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Thread: Fuel Pump Electrical Diagnosis Help

  1. #26
    Join Date
    Sep 2008
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    Santa Barbara
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    91 Dinan860 & 91 850 6sp
    Do you have continuity between pin 1 on the DME plug and contact 85 on the fuel pump relay? If not, there's your problem... grounding pin 1 on the DME has to energise that relay when everything is plugged in...
    '91 Dinan 860 Stage III (soon to be Dinan TT 6L)
    '91 850i 6sp (mint)
    '91 850i 6sp (getting there)
    '90 Dinan 750iL TT stage III
    '94 850 CSi (being restored to factory perfect)
    '94 840ci (4 short - obvious parts car), '91 850i parts car
    '73 3.0 csi, '08 535i, '95 318i
    ...and a few other non BMW cars

  2. #27
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    Report:

    Checked continuity from pin 1 to pin 85 - no continuity. Which begs the question, how does pin 85 get 1.58vdc? Does this wire go through something else on it's way to pin 85? Is 85 getting a partial ground from something else?

    Made a jumper wire, pin 1 to 85.

    Voltage w/o jumper 1.58vdc

    Voltage w/jumper .13vdc.

    Swapped DME's, problem did not move.

    Wow! I'm really lost now. Not that I wasn't before.

  3. #28
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    I hope I haven't stumped everyone. I am totally lost on why this car is doing this. I don't know what do do with it...

    Please help!

  4. #29
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    91 Dinan860 & 91 850 6sp
    you have a broken wire. The minimal noise reading you're getting is likely through the EGS unit, which is also tied to that line... forget that.
    The wire you need to trace goes from pin #1 on DME 1-6 to pin 4 (FUEL PUMP Relay Socket #85).
    It isn't a particularly long run, so it should be easy enough to trace.
    You might find it does have a splice (X8036) where the EGS unit ties in, but other than that it is a pretty short hop from the ECU (DME) to the relay socket.
    Brown wire with a Green stripe...

    Your tests above are a bit odd... try this... make a jumper from pin #1 on the DME 1-6 and put the other end directly to contact 85 on the FUEL PUMP Relay socket. Plug the relay in and crank the car, or plug your meter into 85 & 86 and crank the car. You should see 12v across the relay socket on the meter, or see the relay energize with it plugged in. If so, find your break in the wire described above
    '91 Dinan 860 Stage III (soon to be Dinan TT 6L)
    '91 850i 6sp (mint)
    '91 850i 6sp (getting there)
    '90 Dinan 750iL TT stage III
    '94 850 CSi (being restored to factory perfect)
    '94 840ci (4 short - obvious parts car), '91 850i parts car
    '73 3.0 csi, '08 535i, '95 318i
    ...and a few other non BMW cars

  5. #30
    Join Date
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    Hampshire UK
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    99 840ci Sport Indv
    I think you need to stand back and have a good think of how you got here! In this thread:

    https://www.bimmerforums.com/forum/s...ver!-Maybe-Not

    ...your car was running fine, and that was only August.

    I also think you are poking the wrong pins of the DME and possibly the wrong pins of the wrong relays - that is the only explanation for the results of the tests you have performed so far. A good bit of time spent working out what is where and what your original problem was would be useful - because at this rate you are going to link the wrong parts of the electrical system together and frizzle something in a very expensive way!

    Stand back, retrace your steps and explain how you got from a fully running car to a completely dead one.
    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 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

  6. #31
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    TT Cayenne / SC 850
    do both pump work when you apply voltage to the carrier directly??

  7. #32
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    Timm;
    Thanks for the reminder. When the car ran in August, Ithink it was running on 6 cylinders. Why it wasn't throwing a code or something on the display is kind of curious. As for getting right socket, I have a real-deal shop manual and always verify before I jump into electrical as to what is where. I have sone experience with volts/ohms etc, but it goes back 52 years. Rust never sleeps.

    Cartoonz;
    Ran the latest jumper test.
    Keyoff = .07vdc.
    Keyon = .07vdc
    Keyon + crank 12vdc +-

    Gotta wire to replace. Oh joy!

    Seems you are right re: broken wire, but there is no keyon voltage to prime the pump.

    Huh?

  8. #33
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    Update;

    Can someone tell me which harness plugs into DME 1-6 and which for DME 7-12?
    It was plugged in like this. Front harness to DME 1-6, rear harness to 7-12.

    When tracing the brown w/green tracer, I found it going from pin 1 of DME 7-12 to pin 4/85 of relay of 1-6 fuel pump relay vs pin 4/85 of the 7-12 fuel pump relay.

    Is it possible, some PO-S reversed either the DME connectors or the relay bases?
    Could that be the problem?

    Told you this car was boogered up...

  9. #34
    Join Date
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    91 Dinan860 & 91 850 6sp
    No guarantees which DME sits where, and it really doesn't matter... but whichever harness hooks to the corresponding relays, that's which side it is... perhaps you've been measuring from the wrong DME?
    That said, I think Timm makes a good point...
    Obviously, what you *thought* was DME 7-12 is really 1-6
    Last edited by cartoonz; Today at 02:10 PM.
    '91 Dinan 860 Stage III (soon to be Dinan TT 6L)
    '91 850i 6sp (mint)
    '91 850i 6sp (getting there)
    '90 Dinan 750iL TT stage III
    '94 850 CSi (being restored to factory perfect)
    '94 840ci (4 short - obvious parts car), '91 850i parts car
    '73 3.0 csi, '08 535i, '95 318i
    ...and a few other non BMW cars

  10. #35
    Join Date
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    I was basing relays, DME's etc. On factory diagrams from shop manual.
    The 0 fuel pressure was going into the 1-6 fuel rail. It may not matter which DME is which, but it may matter which connector goes to which relay. The factory diagram shows, from front to back.
    1-6 fpr
    7-12 fpr
    1-6 DME-relay
    7-12DME -relay
    DME 1-6
    DME 7-12
    EML

    Trying to trace all the brown w/green tracer. The is a 3way splice and a black 4 connector (3 used) with 2 each brown green tracer and 1 brown only.

    If they are connected wrong. I need to figure out what's right, then work from there. It's hard to troubleshoot this when you start with a trainwreck

  11. #36
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    Okay, now that I am checking the correct pin 1 to the correct pin 85, I do have continuity (about 4 ohms resistance). I'm going to try the jumper and see what happens.

    I'll be back...

  12. #37
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    Update:
    Jumper pin 1 on 7-12 to correct pin 85 on 7-12 relay
    Keyoff .26
    Keyon 1.58
    Crank 1.58

    Continuity = yes

  13. #38
    Join Date
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    Hampshire UK
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    99 840ci Sport Indv
    Back where we started - almost! Crankshaft sensor at the top of the list....
    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 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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