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Unexplained DTC’s, engine will not stay running

Tiny
DANE DESPAW SR.
  • MEMBER
  • 2003 BUICK RENDEZVOUS
  • 3.4L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 240,000 MILES
I recently bought this car to flip and make a little cash on it. Replaced the heads (used but known to be good), intake manifold, head gasket set, EGR valve, MAF sensor, fuel pressure regulator, CKP, harmonic balancer, plugs, wires, and coil packs. Currently it runs but has a general misfire dtc. I’m also getting dtc’s for the MAF sensor. When I start it, it will idle for less than 5 minutes and then stop running. It always starts right back up when I turn the key. I’m starting to think that I might have to consider that the PCM may be going bad. Thoughts?
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Monday, July 4th, 2022 AT 12:27 PM

6 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,968 POSTS
Yep, it could be bad, I would clear the codes, then turn the key on without cranking the engine over and then run the codes again, this will give us the most prominent code to address first. Also, you can try to reboot the system by touching the negative battery cable to the positive terminal for 2 minutes, this will discharge the capacitators in the system and allow a reboot. Let me know what happens. Here is how to change out the PCM in case you need it. You can get a preprogrammed unit online. Check out the diagrams (below). Please let us know what happens.
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Tuesday, July 5th, 2022 AT 12:46 PM
Tiny
DANE DESPAW SR.
  • MEMBER
  • 72 POSTS
So, clearing the codes and rerunning the scan doesn’t produce anything. It simply says there are no dtc’s.
I need a little clarification on rebooting the PCM because I’ve never done that before. And it may seem like a stupid question. You advised me to touch the negative battery cable to the positive terminal. Am I supposed to disconnect the positive cable first?
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Thursday, July 7th, 2022 AT 12:25 PM
Tiny
DANE DESPAW SR.
  • MEMBER
  • 72 POSTS
Follow up question.
If I reboot the PCM will it need to reprogrammed?
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Thursday, July 7th, 2022 AT 5:04 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,968 POSTS
No, this procedure just erases the "learned memory" and lets the system start over. Let me know.
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Saturday, July 9th, 2022 AT 9:47 AM
Tiny
DANE DESPAW SR.
  • MEMBER
  • 72 POSTS
Rebooting the PCM didn’t do anything for me. Also, I noticed that in my initial question I failed to mention that the engine is actually misfiring with all the ignition components having been replaced. I hope that didn’t influence the advice you offered.
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Friday, July 15th, 2022 AT 5:42 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,968 POSTS
Yep, that changes things, lets remove the spark plugs and do a compression test, while the spark plugs are out see if there are any that are a different color. This guide can help, also if you want to upload a short video of the engine cranking over I can see if the engine is okay or not.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run down this guide and report back.
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Friday, July 15th, 2022 AT 10:42 AM

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