Need Diagnostic Help...2008 Grand Prix GXP

SleeperLS

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I am typing this out for a friend of mine. He has been experiencing these issues in his stock 2008 Pontiac Grand Prix GXP with 65,000 miles for several months now and it seems to be getting more consistent. I had him write out a synopsis of what is going on so this is a direct quote from him. Let me know what you guys think and if you need more info. I appreciate any and all help!

" My car intermittently stalls when I take off from a stop. It gives me a little gas and then just cuts out on me then back in and back out. When it cuts back in it shifts really hard. It feels as if it is running through the gears with pauses in between before it gets to 4th, then takes off. Then as I am driving down the road, my gauges will go crazy sweeping forward and back, but they do not actually reflect what the car is doing. When the gauges go nuts, they all jump at the same time and the car cruises normal at this time."

It sounds like it could be one issue causing all of these symptoms. PCM/BCM? I was thinking about changing his fuel filter, but it wouldn't explain his gauge issues. He says that when it gets going, it drives fine. Anyways, let me know what you guys think. He loves the car and it is driving him nuts.

I should probably tag the wizard himself... [MENTION=53]Turbocharged400sbc[/MENTION]
 

lastls1

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I know this generation of Grand Prix had a lot of problems with the BCM in the car intermit shorting, causing crazy things to happen with the dash, displays etc. I would start by checking that out.
 

RICH17

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I'd go through and find as many grounds as you can and make sure you clean them as well
 

SleeperLS

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I know this generation of Grand Prix had a lot of problems with the BCM in the car intermit shorting, causing crazy things to happen with the dash, displays etc. I would start by checking that out.
BCM located under the drivers dash or passenger dash?
 

lastls1

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Driver side if I can remember correctly
 

SleeperLS

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Thanks dude!

I do feel like all of these issue relate to one thing. It seems weird that multiple things would go wrong at the same time causing strange shit to happen.
 

lastls1

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No Problem. Alldata says below the left side of the instrument panel, left of the steering column.

And yea computers and wiring can make things go crazy. My GTO had the crazy gauge thing going on. It was a few loose wires behind the cluster.
 

boostedguy05

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The GXP's were hit or miss if you had a good one or not. they were either amazing cars with no isues, or you had every issue known to man happen. [MENTION=98]smug[/MENTION] i believe had a bad one.
 

SaturdaysGS

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Check the ground that attaches to the trans bell housing, open the hood and look down.. its by the right fan. Assuming that ground is the same as an 04 GTP. Mine was loose and it would act all sorts of goofy, pretty close to what he's experiencing.
 

SleeperLS

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I had him take a close look at all of the wiring especially around the engine and he found something interesting. Evidently he saw some mouse poop so he pulled off the engine cover and his MAP sensor wires are chewed up and somewhat charred. The connector and sensor look good, but the wires are definitely messed up. He is going to the auto store to get a bunch of stuff to replace the wires.

Bad MAP causing the surging issue? The dash issue I am still unsure of. He said the wires under the dash all look brand new and good.
 

EmersonHart13

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Any bad sensor or misfunctioning sensor could cause all sorts of issues in modern cars.
 

rocco

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Sounds like 2 different problems. The stalling/surging sounds like a MAF problem.

The instrument gauges sound like a bad ground or possibly BCM like you mentioned.
 

SleeperLS

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Any codes?
He said that there were a few codes that have not triggered the check engine light recently. When he took it to auto zone to see what codes were thrown, they were related to a wheel sensor and nothing engine sensor related.
 

SleeperLS

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Sounds like 2 different problems. The stalling/surging sounds like a MAF problem.

The instrument gauges sound like a bad ground or possibly BCM like you mentioned.
I was initially thinking MAF as well, but after seeing how chewed up the MAP wires were I am thinking that might be the issue. Would a faulty MAP signal cause similar symptoms?
 

SleeperLS

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Good to know. He should be fixing it today and getting back to me to see if the car works now. Hopefully it does. Thank you guys again for the input.
 

boostedguy05

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HOW THE HELL DID MOOSE POOP GET ALL THE WAY UP THERE :bowrofl:
 

SleeperLS

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So evidently he said it will still stall every now and again but it is drastically improved. I am going over there on Monday to correctly connect the wires and solder them together. He just has them somewhat crimped at this time and I am hoping getting a good connection will do the trick. I am going to do a really good inspection while I am over there and check stuff out as well. Is there a re-learn or anything I need to do that will help? Evidently he has been dealing with this issue for a year, so will his stock tune be learned all weird causing the issue still? I am also going to clean the MAF and inspect it on top of looking everything else over. Thanks again for the help guys!
 

EmersonHart13

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Just unplug the battery while you fix it, which should be done anyway...
 

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