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Occasionally surges and stalls

Bedwards

Bedwards

New member
Hey guys. I got a 1999 Pontiac Grand Prix GT with a top swap, VS cam, headers, intake etc. A few days ago, as I was accelerating from a stop, my RPM started bouncing between 200-1500, back and forth, nearly stalling it. If I let off the gas, it stalled. It fired right up, but it stalled 2 or 3 more times when trying to accelerate again. I also noticed the battery light illuminated on the dash. The car ran fine for around a day after that. Then it started up again. I assumed it was an alternator issue, so I replaced that. It was working great for a day or so, but today it happened again. The car surges and wants to stall. Any ideas? Maybe the charging wire coming from the alternator is intermittent? Thanks.
 


Sounds like nonfunctional maf to me. If you unplug the maf and there's no change, maf could be dirty, broken, or wiring bad. Could also be a big vacuum leak.

Any codes?
 
Hmmm. Okay. I'll look into the MAF. I also noticed the "Trac Off" light came on when after it stalled. It's been staying on ever since. Not sure why.
 
Tried a different MAF, and it still stalled. I unplugged the MAF and it was running okay for a bit, then stalled a few times. I cleared my DTC's since I had a bunch of old ones. I started my car up and immediately got a P1374 code. Any idea if this is causing my problem?
 


Oh yeah, no harm in checking the ICM first. I was running through stuff quick and read "DTC P1374 Crankshaft Position..." and closed the window.
 
In the steps listed on correcting the DTC, no mention of replacing a CPS is made. It talks about testing the ICM, and all the associated wiring in the system. Hmmm.
 
it says, [h=1]DTC P1374 Crankshaft Position (CKP) High to Low Resolution Frequency Correlation[/h]

Test for the following conditions:
•
A malfunctioning ignition coil--Remove the ignition coils and inspect the ignition control module and the coils for cracks, carbon tracking, or for other signs that indicate that the coil secondary circuit is arcing to the ICM or to the ICM wiring harness. Refer to Ignition Coil(s) Replacement .

•
The secondary ignition wires arcing to wiring harness--Inspect the secondary ignition wires for carbon tracking or for other signs of damage.
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

sounds like it thinks you have a bad wire maybe, or a problem from the icm to the crank sensor. id check all that out. got to better then changing the crank sensor.
 


I just noticed the rear bolt that mounts the coil bracket to the block is missing, which is the bolt where the ground to the ICM connects. The ground wire is floating loose in the air. How does the car even run with no ICM ground? This is probably what's causing the DTC hey?
 
The wire must have been close enough to the block to arc and cause it to stall. I also noticed when I hooked up my HP Tuners and took it for a scan, every single cell in every rpm range had a timing value of 10. I don't have access to getting a bolt tonight, but I moved the ground wire far from the block and it hasn't stalled on me since. Cross my fingers.
 
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I hooked up the ground and I am still getting the stalling and surging issue. I noticed the issue is worse when the car is cold. Here are all the codes that just popped up:

P0140 - Turbocharger Wastegate Solenoid 1
P0300 - Engine Misfire Detected
P0306 - Cylinder 6 Misfire Detected
P1381 - Misfire Detected - No Communication with Brake Control Module
P1374 - 3X Reference Circuit (came back)
P0730 - Incorrect Gear Ratio (I've had this one for a long time, long before this issue started)

I'm going crazy. Where do I even start?
 


Um. Pull spark plug 6, check for damage/foul. Check the injector wires, too. Swap coil 6 with another and see if the misfire migrates.
 
Plug looked okay. Wire looked fine. I cleared the codes and I'll see if that misfire comes back. If so, I'll swap the coil. I tried another PCM, didn't fix the problem.
 
After clearing the codes, I immediately got codes P0243 and P1374 on startup. Could a bad ICM harness be causing this? I'm at a stand still.
 
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