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Suburban alternator and maybe charging system problems...

suburbandadof4suburbandadof4 Member Posts: 2
edited May 2014 in Chevrolet
Good evening to all, I am new to the forums.
I come with a question, but first some background.

I very much like Suburbans, I've owned 3 total. Currently own 2, an '89 K1500, and a '95 1500 2wd. My first was a '75 2500 2wd with a 454. I do all my own maintenance on them, Not to dis any mechanics out there, but I can't afford to pay a mechanic, plus I, for the most part, enjoy working on my own cars. Okay, so now the question.
My '89 had a problem with the A/C idler pulley, the bearing seized. After replacing it I noticed that the charging system wasn't working. I had the alternator tested, it was good. I cleaned the terminals to the battery, checked all the grounds that i could see. I also put in a new battery, and cleaned all the connections at the alternator. Still it's charging the battery with it running. I used a multimeter to test it, at idle it was showing 12.51VDC, when I would rev the engine the voltage would drop. My other Burb at idle shows 14.71VDC at idle.

Anybody that has had any experience with this kind of electrical gremlin, please (pretty please) let me know what other areas I need to look at.

Thank You.


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    kiawahkiawah Member Posts: 3,666
    Have the alternator tested somewhere different.
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    suburbandadof4suburbandadof4 Member Posts: 2
    I swapped the alternator out of my my '95 to make sure. Even with a 'known good part'
    my meter only showed 12.45VDC at idle.
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    kiawahkiawah Member Posts: 3,666
    The only thing I can think of without pulling out electrical schematics, is to check both of your main + and - battery cables and connectors on both ends. You could have a bad ground, or internal cable corrosion. While the engine running, I'd check to see if any voltage drops from battery - to engine ground. And then check from battery + to main buss fuse.
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    theironmantheironman Member Posts: 1
    Chevrolet / Goodwrench only run the engine to 2000RPM for alternator tests. My Silverado SS has had an issue with dimming lights, rough idle for about 1½ year now.

    After picking up my truck and getting the same recording that everything was fine, I had started it up there at the dealer and let it idle for about 2 mins, then ran it at 2500 for about 30 secs when the anomaly happened.

    The service advisor checked it out and took it back for for more testing. The 1st two tests were at the standard procedure 2000RPM....when they were told to rev it up to 2500, BAM!!! FAILED!!! dipped to 11.5 volts at 2500 RPM!! Explains why the issue would present itself after being on the fwy for a time.

    I think GM designed these tests to prevent never considering real world speeds, either that or they know that the likelyhood of failing at 2000RPM is nill and save them lots of $$$ in warranty replacements. 2000RPM basically equates to 55MPH.

    Unless you're driving in Hawaii, this is not a valid test value period!!!

    A year and a half and two different dealerships -- same test, same results. It's stuff like this that really turns me off to continuing to purchase GM products in the future.
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