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Thread: E38 Fuel pump relay control while cranking

  1. #1
    New Member
    Join Date
    Oct 2019

    Default E38 Fuel pump relay control while cranking

    Hi all,

    I am wondering how to replicate the fuel pump relay staying on while the engine is cranking?

    I have a stand alone setup with an E38 running an L77. I know the fuel pump will run for 2 -3 seconds when the ignition is initially turned on.

    If commanding the starter replay externally from the ECU, will the fuel pump run from the low rpm signal it sees from the crank angle sensor? Or should I use a diode protected feed from the start relay to the fuel pump relay to make the pump run while cranking?

    Thanks in advance for your thoughts,

  2. #2
    Joe (Moderator) joecar's Avatar
    Join Date
    Apr 2003


    Hi Des,

    The ECM will run the fuel pump as long as it sees the crank position sensor

    i.e. fuel pump will run during cranking (ECM has cranking fuel tables).

    If ECM is not pulling the fuel pump relay, then there is a fault which neefs to be diagnosed.

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