Oem alternator slowly died. Replaced with a oreilly rebuilt (in Mexico) unit. At first not really a charge, replaced the battery with a better one and seemed to be fine. Gauge was around the 12v mark, confirmed with my multimeter at 12.5-13.7 fluctuating. But now a couple weeks in the oreilly one is hovering down 10-11 sometimes and other times it does fine. It will work with lights, ac radio on then 20 mins later everything is dimming from just the blinker... Radio cuts off because low voltage. (Aftermarket).

So is there something I'm missing? The alternator should hold the voltage at 13.7 or so solid and not fluctuate correct? I am thinking about taking the oreilly one back. What other options are there? Having the oem rebuilt?

Measure the voltage at the battery with a meter. Have a load test done. Charge voltage is temperature dependent.

I went through several alternators very quickly before finding out that a bad negative battery cable was what was killing them.

For diagnosis, try a voltage drop test.

--Connect multimeter negative lead to alternator case.

--Connect multimeter positive lead to battery negative (-) post.

--With engine running at 1,800 to 2,000 rpm with all lights and accessories on (except rear defogger), check the voltage reading. On the negative side, it should be 0.2 volts or less. If excessive, the connections need cleaning or the negative cable needs to be replaced.

In my case my neg cable had about 0.5V drop. I ran a new cable directly from alternator housing to the battery neg as a quick test, and that solved my problem so well that I left in in place and never got around to replacing the actual battery cable. Been running great ever since, and no more alternator deaths.


http://www.aa1car.com/library/voltage_drop_testing.htm

http://www.4x4wire.com/forums/showflat.p...rt=all&vc=1

More often than you'd expect the newly rebuilt alternator will be bad. that's been my experience anyways.

Ok. New Mitsubishi reman unit.

Everything on at idle inc rear defrost and warm outside charging voltage 13.95
Drop from pos bat to alt pos was 0.29v
Drop from neg bat to alt case 0.09v all using multimeter.

Now dash gauge is pegged at 11v ish but before it would fluctuate. 10-14

A reman from a big box store is a reman, regardless of origin for the original unit. Get that unit re-checked at the store. It should indicate if it's a good unit or not. IIRC it can be done while still on the vehicle.

If it is bad, have them replace it with a good one.

Also if this happens in the future once they've replaced it with a good one, then I'd recommend finding a local shop that specializes in fixing them (via rewind, replacement of diodes, etc.). That's what I did and I no longer have these issues. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Took the oem one to the rebuild shop. He said they can't get parts to rebuild the Mitsubishi labels ones anymore. I trust him so...

New reman is from him, well his supplier. From Mitsubishi Japan reman in America. Looks very very clean/new. The oreilly one was Mexico.

Edit, I tested the first reman on the truck and it was charging 10-13v jumping all over never got to 14v even with no accessories on. I don't have time to swap these out a bunch of times till I get a "good" one.

https://flic.kr/p/wFi6Ea
Pic.