Intermittent Battery light - Ford Powerstroke Diesel Forum
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Old 10-19-2008, 04:47 AM
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Intermittent Battery light

Alternator?
Truck starts ok when its warm outside(GPR is shot, don't know that this is related to that though....) Voltage reads fairly normal at start up(13.5 or so). On a 1 hour trip the voltage will slowly drop to about 11.5v and Battery light comes on. Let truck sit a while(overnight) and it will start with normal voltage.
With my cheapo batt/alt. tester that I have, the Alternator tests low, batts test great. Is there a better way I can test the alt., or just take it to auto zone and get it tested? Its been years since I've had problems with an alternator, that I forget all the signs of it. I don't want to kill my charging system....Would this problem have anything to do with my GPR being bad?

Any thoughts on this?
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Old 10-19-2008, 05:18 AM
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The only way this might be affected by your GPR is if the GPR is stuck in the closed position, which would draw a good amount of current and cause your alternator voltage to drop. My advice would be to pull your alt and have it checked at the auto parts store. If you have a Napa around, I would consider buying from them, but not AutoZone unless that was the only choice.
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Old 10-19-2008, 05:27 AM
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I was just going to go to Auto zone to get it tested, I know they'll do it for free....Not sure where I will buy from yet.
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Old 10-19-2008, 09:36 PM
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i would bet 90% sure alternator.
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Old 10-20-2008, 01:13 AM
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I am having the same problem, I just bought two new batteries about two months ago. When I first start it up it is fine but a few miles down the road I get the battery light and after a few more miles it goes away? Any ideas?
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Old 10-20-2008, 01:19 AM
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The batteries drain as the engine and other auxiliary components are on, the alternator is there to make up for this discharge and if it is not operating properly it will show a discharge on the batteries. Not sure why it shows proper voltage at start up but if it is showing discharge while running, it would almost have to be alternator. Don't think the GP would have any affect since it is only used at start up.
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Old 10-20-2008, 03:12 AM
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Quote:
Originally Posted by FordCowboy View Post
The batteries drain as the engine and other auxiliary components are on, the alternator is there to make up for this discharge and if it is not operating properly it will show a discharge on the batteries. Not sure why it shows proper voltage at start up but if it is showing discharge while running, it would almost have to be alternator. Don't think the GP would have any affect since it is only used at start up.
The highlighted part I knew....that's why it didn't make sense to me either about the start up volts?

Weird... yesterday I went out to start it up, KOEO-13.2v, start it up and with KOER-it goes up to 14.0v until I get on the road and it steadily goes downhill again to like 11.6v or so.....
Everything poiints to the alt. except that it is somehow recharching itself overnight?

Well I'm going to have it tested today and i'll post back, i'm pretty sure thats what it is though.....

Thanks guys
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Old 10-20-2008, 11:45 AM
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Alright, I brought the alt. down and got it tested....bad, as expected.

Put the new one in....problem solved, voltage stays up an no battery light.

Thanks guys
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Old 02-02-2009, 09:46 PM
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hello every one,
i'm new at this but i was looking to see if i wasnt the only one with a battery/alternator problem. i'm on my 3rd alt. and 2nd set of batteries
i seem to have the problem where my 04 X diesel starts fine and alt puts out about 14 volts but as i drive with in the half hour it drops to 12.6 once i get to work about an hour later the meter reads 13-13.1. with the engine off the batteries read about 12.8 and from one day to an other they hold charge making me belive that the batteries are good. what can make the alternator start out good and as the days go by voltage output from it drops little by little until is not putting out enough to replenish the batteries and kill them? that's how i'm ending up with a 3rd alternator replacement and 2nd set of batteries. any help is appreciated i dont want to have to buy a 4th alternator and 3rd set of batteries
thank you all
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