voltage bouncing around

Over the past few weeks, to a month, I've noticed the volt meter will jump from 10v-16v. When this happens the lights dim, ect... So I'm sure the gauge isn't messing up. It dosen't do it constantly, just a couple minutes then stops. Today however, it did it constantly all the way to work. Any ideas on what could be wrong? A loose ground/connection maybe? What would be the best way to troubleshoot this? The truck is under warranty, I might just take it in, but would rather not have to pay the deductable. Any help would be appreciated.

opps, The truck is a 2000 2wd 4.8L with mods listed in signature.

check your belt tensioner....

When exactly is it doing this? I've noticed from the time I bought mine (used w/25k) that mine's done the same thing.

Only does it when I stop at at a sign or light. Dash lights and headlamps dim. If I don't give it any gas, it'll come back up to normal on its own. If I give it gas, it immediately comes back up. It dips to about 12. Had the alt checked out ok.

I've talked to others IRL and here - some never see this and others have seen it from the time they bought theirs new.

belt is a godd chance cut another symptom loose belt would be overheating and of not overheating poor performing A/c (which you wouldn't notice [winter]) could be an alternator problem though have a checkers or autozone check it for amp output with a VAT machine(hope they can help you alot of the people employed there don't know how to use it)good luck and keep us post it

I just replaced the belts (serpentine and AC) about a week ago. Both of the old belts looked good, but the AC belt would squeak any time there was moisture in the air. It hasn't squeaked since being replaced. So, maybe a loose tensioner for the AC, but that should not effect the alt. I will take the alt to Autozone, have it checked.

The voltage will fluxuate the most just after the truck is started, engine cold. It will bounce around after it is warm sometimes, also.

I haven't noticed any connections to the fluxuations with turning on certain lights or blowers, so I'm guessing the problem is under the hood, or with an actual wire/connection.

Please, let me know if you figure this one out. I'm at a loss as to what the cause is. Your situation sounds pretty damned close to mine.

I was wrong (and corrected it) about how far down it was dropping - its dipping to about 12. And only doing it when the engine's cold from what I can recall. Doesn't matter if the heater or A/C is running or not.

took the truck in today. I should get an answer by Monday. I'll keep you guys up to date. Thanks for your suggestions.

You get an answer on this yet, or are they still looking at it?

Turns out a diode on the voltage regulator on the alternator was bad. They replaced the alternator, everything is working great now.

Side note, I had the dealer look at my rear quater windows, because they were leaking air.... They want $750 to fix. They said the seals were bad, but to replace them the entire window needs replaced. I passed on that deal.

The alternator was $241 at the dealer, I would recommend napa, autozone, ect.. for that repair.

Why didn´t they just change the diode? we do that down here all the time...

probably because it was under warranty. I wasn't aware that it could be replaced on its own.

Thanks for the reply. I had AutoZone check the alt. According to them, it read good.

Guess I'll be taking my truck to an honest-to-goodness alternator shop, spend the $13 to have a full diag done by the pros and make sure.

If anyone in the Austin area needs it, Texas Alternator will do a full diag for about $13.