Battery/Alternator Charging issues

[cabin boy]

The patient: 1999 Jeep Wrangler 4.0 L

The symptoms: The last few weeks while driving the voltage meter will drop down to zero but the charging system was still working (I think!).If I shut the engine off and restart it would go back to normal.Sunday while driving back from the cabin it started doing the same thing, only this time the charging system quit working-by the time I got home I basically had no headlights,dashlights ect..I shut it off when I got home and of course it would not restart. So I threw the charger on it so I could go to work in the morning.I started it up after charging and the voltage meter was working normally. After work I brought it to an auto parts store that checks the battery and alternator for free while it's still on the vehicle. The guy said both the battery and alternator checked out ok. What to do? I'm kind of leery about driving it 3 hours up north! Any help guys?

[jeffreyd]

check for loose ground on the battery, and also on the engine. if you have a volt meter, start the engine put it on the post on the alt and see if it is working, should be around 13 volts or more when charging.

[cabin boy]

I will check the grounds tomorrow evening, when the alt was checked at the store today it was putting out 13.3.

[Big Buck Buster]

The brushes may be getting worn out. Common symptom with worn brushes. Sounds like a new alternator is due.

[BobT]

I'm not sure about the alternator. He said the voltage dropped to zero. With a bad alternator I would expect the voltage to drop to the battery level, not zero. Does it sound more like a voltage regulator problem?

[cabin boy]

Do you know if it has a internal or external voltage regulator?

[Jeremy airjer W]

I think those are regulated by the computer?

The gauge dropping to zero has me puzzled as well.

[jeffreyd]

well it will be an internal regulated alt, have you checked the plug in the back of the alt to make sure that it is not loose? this would be sense wire for computer and also send the ground signal to the gauge.

[cabin boy]

I checked alternator connections-all are solid. The engine ground is tight.If I really reefed on the neg. battery terminal, I could move it-so I cleaned both posts and retightened them. The connectors look like they could be replaced but look to be in pretty good shape overall. The problem is so intermitent it's hard to tell if anything I do helps or not! Next?

[SkunkedAgain]

My opinion is to take it to a real mechanic, not the auto store. You pay the pros to find the hard-to-figure problems and it sounds like your 3 hour drive is worth the $50-$100 service charge.

[cabin boy]

The problem with bringing in into the experts is it is so intermittent,I'm afraid they won't be able to find the problem unless it happens to quit charging while they have it.I have been driving it all week now with no problems!

[Scott K]

The problem with bringing in into the experts is it is so intermittent,I'm afraid they won't be able to find the problem unless it happens to quit charging while they have it.I have been driving it all week now with no problems!

The experts will check the powers and grounds, load test it, check your battery, and test for bad diodes. Obviously it would be better if it was acting up, but they know what to look for.

[SkunkedAgain]

Yeah, I guess my point is that with the (minor) electrical problem you seem to be having, you can ask them to do a quick diagnostic and they might find it. That shouldn't cost an arm and leg while keeping your vehicle idle all day. If they can't find it right away, then keep doing your research.

[cabin boy]

Brought it in and did a charging test-long story short, I had the alternator replaced. Not cheap!