988 V20 Suburban W/1995 454TBI(32PSI)/4L80E/NP241 CA truck, 125K G80 14SF/ GM10 4.10's
1995 K1500 ECSB 5.7 TBI/4L60E, 3.73s 269K(wifes)
1996 K3500 ECLB DRW 6.5L TD 3.73's 198K (new project)


Frequent Contributor
Posts: 1953

Loc: Lake George, NY
Reg: 11-11-15
08-12-18 10:49 AM - Post#2742838    
    In response to MuddiGGer25

Maf sensors were a common failure issue on that generation of GM cars, some of your symptoms could be attributed to that. Sometimes cleaning them works, not often though. Make sure no vacuum leaks.


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