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Alternator or what? HELP!

Samson04

NAXJA Forum User
Location
Taylorsville, KY
Okay, 98xj 4.0, AW4, 185K miles. Late last week, check gauges light comes on, charge gauge is buried all the way to the left. A little further down the road the belt starts to squeal. I pop the hood and shut off the engine. everything seems ok. I start it again and the charge gauge goes up and all is well. Next morning, same thing, so I figure that the alternator is going bad. after all, as far as I know, it's the factory unit. I take it to a guy that rebuilds them, he calls me this morning and tells me that, other than being full of mud, the alternator works fine. If it's not the alternator, what could it be? Any help greatly appreciated. Right now I'm borrowing a vehicle and need to get my xj back on the road ASAP! Thanks!
 
I'd take off the belt and spin all of your pullies. Ones that feel like they are grinding will have bad bearings. I have a feeling something is locking up every once in awhile, causing the belt to squeal and not spin as fast, which would lower the charging from the alt.
 
That's what I thought at first, and I will still double check, but when I popped the hood the first night everything was turning that is supposed to and still no voltage on the gauge. The gauge doesn't bounce or wiggle at all, it stays all the way to the left. Also, the belt doesn't squeal all the time, only every once in a while.
 
have you reinstalled the alternator after him cleaning it and checked to see if the light is still on? the mud could have just caused the contact between the rotor and the stator coils to be poor..the belt squilling could have been caused by the rotor not being able to turn causing the belt to slip over the alternator pully.So reinstall the alternator and see if it does it again
 
I'd take off the belt and spin all of your pullies. Ones that feel like they are grinding will have bad bearings. I have a feeling something is locking up every once in awhile, causing the belt to squeal and not spin as fast, which would lower the charging from the alt.

x2 on that if the alternator was installed after cleaning and the belt still slips
 
1. Inspect your belt. This could be a belt issue. If the belt is glazed, old, (more than 60k) replace it! Goodyear Gatorback is a good replacement belt. And know that the belt on the 4.0 needs to be pretty darn tight to work efficiently and keep quiet.

2. The voltage regulator is in play here. Especially when the voltage rails high on your voltage gauge.

The voltage regulator is inside of the computer.
 
Last week, my '96 started behaving in a similar fashion. Volt needle up and down, radio buzzing, whether on FM, CD, or Sirius. Buzz would stop when needle went back up. Torque converter locking and unlocking randomly on the Interstate. After about twenty minutes, the 'GEN' light comes on. OK, it's toast, at 157k miles. Worse things can happen. That evening, my son drives me to Advance Auto, and I buy a new Remy brand alternator. The next day, car's in the garage, heat is on, I pop the hood, and I find that the negative terminal is cracked, giving intermittent connection. The arc burns inside the terminal suggest that some sparking was happening. A quick inspection may have saved about $150, but now there's one less thing (hopefully) to go wrong! But, as we found out a few years ago, the alternators that are regulated by the engine computers don't like running without a battery in the loop, due to dirty terms, so maybe the new alternator would have been needed anyway.
 
Serpentine belt tension on the 4.0 is 180-200 ft lbs NEW. Used belt (after 15 minutes of operation) is 140-160 ft lbs.
 
1. Inspect your belt. This could be a belt issue. If the belt is glazed, old, (more than 60k) replace it! Goodyear Gatorback is a good replacement belt. And know that the belt on the 4.0 needs to be pretty darn tight to work efficiently and keep quiet.

2. The voltage regulator is in play here. Especially when the voltage rails high on your voltage gauge.

The voltage regulator is inside of the computer.

Voltage regulator is inside the alternator 1984-1998.

1999+ is in the PCM
 
Voltage regulator is inside the alternator 1984-1998.

1999+ is in the PCM

Pretty sure that 91-01 XJ 4.0, the voltage regulator is part of the PCM.

Just checked a 1993 FSM that verified that is true for a 93, and I would imagine that earlier HO (91-92) is the same as well as later models to 2001.

Someone please confirm. TX
 
i stand corrected.
 
Sorry for the slow update. Re-installed cleaned alternator yesterday. All seems well. Voltage gauge is at 14 where it should be. I drove it to work this morning with no problems. I hope this took care of the problem. I guess time will tell. As far as the voltage regulator, the guy that cleaned the alternator said that it is part of the PCM on this model and if need be, we could bypass that and put a voltage regulator on the alternator. This would cause the gauge not to work and thus make the "check gauges" light stay on. Hopefully that's not the problem. By the way, thanks Joe for the belt tension. Where can I buy a belt tension gauge? I stopped at Autozone last night and they do not sell them.
 

A similar problem occurred for one of the members of our group during a recent trip to Afton Canyon when we crossed a flowing river that was over 3' deep.
We had to disconnect their battery and pour water on the alternator to wash the mud out of the rotor and stator.... After sitting for a hour or so for lunch the alternator was back to charging again....
 
The Nippon-Denso alternators used 91-01 are regulated by the PCM.
 
Day 2 and the alternator is charging fine. Funny thing is I haven't been off road in this jeep in 2 years. The guy did say that it was full of mud though. Guess if just started messing with the alternator. Thanks for the help and suggestions everyone!
 
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