Rebuilt alternator and still only 12volts! wtf?

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  • 2002maniac
    R3V Elite
    • Feb 2005
    • 4260
    #1

    Rebuilt alternator and still only 12volts! wtf?

    i picked up an 87 325is today and the guy said the battery was bad so I threw in my optima and it started right up and purred like a kitten. I noticed that the battery idiot light was still on so I checked the system voltage with a multimeter and it showed just under 12v. It should be quite a bit higher so I figured the alt was bad, however, the guy i got the car from said he just had the alternator rebuilt in april. now suspicious of this "rebuild" I pulled the regulator and checked the brushes but they looked fine. Finally I yanked the alt and took it to autozone to have it tested. Their machine passed it with no problems.

    Anyone have a similar problem before?
    Any suggestions?

    my next plan is to pull all the cables and test for resistance. Anything I'm not thinking of?

    Thanks guys!
    Tags: None
    • jlevie
      R3V OG
      • Nov 2006
      • 13530
      #2
      Since the alternator tested good when out of the car, the prime suspect becomes the connections for. Check both ends of the larger wire that runs from the alternator to the starter and the engine ground strap.
      The car makes it possible, but the driver makes it happen.
      Jim Levie, Huntsville, AL

        Comment

        • LovableSheep
          Wrencher
          • Dec 2007
          • 246
          #3
          I had the ground strap come loose on mine, stopped charging the battery. It still looked like it was connected, but it was loose enough to not be making a proper connection. The idiot light never came on though...that would have saved me some hassle if it did.

            Comment

            • SpecM
              R3V Elite
              • Oct 2005
              • 4531
              #4
              +1 check all connections + grounds
              1989 cirrisblau-metallic 325i

                Comment

                • 2002maniac
                  R3V Elite
                  • Feb 2005
                  • 4260
                  #5
                  Well, i got this figured out on friday. I checked for resistance through all the cables, grounds, and other connections. Fired it up and still only 12 volts. Next i pulled the voltage regulator out of my 318is and swapped it in. BOOM!! 14.2V

                  I guess this teaches us not to trust the tester at autozone :shifty

                    Comment

                    • SpecM
                      R3V Elite
                      • Oct 2005
                      • 4531
                      #6
                      Originally posted by 2002maniac
                      I guess this teaches us not to trust the tester at autozone :shifty
                      -no, the tester was right! It wasn't charging until you fixed the alternater
                      1989 cirrisblau-metallic 325i

                        Comment

                        • 2002maniac
                          R3V Elite
                          • Feb 2005
                          • 4260
                          #7
                          I pulled the alternator off the car and took it in to have it tested. They said it was charging when it was not! Then i switched out the regulator and fixed it.

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