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Thread: 840CI Not starting - How to approach

  1. #1
    Join Date
    Jul 2004
    Location
    Charlotte NC
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    934
    My Cars
    94 840CI

    840CI Not starting - How to approach

    Hey all,

    This is the first time I'll be working on my 840CI (build date 11/93) after coming from the e28 e36 world.

    Currently there is no fuel being provided. I tried swapping out the fuel pump relay with some spare relays, but no luck. It will spark and fire if I use starting fluid. Car ran beautifully before it suddenly didnt.

    I've done some reading, but would like to get some advice before dumping $500+ on a new fuel pump assembly.

    I have read about the crank position sensor, but apparently that will make it not fuel or spark. I do have spark.
    Also read about how a bad passenger side battery could cause this - but very little detail other than word-of-mouth.

    Is there anything majorly common with this build to look at?

    Thanks gents

  2. #2
    Join Date
    Feb 2010
    Location
    Hampshire UK
    Posts
    8,864
    My Cars
    99 840ci Sport Indv
    If you have a spark then the crankshaft sensor is fine. The easiest way forward is to pull the fuel pump relay, pop the cover off (quite fiddly but it doesn't damage the relay), replace it in the socket and then push the contacts across - at which point the fuel pump should run, this can be done with the key out of the ignition. This is the safest way to test the pump.

    The pump is under the rear seat and is accessed by pulling the seats - but you should hear the pump run quite easily without removing the seat.

    Both of the batteries are connected in parallel so one battery does not affect the operation of the pump.

    If the pump does not run check and replace Fuse 23:

    https://www.meeknet.co.uk/e31/Timms_...use_Finder.htm

    Removing the rear seats is covered here:

    https://www.meeknet.co.uk/e31/Panels...eplacement.htm

    Relay finder:

    https://www.meeknet.co.uk/e31/Timms_...lay_Finder.htm

    If the pump does not run during the test and the fuse is good then it will be a failed pump - but just the pump can be replaced from non-OEM sources rather than the whole assembly - more info on that can be found on the E31 forum.
    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
    My Current 840ci Sport Individual
    My Current 650ci Sport Individual
    My E31 Repair and Information Website
    My E38 Repair and Information Website
    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

  3. #3
    Join Date
    Jul 2004
    Location
    Charlotte NC
    Posts
    934
    My Cars
    94 840CI
    Timm,

    Thank you for your detailed reply. Your knowledge and website are unparalleled. I've never tried that trick with the relay before, but darn it that seems so simple! Will report back

  4. #4
    Join Date
    Jul 2004
    Location
    Charlotte NC
    Posts
    934
    My Cars
    94 840CI
    Just an update - removed the cover on a spare relay and manually tested the pump. Dead as a doornail.

  5. #5
    Join Date
    Feb 2010
    Location
    Hampshire UK
    Posts
    8,864
    My Cars
    99 840ci Sport Indv
    Thanks for letting us know - it all helps to give the next member better information!
    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
    My Current 840ci Sport Individual
    My Current 650ci Sport Individual
    My E31 Repair and Information Website
    My E38 Repair and Information Website
    My E63/E64 Repair and Information Website

    Chase - Heroes to a generation

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