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Bad grounding on 1990 325is?

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    Bad grounding on 1990 325is?

    I assume I have a bad ground instead of alternator due to the following symptoms:

    Battery is brand new, I can put it on a trickle charger and it holds a charge just fine, unless it is hooked up to the car and the car is running.

    My in car volt meter reads at idle 11.8 most of the time, at the battery 12.2 or so. Occasionally it jumps up to 13.5V at both locations for 3-5 minutes randomly, then drops back.

    I have the stock BMW radio, occasionally in the past few weeks it would stop working and display CODE, same as if i had unplugged the battery. Now when I turn it on, it flashes random characters and goes blank. If I leave it on I get a capacitive whine which varies with engine speed.

    Turning on the AC drops the voltage by one volt at idle. This discharges the battery fairly quickly if I keep the AC on, or leave the switch on when I turn of the car. There might be a parasitic drain somewhere else in the system too, but I want to make sure this isn't an alternator/ground issue first.

    The chassis ground strap near the stock oil level sender is still connected to the chassis, though the wiring is a bit worn, there is no jacket on it.

    Since the alternator is capable of putting out 13.5V it has the potential to work. I'm thinking about making a new chassis ground out of a 4gauge wire and some rings, and running a brand new directly off the alternator nut behind the rack and pinon setup to the strut tower. I think there is a ground somewhere in the driver side footwell as well.

    Any suggestions?

    #2
    Sounds like a bad ground could very well be it. Does your battery light in the gauge cluster illuminate at all? If you don't see if ever (like when you shut down your car, it should pop on for a second) then don't forget to check that bulb. It's an obnoxiously integral part of the system.

    Running a ground from the alternator to the strut tower sounds like a messy engine bay. That said I'm a big fan of making new ground straps on old cars.
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    1991 318i Sedan Project

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      #3
      I say your alternator has shat itself.

      Pull it and test it.

      Closing SOON!
      "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

      Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

      Thanks for 10 years of fun!

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        #4
        Originally posted by s_ribs View Post
        Sounds like a bad ground could very well be it. Does your battery light in the gauge cluster illuminate at all? If you don't see if ever (like when you shut down your car, it should pop on for a second) then don't forget to check that bulb. It's an obnoxiously integral part of the system.

        Running a ground from the alternator to the strut tower sounds like a messy engine bay. That said I'm a big fan of making new ground straps on old cars.
        Yep the battery light lights up before I turn it on, if the battery voltage is really low its on as well until I rev the motor a bit. The alternator ground would likely be a termporary thing, if I do that and the car works great then I know its a grounding issue.

        I need to check and see if my alternator is a valeo or bosch, any tips on where to get a rebuild kit if needed.

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          #5
          hah turned out that the alternator belt wasn't tensioned enough, increased the tension and like magic 13.5V at idle

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