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No power to fuel pump relays.

Discussion in '348/355' started by carwhisperer, Jan 11, 2015.

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  1. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
    Full Name:
    Brian
    #1 carwhisperer, Jan 11, 2015
    I am getting no power to my fuel pump relays after my DIY engine out. I mean no power at all to any of the sockets for either relay. My understanding is that at least one of the sockets, the one that goes to pin 30, should be hot at all times, or at least when the key is turned. And that a second socket, the one for pin 86, should be energized when the key is turned.

    Is it possible that this is being caused by bad Cat temp ECU's? I read somewhere to take them out. I tried disconnecting them and that didn't help the problem. When you remove them do you have to close a circuit?sd

    My car starts up and runs good when I jump power directly to the fuel pumps.
    Brian
     
  2. 348Jeff

    348Jeff Formula 3

    Oct 25, 2011
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    Jeff
    #2 348Jeff, Jan 12, 2015
    Have you checked the 2 fuses as well?
     
  3. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
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    Brian
    #3 carwhisperer, Jan 12, 2015
    Yes.
     
  4. 348Jeff

    348Jeff Formula 3

    Oct 25, 2011
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    Jeff
    #4 348Jeff, Jan 12, 2015
    What about an immobiliser? Ive been caught out before when orking on the car and I've left the key in the ignition and the immobiliser has time out and reactivated so you need to take it off again....?
     
  5. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    13,455
    San Carlos, CA
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    Mitchell Le
    #5 yelcab, Jan 12, 2015
    Bad Cat TCU has nothing to do with it.
    Go back to basics, check battery, battery switch, main power to the relay board.
    Do you have a wiring diagram?
     
  6. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
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    Brian
    #6 carwhisperer, Jan 12, 2015
    OK good to know. I have the factory workshop manual stored on my computer. It is super hard to read with the way the wiring diagrams are broken into parts. Maybe I'll print those pages.
     
  7. Miltonian

    Miltonian F1 Veteran

    Dec 11, 2002
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    Milton, Wash.
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    Jeff B.
    #7 Miltonian, Jan 12, 2015
    I assume you are aware that the engine has to be cranking over at least 30rpm to activate the fuel pump relay (per page C15 of the Workshop Manual). The relay does not activate simply by turning the key to the "run" position.
     
  8. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
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    Brian
    #8 carwhisperer, Jan 12, 2015
    No I didn't know that! Very helpful. Thanks.
     
  9. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
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    Brian
    #9 carwhisperer, Jan 12, 2015
    I'm assuming this function is controlled by the ECU's.
     
  10. Moiluck

    Moiluck Formula Junior

    Mar 20, 2009
    326
    Spain
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    Moisés
    #10 Moiluck, Jan 12, 2015
    You are right, Brian. I had an intermitent power loose in a fuel pump relay due to a failing ECU, causing a misfire in the same cylinder side. The fuel pump relay was clicking on and off like crazy. However, before going to the pricey thing, you would like to check that all sensors connectors are properly plugged and clean; crank sensors, MAFs, idler regulators, pahse sensor and ECUs (behind the seats and through the firewall). For electronics protection, I use to do all the checks with the battery unplugged.
     
  11. carwhisperer

    carwhisperer Formula Junior

    Sep 29, 2014
    426
    Sacramento, CA
    Full Name:
    Brian
    #11 carwhisperer, Jan 12, 2015
    Well things got a little weird. Through some testing I think I have determined that the signal that is delivered to the fuel pump relays is a ground signal, not a + one. While messing around the footwell fuse box I accidentally arced the positive to the ground signal wire. I allowed some of the smoke to escape from the fuse box. Of course I was terrified. My first thought was to try to start the car to assess the damage and it fired right up, fuel pump relays presumably working.

    Then while running it I found that my oil pressure gauge is stuck at 20psi whether the engine is off or on and no matter the rpm. And, it appears that one of my new cam seals is leaking. So yay!
     

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