91 alternator tests good but doesn't charge battery
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
Apples and oranges. Mud, I believe your (internally regulated), alternator output meets a wire to the battery on the starter relay there near the battery. (there is a diagram in my signature). Coach's (externally regulated) might meet in a PDC?.
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
jmrec100, Without really knowing I'm thinking that is not so easy. (it's a PCM Btw, ECU is 90 and earlier). It might be the PCM does not actually provide field current, but instead a signal to the (post 90) alternator, telling something internal how much field current to provide.
If your Alt and connections are now OK, maybe a replacement Powertrain Control Module might be your best bet. Might be relatively affordable at pick n' pull.
If your Alt and connections are now OK, maybe a replacement Powertrain Control Module might be your best bet. Might be relatively affordable at pick n' pull.
Thank you for that link. Someone had extended the wire for the fuse to rest behind the headlight (who does that) and the wire had shorted out. Replace the wire and the fuse and she's back!
CF Veteran
Joined: Aug 2011
Posts: 10,489
Likes: 24
From: Nor-Cal Coast
Year: 90,84
Model: Cherokee
Engine: 4.0,2.5
HEY! We got a Bingo!
. Well done, Happy trails! (I'm not aware of any fuse between my alt. and where it meets the wire from the battery at the starter relay)
. Well done, Happy trails! (I'm not aware of any fuse between my alt. and where it meets the wire from the battery at the starter relay)
Last edited by DFlintstone; May 17, 2014 at 12:06 AM.
Yeah I believe that's where my problem started. I've never heard of the fuse. The wiring looks like it was installed aftermarket. There are a couple things I'm still finding. (Aftermarket voltage Regulator bolted to fender)
Seasoned Member
Joined: Jun 2013
Posts: 380
Likes: 1
From: Southern California ( for now)
Year: 1994
Model: Cherokee
Engine: 4.0L, In Line 6
jmrec100, Without really knowing I'm thinking that is not so easy. (it's a PCM Btw, ECU is 90 and earlier). It might be the PCM does not actually provide field current, but instead a signal to the (post 90) alternator, telling something internal how much field current to provide.
If your Alt and connections are now OK, maybe a replacement Powertrain Control Module might be your best bet. Might be relatively affordable at pick n' pull.
If your Alt and connections are now OK, maybe a replacement Powertrain Control Module might be your best bet. Might be relatively affordable at pick n' pull.
PCM. Got it. It's the 'brains'. I did get a rebuilt PCM. Issues gone. But I sure as heck check my grounds every month or two.
I was asking about how to go external voltage regulator. But didn't think can. I'd rather fry alternator than the PCM again.
I was thinking of just buying another PCM. But would have to have all the same options as I have on mine. I went and had to drop an engine/trans in my beater DD Chevy Cavalier. Had a heck of a time getting the right computer for it. Eventually, ordered one and had it programmed for my specific model. A pain in the ..... Is it the same for Jeeps? I imagine it is.
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