Alternator over charging?

Tiny
RWOSR1
  • MEMBER
  • 1999 FORD EXPEDITION
  • 4.6L
  • V8
  • 4WD
  • AUTOMATIC
  • 142,000 MILES
I discovered that the alternator was charging at14.8V on a full load. (Everything turned on) I changed it out with an old one I took from the same vehicle, and it is over-charging at 17.9V with a full load.

I suspect the voltage regulator on each one, but I wonder if it could be anything else. Like maybe a PCM issue?

If you have any ideas, I'd like to hear them.
Sunday, October 22nd, 2023 AT 9:07 PM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,138 POSTS
These vehicles had problems with the plug at the alternator so I would look at that first to check for melted connectors. Next, check the engine ground to battery and then the battery to chassis ground. It does not look like the PCM is involved in the charging system, here are the alternator wiring diagrams so you can see how the system works. Check out the images (below). Please let us know what happens.
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Monday, October 23rd, 2023 AT 8:04 AM
Tiny
RWOSR1
  • MEMBER
  • 9 POSTS
Thank you for responding! I will look closely at these items and let you know what I find. There are two wire conditions I can think of that are questionable and in line with your suggestions.
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Tuesday, October 24th, 2023 AT 4:40 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,138 POSTS
You are welcome, please let us know how it goes.
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Tuesday, October 24th, 2023 AT 8:22 AM

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