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Thread: Fuel pump won't prime, works when plugged to 12V directly

  1. #1
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    Fuel pump won't prime, works when plugged to 12V directly

    The car is currently sitting as I'm waiting for a refurbished turbo to arrive, in the meantime I took the ECU out since I was going to get a chip on there and wanted to see if it's chipped already. Changed the battery and took the fuel pump out to check whether it's an aftermarket one as I was considering upgrading. After my thorough inspections the pump stopped priming when I turn the key
    Can't exactly go to start the car to check but I don't it would work as it always primed before.

    Checked the wiring, the plug, everything seems connected. I checked the wires with a multimeter and I was reading 12.5V on the red wire and around 7.5V on the green (before the blue plug going to the fuel pump). I also checked the corresponding wires on the other side and it's the same.
    I expected to see change in voltage on one of the wires (ECU signal? don't know which wire tho) when I turn the key for when the fuel pump would normally prime but nothing.

    Could anyone explain to me which wire is for what and what kind of voltage I should expect to get on them when I turn the key?

    The fuel pump worked when I tested it out of the car with a car battery.
    I tried jumping the relay (not sure if correctly) by bridging connector 2 and 3 and it still didn't prime.
    Tried grounding the fuel pump elsewhere with no luck.

    I'm a total noob with wiring, don't know if the wiring is bad or I managed to damage my ECU or something...
    Any help to guide me how to diagnose this problem would be greatly appreciated.

  2. #2
    Guest norfy's Avatar
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    you will damage the ecu if you put power down the black/pink stripe wire on the back of the relay.

    you need the ecu and cas connected for the pump to prime as well.

  3. #3
    aka Jeffries Limitless Imports's Avatar
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    Ecu makes the ground connection for the pump to prime. If it's not working but was all ok before I reckon you have damaged the ecu

  4. #4
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    Quote Originally Posted by wilq View Post
    I tried jumping the relay (not sure if correctly) by bridging connector 2 and 3 and it still didn't prime.
    Why you do that?

    Green and blue relays 1-2 is the coil. One end of the coil is connected to the ECU. The other goes to the fuse and battery via ign switch and fusible link.

    Pins 2-3 are nearest the EGI relay (furthest from front of car), both connect to 12V from the battery via fuse, ign switch and green fusible link at front of the row.

    To operate pump jumper relay terminals 3-5, they are the 2 that are closest together and furthest from the latch. Cease and desist from messing with the terminals next to the latch while the ECU is plugged in.

    Fuel pump gets 12v on black/yellow wire and ground on black wire. These are left and right of plug and next to the latch. The other back wire on the plug is the ground for low fuel switch.

    If pump doesn't prime with jumper on terminals 3-5 and ign in "on" position. Connect a bulb on the pump plug. Jumper relay terminals 3-5. If bulb doesn't light check fuse and fusible link.

    When you get pump to run with jumper refit the relay and ECU. Make sure the ECU plug screw is fully tight and then use a screwdriver to seat plug fully, working down both sides at about 4 places each side. If the pump doesn't prime you need a voltmeter. Put the +ve probe in the back of the ECU plug on pin 18 and the -ve probe to ground. Switch on, there should be 0V for the priming time and then 12v.

    Does it have an alarm? The most common 2nd circuit is the fuel pump. Other than the last thing you have messed with the next most common source of problems is with what alarm installation monkeys messed with.

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