Low charging voltage. Alternator or Voltage Regulator?
I have a 97 5.9L Laramie 4x4 with about 215k miles.
Lately when I start my truck the voltage gauge shows around 12v, and the GEN light will come on. After driving a bit sometimes the voltage will jump up to its normal 14v, but not always. I've checked the voltage at the battery with a multi-meter, and it is in agreement with the gauge reading. My question is how to distinguish whether the problem is the alternator or voltage regulator. Should the alternator always put out 14v and the regulator adjusts the charging voltage to the battery, or will the output of the alternator vary based upon regulator control? FWIW, I have never replaced either alternator or ECU, but I've only had the truck since it was at 185k. From general appearance both could be OE. TIA |
Check/clean all connections first. Might be as simple as a loose connection somewhere. (PCM or Alternator.)
If that all looks good, best bet is to yank the alternator, take it to the parts store, and have it tested. |
Check and make sure that your serpentine belt tensioner is working properly.
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Originally Posted by HeyYou
(Post 3282385)
Check/clean all connections first. Might be as simple as a loose connection somewhere. (PCM or Alternator.)
If that all looks good, best bet is to yank the alternator, take it to the parts store, and have it tested. |
A good alt rebuild shop and some auto parts stores will have a jig that they mount your alt into, spool it up and check the output.
Many moons ago, I had a truck that would have similar problems as yours. Batt light would come on at low rpm's and be fine at higher rpm's. Turns out it was an-almost broken wire. At the higher rpm's, the engine would torque to the side enough to complete a good electrical connection. A idle, the connection would be piss-poor. |
Thanks all. I will definitely look at all connections and wires.
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Keep in mind, the voltage regulator is in the PCM, so, check those connections as well. :D
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Back to part of the original post. Should the output of the alternator be a constant voltage, or does it vary with demand? Stated in a different way should the voltage at the alternator output always match the charging voltage at the battery?
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The pcm should regulate the voltage but i am not sure where it does this, whether internally in the alt or externally. Someone else will chime in.
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Originally Posted by brewman
(Post 3282406)
Back to part of the original post. Should the output of the alternator be a constant voltage, or does it vary with demand?
The easy way to get started is to haul the alternator out and take it to someone who can bench test it. If you've got, say, open diodes in the rectifier, which would one of the failures consistent with what you've described, the bench test will show that. If the thing checks out on the bench, then it's time to resume troubleshooting. |
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