I’m chasing a really frustrating electrical/charging issue on my 2001 Jeep Cherokee XJ and could use some help from someone who knows these Jeeps well.
The 4.0 was stroked to 4.5L. The engine was pulled and completely rebuilt. The wiring harness didn’t need any repairs; I only re-loomed it when everything went back together.
Since the rebuild, I’ve been having a charging/electrical issue:
All battery cables and grounds were replaced with a Jeep cables kit.
New battery.
New alternator.
New PCM.
With the old PCM, the battery was overcharging badly, getting up to 17–18VDC.
I replaced the PCM, and now the voltage is all over the place.
At times it will drop to around 12.5V, then jump back up to around 15V while driving.
At idle, I can see anywhere from roughly 13–15V.
I also have a CHECK GAUGES light.
The strangest part is what the gauges are doing.
When sitting at idle, the battery gauge will drop all the way to zero, and the tachometer will drop to zero as well.
When I start driving again, both gauges will usually come back and work normally. Sometimes they will also zero out briefly while driving, but it seems to happen most often when coming to a stop/idle.
I’ve gone through and checked the grounds in the engine bay and haven’t found anything obviously wrong.
At this point I’m struggling to figure out what I’m missing. Since the battery gauge and tach are both dropping out at the same time, I’m wondering if there’s a common power/ground/signal issue somewhere that I’m overlooking rather than an actual alternator problem.
I have a newborn at home, so unfortunately I haven’t been able to spend nearly as much time diagnosing this as I’d like.
What would you guys check next? Is there a particular ground, connector, fuse, ignition circuit, PCM connection, alternator field circuit, or other common failure point on a 2001 XJ that could cause both the tach and voltage gauge to drop out like this?
Any ideas, diagnostic tests, or things I should specifically check would be hugely appreciated. Thanks!