Fuel Pump Hardwire
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This is a discussion on Fuel Pump Hardwire within the Engine Performance forums, part of the Tutorials & DIY category; This modification was motivated by my need to completely bypass the PossumLink ECU and OEM fuel controller, since the Link ...

  1. #1
    Registered User pace's Avatar
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    Fuel Pump Hardwire

    This modification was motivated by my need to completely bypass the PossumLink ECU and OEM fuel controller, since the Link ECU exhibits a bug on some vehicles whereby it randomly terminates the signal to the pump. However, these directions are applicable also for stock-ECU'd vehicles, if for example you just want to run a cleaner power feed to your fuel pump.

    These directions are as performed on the WRX wagon, and may differ very slightly for a sedan.

    You will need:

    - 1 x Single Pole Double Throw relay (will be marked with terminals #85, #86, #87, #87A, #30, and will probably be rated at 20A/30A).
    - Inline 20A fuse.
    - 10 gauge wire.
    - 14 gauge wire.
    - Male spade connectors.
    - Bullet connectors.

    Steps:

    1. Remove the rear bench seat. There are two 12mm bolts to remove, and then the seat will pivot up at the front and then pull free.
    2. Remove the driver-side and passenger-side trim pieces that run below the doors. Do the same for the driver-side rear trim piece.
    3. In the side of the passenger footwell (behind the trim piece you just removed) find the green 4-wire connector that plugs into the white fuel pump relay, and disconnect it.
    4. Find a location in the engine bay, in close proximity to the battery, where you can mount the relay. I put mine under the washer bottle which necessitated removal of the bottle ( 2 x 10mm bolts).
    5. Find the wire from relay connection #87A, and remove it or cut and insulate it. It is not used, but will be hot when the car is switched off.
    6. Find the wire from relay connection #30, and fit the inline fuse. Then affix a ring terminal and connect this to the +ve battery terminal.
    7. Find the wire from relay connection #85, and ground it at the chassis point next to the battery.
    8. Find the relay connection #87, connect the 10 gauge wire, and route this through the rubber grommet behind the brake pedal, and route it along the door sill (under the trim) all the way to the rear seat area.
    9. Find the relay connection #86, connect the 14 gauge wire, and route this through the rubber grommet behind the brake pedal, then behind the console across to the green fuel pump relay connector in the passenger footwell.
    10. Fit a male spade connector on the 14 gauge wire, and push it into the green connector for the female terminal that corresponds to the small Green/Red wire. This is the 12v switched ignition source to power the relay coil.
    11. On the passenger side under the rear bench, find the fuel pump harness. This is a two-wire translucent connector that consists of Black/Red and Black wires on the fuel pump side, connecting to Black/Orange and Black/White wires. Disconnect the harness.
    12. On the aforementioned harness, cut the Black/Red and Black wires close to the connector.
    13. Find a suitable grounding point for the fuel pump Black wire, connect a ring terminal, and ground it. You may need to extend the wire to reach an appropriate grounding point.
    14. Use a bullet connector to connect the 10 gauge wire that was run from relay #87 to the fuel pump Black/Red wire.
    15. Insulate everything with electrical tape, and replace the rear bench, and trim pieces etc.

    Now when you turn the ignition to the full on position, the pump will continuously run (no two/three-second prime) at 100% duty cycle. The car should start as normal.

    This method completely bypasses any influence over the fuel pump by the ECU and the OE fuel pump controller (a good thing if you run the PossumLink 44S).

    -Pace

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  3. #2
    Registered User Austin's Avatar
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    The only drawback to this method is that if you stall, or for some other reason the egine dies with the key remaining in the ON position, your fuel pump continues to operate.
    TEC3 & VF34

  4. #3
    Registered User pace's Avatar
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    Originally posted by Austin
    The only drawback to this method is that if you stall, or for some other reason the egine dies with the key remaining in the ON position, your fuel pump continues to operate.
    Correct. Just as it does if you turn the key to the ON position but don't engage the starter.

    Since the WRX has a fuel system with a return line, and since the pump itself has a built-in fuel return system, the only adverse mechanical effect this could have is running your battery flat if you are foolish enough to sit with the key in the ON position without the motor running.

    In the case of an accident; the fuel pump can continue to run anyway in some cases. Unfortunately I know this from personal experience.

    -Pace

  5. #4
    Registered User is2scooby's Avatar
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    In my stock car the fuel pump seems to run for a couple of seconds and stop (assuming this is to prime the lines for startup) and does not continue to run when the key is left in the on position.

    Maybe I'm not listening closely enough.

    Thanks for the write-up Pace, you're always a wealth of information!
    Aloha, Richard...
    Retired Moderator
    TXS Stage 4 UTEC + TMIC + JoeP
    12.75 @ 105.67mph - 1.74 60'

  6. #5
    Registered User Austin's Avatar
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    Originally posted by is2scooby
    In my stock car the fuel pump seems to run for a couple of seconds and stop (assuming this is to prime the lines for startup) and does not continue to run when the key is left in the on position.
    In your stock car the fuel pump does run for a couple of seconds and then shut off. That's the initial priming sequence, controlled by the fuel pump controller. One of the (minor) drawbacks to hardwiring the fuel pump (removing the fuel pump controller from the circuit), is that you lose the 3 second fuel pump priming sequence. As soon as you turn the key to the ON position, the fuel pump starts, and doesn't shut off.
    TEC3 & VF34

  7. #6
    Registered User phast's Avatar
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    Pace,
    Finally got around to doing this mod. So far so good.

    I wanted to add to the section where you cut the fuel pump harness under the seat. I found it wasn't necessary. I just unplugged the harness and used spade connectors to plug into power and ground for the terminal.

    Just a nice touch so there is no cutting of factory wiring.
    -jay
    i drive a jeep n stuff.

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