Charging Question

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Jun 8, 2015 | 11:14 AM

godspeedcig

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Charging Question

I have a 2001 5.4 Expedition and recently it stopped charging the battery. I had replaced both the alternator and the battery 2 years ago but took them both to be tested. Turns out the battery was bad, so I replaced it again. After reassembly, I noticed that when at idle with nothing turned on (no lights, radio a/c, etc.) the voltage will periodically jump to about 14.5V for a short period, then return to about 12.2V+. It seems to be cycling. When I put it under a load with lights, radio, a/c, it jumps to 14.5 and remains at that voltage.

Is this normal?

Jun 9, 2015 | 12:06 PM

alloro

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Originally Posted by godspeedcig

Is this normal?

No it is not normal. There is a problem either with the commuter rings/brushes in the alternator or the voltage regulator. Was it a brand new alternator that you installed or a rebuilt one?

Jun 9, 2015 | 12:49 PM

godspeedcig

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I installed a new alternator 2 years ago, not rebuilt. But it just tested good. I suppose it could be intermittent and didn't show up when tested. Is there anything else that could be causing the fluctuations?

Jun 9, 2015 | 01:42 PM

alloro

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Quote:

Originally Posted by godspeedcig

Is there anything else that could be causing the fluctuations?

Just one that I know of, a loose engine to body ground strap/wire.

Jun 9, 2015 | 03:14 PM

godspeedcig

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Thanks for the help. So if I jumper the alternator housing to the neg battery post would that be a valid test to check that possibility?

Jun 9, 2015 | 03:52 PM

pdqford

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Quote:

Originally Posted by godspeedcig

Thanks for the help. So if I jumper the alternator housing to the neg battery post would that be a valid test to check that possibility?

Yes. But use a voltmeter. Positive lead on the alternator frame and negative lead on the negative battery POST (not on the negative cable's clamp.) That will tell you if your alternator is properly grounded.

With the engine running about 1500 rpm and the headlights, heater blower(s), etc. on high you want to read <0.2 volts DC if your grounds are good.

Here's where of I speak:
https://www.ford-trucks.com/forums/1...or-issues.html

Jun 9, 2015 | 04:43 PM

alloro

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While you're in there doing what pdqford said, just to be thorough also test the negative battery post to the body to make sure that jumper is good too. Just like the alternator to the battery negative post it should read less than 0.2 volts.