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Thread: Voltage Drop

  1. #1
    Join Date
    Jan 2016
    Location
    Honolulu
    Posts
    2
    My Cars
    2003 BMW 325i Wagon

    Voltage Drop

    Hello All,
    I have a voltage drop in my 03 e46 wagon
    Voltage at the jump points under the hood is 14 at idol
    voltage at battery in rear at battery is 12.4 at idol
    battery light flickers intermittently and sometimes drains the battery.
    When flickering voltage under the hood remains 14 and drops as low as 10.7 at the battery as it drains. Then lights, radio etc flicker and work intermittently.
    Revving the engine does increase the voltage under the hood to about 14.5, but it remains low and unchanged at the battery. (12.4 to 10.7 depending on how low the battery charge is getting)
    Battery is a new NAPA Legend EGM.
    Terminals clean and tight.
    The main positive wire at the battery gets quite warm. (seems to indicate another problem to me, but Im not sure where.)
    Main ground at battery to the body was sanded and cleaned with electrical cleaner. It is tight.
    Any suggestions?

    Thanks,

    Brad

  2. #2
    Join Date
    Apr 2009
    Location
    Chattanooga, TN
    Posts
    9,073
    My Cars
    '94 MX-6
    Sounds like a bad alternator.
    Current: '94 MX-6 V6/5 • '72 240Z • '10 Mazda5
    Past: '02 330i/5 • '85 RX-7 GSL-SE • '95 540i/6'95 525i/5'86 635CSi/5 • '88 JZA70 • '86 4K quattro • '85 RX-7 S
    Wish list: Type 44 • Manta • Pre-'85 CGT • 405 Mi16 • SVX • W123 Coupe

  3. #3
    Join Date
    Aug 2014
    Location
    Lawrence Kansas
    Posts
    1,236
    My Cars
    2004 325XI/2008 GL320
    Sounds to me like you have a corroded ground strap or a battery with a parasitic cell. I would clean all main grounding points and both terminals at the battery. Loose connections drop voltage, make resistance, and create heat.
    Last edited by dhurley34; 01-28-2016 at 08:34 AM.

  4. #4
    Join Date
    Jan 2016
    Location
    Honolulu
    Posts
    2
    My Cars
    2003 BMW 325i Wagon
    Turns out a past owner had done a electrical repair using a hose clamp to the main wire running from the firewall to the battery.
    Not good. That connection beginning to fail was responsible for the main wire at the battery being hot.
    The spot of the repair was much worse. totally burned through the insulation and melted the plastic interior panels. Just not through the the upholstery, so it was not visible until disassembling all the interior panels on the passenger side of the car. Lucky I didn't burn up the car with a significant fire. The mechanic I had check it out used a donor harness from a parts car to replace that portion of the cars wiring. (firewall to battery)
    Not so cheap... but problem is now fixed.
    I think the next time I have a voltage drop, I will be right on disassembling to expose the wiring and potential problems.

    Thanks for your responses to my original post.

    Brad

  5. #5
    Join Date
    May 2020
    Location
    USA
    Posts
    1
    My Cars
    BMW E34
    See voltage regulator

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