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alternator?

DurbElites

NAXJA Forum User
Location
Simi Valley
on my 89 xj 4.0 my gauge for the battery reads very low at idle and when i hit the gas or am cruising it will sit where it should but when i am at idle it will drop again to almost nothing. but the weird part is after driving for about an hour at idle it will read normal. i went through all the grounds and wires but it changed nothing so is it time for an alternator?
 
DurbElites said:
on my 89 xj 4.0 my gauge for the battery reads very low at idle and when i hit the gas or am cruising it will sit where it should but when i am at idle it will drop again to almost nothing. but the weird part is after driving for about an hour at idle it will read normal. i went through all the grounds and wires but it changed nothing so is it time for an alternator?

First and foremost - back-check your IP voltmeter with a "known good" DMM - the panel gage (especially on RENIX) is a notorious liar... You could be just fine, but having an instrument error.

5-90
 
I dont think its the gauge because my lights will dim also when it drops and the battery is not that old.. maybe like a year old. but i will check with my volt meter to make sure about the gauge.
 
DurbElites said:
I dont think its the gauge because my lights will dim also when it drops and the battery is not that old.. maybe like a year old. but i will check with my volt meter to make sure about the gauge.

You should be at least at 13.5volts, most likely your alternator. If you can pull it you can have the unit bench tested for free at most Kragen shops, Pep Boys/whatever.
 
unrealtrip said:
You should be at least at 13.5volts, most likely your alternator. If you can pull it you can have the unit bench tested for free at most Kragen shops, Pep Boys/whatever.

Search up my posts on that subject. Consider them authoritative - I wasted three and a half years behind the counter at various Kragens...

While that bench will give you voltage generated, it does not tell you the current generated - which means you could be getting 14VDC @ .1A. Oops - that's not enough to run a cellphone.

If you're going to get the thing tested, look up a rebuilder in your area, and take it there. You may end up paying a couple bucks for the test, but their benches damn sure do test current output (and voltage, and ripple check, and...) and you're going to get a much better idea of what you're looking at.

And, don't buy from a "chain" store, either. They pay about 15-20 cents on the dollar, and buy them by the Conex box from overseas. They offer the "Lifetime Warranty" as a gamble - they're betting you won't need it, you're betting you will. You will, eventually (and I'm not talking years here - I'm talking 4-6 months, on average.)

Short form - take your alternator to a rebuilder to test. If it's bad, buy from that rebuilder - you're dealing with the man who does the work, and you probably won't need his warranty. You may end up paying more, but it's worth it (I've been dealing with my rebuilder - and sending him business - for so long that I pay him less than I would at Kragen's - and I get to watch him test the unit before I take it. Solid!)

One of these days, I want to find out who was in charge of purchasing the rewinds I used to have to take back, whack him over the head with a case of frozen tractor parts, and leave him in the meat freezer...

5-90
 
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