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Thread: 2nd parasitic draw post 98 740i pre 6/98

  1. #1
    Join Date
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    86 635csi 98 740i 96 MB

    2nd parasitic draw post 98 740i pre 6/98

    So I checked out mA as suggested but was frustrated with .002 readings on all
    fuse circuits. So before I narrowed what I was not doing correctly and having to amp clamp,
    I read volts from the battery to try and isolate the ign switch.

    Battery full charge, 13.09 volts, battery cables not connected.
    3 days latter 12.89 volts.
    Connected battery cables and disconnected ign switch harness.
    Next day AM 12.2 volts
    2 days latter AM 11.86 volts
    Same day PM 11.67 volts
    Connected ign switch harness
    Next morning 11.31 volts
    2 days latter 8.16 volts

    Now charging battery.
    guess a new switch is to be ordered.



    Any help on confirming and direction before doing an amp test on all those God Damn circuits will be appreciated.

    Bob V
    Last edited by 1986series6; 09-22-2018 at 06:52 AM.

  2. #2
    Join Date
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    99 840ci Sport Indv
    The results are consistent with either battery drain - or - just a battery that has reached the end of its life. At a terminal voltage of around 8 Volts the battery is being permanently damaged very quickly - if it's been at 8V for any length of time it is dead as a dodo.

    Batteries are notoriously difficult to measure to ascertain if they can hold a charge - and with those readings I think I would start with a new, fully charged battery as a starting point, you cannot measure battery drain with a bad battery. I would then do an actual closed-current battery drain test:

    https://www.meeknet.co.uk/E38/E38_Battery_Drain.htm

    You can used a DC current clamp on the negative lead - the latest ones work pretty well as long as they are pre-calibrated (zero the meter when the clamp is next to, but not around the negative lead).
    Last edited by Timm; 09-22-2018 at 04:30 PM.
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


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  3. #3
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    86 635csi 98 740i 96 MB
    Timm,

    Brand new AGM battery. Was fully charged @ 13.09 volts
    This is the amp clamp ( https://pdimeters.com/docs/pdf/manuals/CA-60.pdf )

    I'll use an inline fuse holder with spade connectors to check mA on all circuits

    and I'll follow your sleep instructions. I hope I find high mA on a circuit to fix this PITA.

    Thanks Timm

  4. #4
    Join Date
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    No need to remove fuses - and you mustn't remove them as this resets the 16-minute timer and removes evidence. Instead, use this method:

    http://www.meeknet.co.uk/E64/Fuse%20...20Readings.pdf

    What actually is the current demand after 16 minutes?
    Timm..2007 E64 650i Individual Sport..1999 E31 840ci Individual Sport..ex owner of 2000 E38 740..1999 E38 740i V8 M62..1998 E38 735i V8..1993 E32 730i V8..1988 E28 518i


    My BMW Repair YouTube Channel
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  5. #5
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    OK thanks for the heads up

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