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  1. #1
    Ollie
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    No Power to Fuel Pump - Help Please!!!

    Hi,
    I'm having some problems working out why I'm not getting a power supply to my fuel pump. Any suggestions on what to check would be very welcome!
    So far I've checked the fuse (No. 23, as well as all the others), switched the fuel pump relay, switched the main relay and even switched the motronic ECU with a spare I have. No of these have made any difference.
    I've checked the fuel pump itself isn't faulty (took it out of the tank and hooked it up to a battery directly - works fine!).
    I also checked that the fuel lines are clear, not that this would have any effect on the power supply to the pump, but may have been the source of the problem.

    I can't think of anything else to check!
    Please help!
    Ollie

    1989, 520i 12v auto
    247,000 miles!


  2. #2
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    Member No: 33986 glen-sj is an unknown quantity at this point glen-sj's Avatar
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    Re: No Power to Fuel Pump - Help Please!!!

    Have you tried bypassing the fuel pump relay to power the pump directly.* To run the fuel pump, remove the relay and connect the socket for relay terminal 30 to the socket for relay terminal no. 87 with a fused jumper wire.* If the pump does not run with the jumper installed, the fault could be in the fuel pump or* the wiring to the pump. Remove jumper wire.*

    Check the pump and its wiring as described:Remove the fuel pump relay and operate the fuel pump as described above.* The fuel pump should run.* The fuel pump should run.* If the fuel pump does not run, disconnect the harness connector form the pump.* With the jumper wire connected as described above, check the positive (+) battery voltage at terminal 5 and ground (-) at terminal 4. If voltage and ground and are present, the fuel pump is probably faulty. If there is no voltage, check the wiring from the fuel pump relay and make sure the relay is functioning correctly

  3. #3
    Big Dog
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    Re: No Power to Fuel Pump - Help Please!!!

    It might be the crankshaft position sensor. Until the ECU gets a signal from the CPS, it won't turn on power to the fuel pump.

  4. #4
    Ollie
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    Re: No Power to Fuel Pump - Help Please!!!

    Checked the fuel pump, it works fine. I've also jumped the terminals of the fuel pump relay - no effect. I haven't checked if there's a positive and an earth at the fuel pump electrical harness yet though. If it turns out that there's a fault in the wiring, then how the hell could this just happen?? It was running fine (though admitedely it ran out of petrol (!) as I'd been working on it in the gararge for a few weeks), but I filled it with a couple of gallons straight away and now the pump won't run.....unless I take it out of the tank and hook it up to the battery directly.
    Could a fault in the wiring circuit develop like this?
    Also, how do you go about checking the crank shaft position sensor?
    Cheers guys!

  5. #5
    Big Dog
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    Re: No Power to Fuel Pump - Help Please!!!

    If you ran it out of fuel it may have damaged the pump itself because it uses fuel as a coolant for the electric motor. Removing it from the tank and testing may have jarred it enough to get it to run but it may now be pulling too much current for the existing wiring. Try this, remove the access plate in the trunk (boot), turn the car to the start position and rap the pump assembly with a hammer (use the wooden handle and give it a sharp tap). If it begins to run you may have a bad pump with a burned section in the coil. Also check for power at the pump connector. I'm willing to bet there IS power there and the pump was damaged due to lack of fuel.

  6. #6
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    Member No: 68743 mixgasdivr is an unknown quantity at this point mixgasdivr's Avatar
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    Make SURE you're jumping the fuel relay!!

    I had a 94 M50tu with the same problem...if you just look at the photo in the Bentley Manual of where the fuel relay is in the e box you might be jumping the wrong relay.

    I followed the pic, which showed the fuel relay in the middle of the three. Mine ended up being all the way inboard (toward the driver), so for two days I was actually jumping the main relay which was the middle one.

    Fuel relay has four prongs, main has five. There are also specific color wires that go to the fuel relay to differentiate it from the other 4 prong relay in the cluster. Depending on your model e34, look at the Bentley electrical diagram section.

    Hope this helps.

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