Electrical issue?

Tiny
JDEGIROLAMO
  • MEMBER
  • 2000 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 180,000 MILES
I have a 2000 WJ that ran fine when I parked it. It sat for 6 months as I just took to using my XJ. When I went to use my WJ it refused to start unless I gave it lots of gas, and would idle extremely rough, stalling out if I didn't sit giving it gas for a period of time. Eventually it would stay idling without me having to constantly step on the pedal. Once I attempted to drive it, it's extremely sluggish and unable to get any speed going, almost like it's in limp mode. When I try to accelerate, the radio shuts off, the odometer blinks on and off, the ABS light comes on, among other lights, generally things just go haywire electrically. I noticed that the volt gauge reads 9v all the time, even with the key on, engine off. I put a new battery in and checked the connections, the multimeter reads 12.6. When fiddling around on the engine while it was idling, I unplugged the field wires to the alternator, and noticed it started idling perfectly. Plugged them back in and it started idling really rough. Unplugged them again and it drove fine around town on just the battery. So, I took the alternator out and brought it to an Advanced Auto to have them test it. They said the alternator kept blowing the fuse on their machine. I bought a new alternator and slapped that on there. The same issue persists. Volt gauge still reads 9 even with the engine off, which I thought would just show battery voltage at that point. Any insight would be greatly appreciated.
Monday, May 13th, 2024 AT 12:54 PM

6 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,692 POSTS
I have seen the instrument cluster cause this issue, it has a short in the circuit board but to be sure let's unplug the cluster and start the engine to see if there is any change, here is how the job is done. Check out the images (below). Please upload pictures or videos in your response to any problems so we can see what to help you with.
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Tuesday, May 14th, 2024 AT 11:42 AM
Tiny
JDEGIROLAMO
  • MEMBER
  • 4 POSTS
I unplugged the cluster and the issue persists.
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Monday, May 20th, 2024 AT 12:25 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,692 POSTS
Okay, so when the engine is running good without the alternator plugged in correct? Can I ask if the alternator is charging? this guide can help you.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

If the alternator is not charging I would check the fuses which are mentioned in the alternator wiring diagrams below. If they are okay it sounds like the PCM is bad. You can remove it and send it into a rebuilder for testing.
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Monday, May 20th, 2024 AT 12:39 PM
Tiny
JDEGIROLAMO
  • MEMBER
  • 4 POSTS
Engine runs fun with the field wires unplugged. Plugged in it gets really rough. Took a multimeter reading with alternator plugged in and it was reading upwards of 17-17 volts. As soon as I unplug the alternator again the jeep stalls out. Did an ohms test on the fuses and had zero resistance, plus they looked ok visually.
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Tuesday, May 21st, 2024 AT 6:25 PM
Tiny
JDEGIROLAMO
  • MEMBER
  • 4 POSTS
Unsure if this is out of spec or normal but I did an ohms test on the ground field wire to the pin on black pcm connector and had zero resistance. With the connector plugged in I did an ohms test on the ground field wire to the negative battery post and get.350

Appreciate you're help. Thinking im gonna need to send the PCM in to get repaired. What are your thoughts on possibly trying an external voltage regulator, if that's even the issue.
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Tuesday, May 21st, 2024 AT 6:30 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,692 POSTS
17 volts is too high, so you have found the problem. I would swap out the PCM which controls the alternator. Please let me know how it goes.
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Wednesday, May 22nd, 2024 AT 10:47 AM

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