Battery light
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Joined: Jan 2003
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From: TX
Battery light
`99 4x4 E.B. Expedition w/ 5.4L and 100K miles.
I have a bit of a weirdness going on. Truck runs fine. No issues. I generally drive it pretty nice. Actually wifey is driving it these days. I've noticed lately, though, that if you get on it, when it cross 4K RPM, the battery idiot light comes on for whatever time you have it above 4K. Back off, shift, or whatever so the RPM drops, and the light goes out. AMP guage never moves or shows issue. Everything else shows fine. I'm wondering if the alternator is spazzing when it's spinning too fast. Thoughts?
I have a bit of a weirdness going on. Truck runs fine. No issues. I generally drive it pretty nice. Actually wifey is driving it these days. I've noticed lately, though, that if you get on it, when it cross 4K RPM, the battery idiot light comes on for whatever time you have it above 4K. Back off, shift, or whatever so the RPM drops, and the light goes out. AMP guage never moves or shows issue. Everything else shows fine. I'm wondering if the alternator is spazzing when it's spinning too fast. Thoughts?
Technical Article Contributor
Joined: May 2004
Posts: 6,509
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From: Georgia on my mind...
The diode assembly is internal to the regulator. An electrical shop could probably replace it for you, but nowadays it's just easier to replace the alternator as an assembly. Usually when diodes start acting funky, you'll get excessive A/C ripple (measured from the battery posts, greater than .5VAC).
Senior Member
Joined: Jan 2003
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Its a fairly common problem,,, I have had 2 high mileage alternators do the same thing. The problem is the brushes have worn down and dont have enough pressure on them to maintain good contact at high rpms.
Some people have replaced the brushes themselves, or you can just buy a rebuild.
Good luck.
Some people have replaced the brushes themselves, or you can just buy a rebuild.
Good luck.
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Joined: Aug 2004
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From: Alberta, Canada
864 is probably right about the brushes. They are part of the internal regulator and are easy to replace for about $15. Since you have to pull the alternator anyway it doesn't hurt to have a look, you could save yourself $300.
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Joined: Jul 2004
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From: oceanside C.A.
Originally Posted by DoobieBrother
`99 4x4 E.B. Expedition w/ 5.4L and 100K miles.
I have a bit of a weirdness going on. Truck runs fine. No issues. I generally drive it pretty nice. Actually wifey is driving it these days. I've noticed lately, though, that if you get on it, when it cross 4K RPM, the battery idiot light comes on for whatever time you have it above 4K. Back off, shift, or whatever so the RPM drops, and the light goes out. AMP guage never moves or shows issue. Everything else shows fine. I'm wondering if the alternator is spazzing when it's spinning too fast. Thoughts?
I have a bit of a weirdness going on. Truck runs fine. No issues. I generally drive it pretty nice. Actually wifey is driving it these days. I've noticed lately, though, that if you get on it, when it cross 4K RPM, the battery idiot light comes on for whatever time you have it above 4K. Back off, shift, or whatever so the RPM drops, and the light goes out. AMP guage never moves or shows issue. Everything else shows fine. I'm wondering if the alternator is spazzing when it's spinning too fast. Thoughts?
kinda funny i just fixed my buddys 99 4x4 E.B. Expedition w/ 5.4L and 100K miles. his alt. would work fine untill around 2500 rpm than it would not charge, we picked up a new one with a lifetime warenty for $135 at autozone, took me about 30 min to pull old one and reinstall very easy to do, good luck