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Fuel system test issues with jumping relay, OBC related?

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    #1

    Fuel system test issues with jumping relay, OBC related?

    I am trying to troubleshoot my fuel pump and I am unable to get the fuel pumps to turn on when jumping the fuel pump relay. I have a fused switch and wire to trigger the fuel pump and I tried jumping pins 30 and 87 as directed by the Bentley manual for fuel system tests.

    I have read that it may have something to do with the 13 button OBC fuel lockout. I can't seem to find any real information on how to bypass the relay or its location. Some places say it is under the drivers dash, others put it above the ECU.

    Any help would be appreciated. I am trying to determine if my in-tank fuel pump is functioning properly. My external pump is pretty loud and I want to be able to test both for pressure and flow. I need to be able to fire the fuel pumps for 30 seconds to do the fuel system tests as per the Bentley.

    I do get voltage at the intank pump, and the car does run just fine. I am just trying to hunt down the cause of an intermittent stall under load. It feels like a fuel cutout as the engine stops pulling for a second and the rpms drop. Feels like a fuel system issue.
    sigpic
    1987 325e Lachssilber w/ MarkD chip and late bumpers, Zender EVO spoiler, s3.25 LSD

    Originally posted by nando
    I don't think there's really strong evidence that ZDDP harms cats.
    Tags: None
    #2
    Might be easier to wire in a 12v LED that you can watch operate while you drive.

    Comment

      #3
      Page 1360-1 here shows the fuel pump relay directly wired to the fuel pump and controlled via a ground thrown at the ECU...

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      http://wedophones.com/Manuals/BMW/1988%20BMW%20325%20-%20325i%20-%20325is%20Electrical%20Troubleshooting%20Manual.pdf


      Test to see if you are getting 12v at the relay.

      EDIT: Most sure way to excite the fuel pump is a direct 12v on the pump connector itself.
      john@m20guru.com
      Links:
      Transaction feedback: Here, here and here. Thanks :D

      Comment

        #4
        Page 6581-1 shows the OBC relay wiring. The OBC relay module, black box above drivers knee, immobilizes the car by cutting power to fuel pump and disabling spark by eliminating control voltage to the ECU. There's a picture on 7000-5, figure 5, of the relay. I know there is a way to bypass it, I just have not found a clear instruction on how to do it.



        I know there is some way to disable it. I guess I will just try running power direct from the battery with an inline fuse.

        Originally posted by ahlem View Post
        Might be easier to wire in a 12v LED that you can watch operate while you drive.
        I tested the voltage with the car running at there is 12v at the in tank pump.
        Last edited by itsonlygeorge; 10-26-2016, 10:20 AM.
        sigpic
        1987 325e Lachssilber w/ MarkD chip and late bumpers, Zender EVO spoiler, s3.25 LSD

        Originally posted by nando
        I don't think there's really strong evidence that ZDDP harms cats.

        Comment

          #5
          You could always just setup a fuel pressure test gauge T'd into the fuel rail supply line and drive around with the gauge facing you through the windshield, prop it under the windshield wiper.

          HF have a good set that has everything you need: http://www.harborfreight.com/catalog...=fuel+pressure

          ..even cheaper if you can snag a 20% discount coupon.

          And yes it's accurate, checked against a Snap-On unit.

          Comment

            #6
            The OBC relay has 2 green connectors with about 6 to 8 wires going to and from it. The 2 largest wires are the green and green/red. To bypass the relay just spice or jumper the green and green/red wires together.

            Comment

              #7
              Originally posted by RobDog View Post
              The OBC relay has 2 green connectors with about 6 to 8 wires going to and from it. The 2 largest wires are the green and green/red. To bypass the relay just spice or jumper the green and green/red wires together.
              This is how I have always done it, never had to do any fuel pump wiring in the race cars.

              Originally posted by itsonlygeorge View Post
              Page 6581-1 shows the OBC relay wiring. The OBC relay module, black box above drivers knee, immobilizes the car by cutting power to fuel pump and disabling spark by eliminating control voltage to the ECU. There's a picture on 7000-5, figure 5, of the relay. I know there is a way to bypass it, I just have not found a clear instruction on how to do it.



              I know there is some way to disable it. I guess I will just try running power direct from the battery with an inline fuse.



              I tested the voltage with the car running at there is 12v at the in tank pump.
              Perhaps I am missing it, but I do not see the fuel pump or relay on pages 6581-x, but it does show the signal wire from the OBC to ECU (ECU grounds the fuel pump relay when it sees CPS signal, and can turn it "off" if a code has been set) - and it shows the fuel level sender in the tank.

              Also see pg. 1360-6 where the fuel pump power goes right from the battery junction, to relay, then c101, then fuse and finally pump.
              john@m20guru.com
              Links:
              Transaction feedback: Here, here and here. Thanks :D

              Comment

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