2005 Chevy Avalanche alternator issues

wolfsmane

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Make
Chevy
Model
Avalanche
Year
2005
Miles
198000
Engine
5.3l
I have a 2005 Chevy Avalanche LT 5.3l. It has the 145amp alt on it.

Here is the issues I am having - About 14 months ago, battery wasn't holding a charge. Replaced it with new one. Then that one was getting weak, turns out the alternator was failing, but not dead. Replaced alternator with ACDelco and new belt.

Last week driving along and noticed that my volt gauge was dropping and got the idiot light for low voltage. So, bought a new ACDelco alt and installed it and had the battery charging overnight. Battery charged fine. Been driving the truck a few days and today get the idiot light and dash dinging telling me that it was not charging again. Was close to home and just got in.
Did I just get unlucky and get a bad alternator? Or should I be looking elsewhere for another issue causing the alternator to fail?

A couple of weeks ago doing routine maint and noticed the neg battery terminal was not staying tight. Took it off cleaned the eyelet to looking brand new and put a new battery lug nut/screw in it. So, I have a good tight ground. Checked the positive and it was tight also.
Used a multimeter and cranked up the truck, tested between the negative battery post and the positive lug right on the new alt and it was showing that it is only putting out 11.95v.

Advice please
 

billr

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Sure, it is possible you got a bad one. Take it off and into your local FLAPS for testing.

All output from that alt comes from that stud on the back side, and goes through a "fusible link" wire that acts as a last-resort fuse. That wire is usually connected from the alt output stud to the battery-terminal connection on the starter. Check that wire for signs of damage or burning.
 

wolfsmane

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I don't see a fusible link. It comes from the alt stud to this red box between it and the battery and splits off to the starter.
 

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billr

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That wire from the alt to red box is likely the fusible link. It is pretty small for 145A, there will be heating in the wire even under normal operation.

Check voltage (engine running) at that alt stud. if that is still low, <14V, then the alt is bad or it isn't getting proper control through that 4-pin connector. We could search for info to force field excitation to see if the alt itself is OK, but that is probably more bother than just taking to your FLAPS for test.
 

billr

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That wire from the alt to red box is likely the fusible link. It is pretty small for 145A, there will be heating in the wire even under normal operation.

Check voltage (engine running) at that alt stud. if that is still low, <14V, then the alt is bad or it isn't getting proper control through that 4-pin connector. We could search for info to force field excitation to see if the alt itself is OK, but that is probably more bother than just taking to your FLAPS for test.
 

wolfsmane

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That wire from the alt to red box is likely the fusible link. It is pretty small for 145A, there will be heating in the wire even under normal operation.

Check voltage (engine running) at that alt stud. if that is still low, <14V, then the alt is bad or it isn't getting proper control through that 4-pin connector. We could search for info to force field excitation to see if the alt itself is OK, but that is probably more bother than just taking to your FLAPS for test.
The volt on that alt stud is 11.95v like stated above. I will be taking to get it checked this morning. Thanks for the help
Pull that box up and open it.

Which box, the red one? It is open in the picture.
 

billr

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Sorry, I saw that you had measured at the alt stud, but forgot. Take the alt for a test before we try getting into the control wiring. Or if you have a schematic of the alt/charging wiring, post the schematic.
 

wolfsmane

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Checked the alt out at the part store and it is only putting out 11.50v, so tested bad.

Put a brand new alt on and fully charged the battery and it seems to be running good, showing that it is putting out around 14v on the dash meter. Haven't had the chance to drive it any distance yet to find out if it will stay at being good.
 
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