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  1. #1

    Low Voltage at Fuel Pump

    HELP!!

    I have a 2008 GTI SE 155. I've been chasing an issue related to loss of power at 3800 rpm.

    I pulled the fuel pump and replaced both filters. When I reinstalled it, the pump would not run. I removed the pump assembly and inspected the wiring, but everything looked fine. So, I decided to connect the pump terminals directly to the battery and it spun right up.

    Re-installed the pump in the tank and tested the voltage on the pump harness. With the key on, the voltage was only about 12.2 V--compared to 12.8 V if I test from the + harness connector to battery ground.

    I pulled the main relay and performed voltage test between Relay Fuse Box B4 and A6. Voltage here was 12.5 V--still less than the 12.8 V found between B4 and Battery Ground.

    I disconnected and tested resistance on the DESS post and everything tested less than 1 ohm.

    Next, I did the Fuel Pump Harness connectivity test indicated in the Shop Manual. Test resistance between Main Fuse Box A1 and ECM B29. The manual shows that should read 12 ohms. I am only showing 3.5 ohms on this test. I assume that the majority of this 12 ohms would be from the pump itself.

    How can I isolate the voltage issue in the Relay Fuse Box?

    Does the low resistance reading on my fuel pump indicate a bad pump?


  2. #2

    Low Voltage at Fuel Pump

    Low resistance could be as a result of a short inside the pump. The voltage would drop due to the direct short to ground . Similar to the voltage drop when the starter motor is engaged.

  3. #3
    Quote Originally Posted by Tintman20 View Post
    Low resistance could be as a result of a short inside the pump. The voltage would drop due to the direct short to ground . Similar to the voltage drop when the starter motor is engaged.
    I agree, but I can't get past the fact that the pump motor was working before I changed the filters and it works now if I connect it directly to the battery. I guess it's possible that the pump has been partially faulted all along, but I would like to also eliminate the voltage problem on the harness before I invest $360 on a new fuel pump.

  4. #4
    JT jpt7779's Avatar
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    http://greenhulk.net/forums/showthread.php?t=272608

    read this thread especially post #22.

    You can bypass the OEM fuel pump wiring completely with a relay setup. Your issue is common and easily corrected with the relay Setup in post 22 or by using Riva's relay kit, either setup will work as desired.

  5. #5
    Quote Originally Posted by jpt7779 View Post
    http://greenhulk.net/forums/showthread.php?t=272608

    read this thread especially post #22.

    You can bypass the OEM fuel pump wiring completely with a relay setup. Your issue is common and easily corrected with the relay Setup in post 22 or by using Riva's relay kit, either setup will work as desired.

    Can I buy the RIVA relay kit separately or only with their fuel pump? I did not see that option on their website...

    I can probably build relay kit myself, but like having everything pre-packaged.

  6. #6
    That looks to be more related to people running high powered pumps. Your N/A engine shouldn’t require that much amperage. It may fix the issue but I believe it’s overkill and eventually the real problem will reappear. Possibly pump failure or other.

  7. #7
    Quote Originally Posted by Tintman20 View Post
    That looks to be more related to people running high powered pumps. Your N/A engine shouldn’t require that much amperage. It may fix the issue but I believe it’s overkill and eventually the real problem will reappear. Possibly pump failure or other.
    Shouldn't be necessary on an NA engine, but it does seem like a poor design in that a short in the pump could pull too much current thru the ECM and cause damage.

    More than likely, I will need a new pump also, but I think adding a relay like this will be an improvement to the original design.

  8. #8
    Quote Originally Posted by Tintman20 View Post
    That looks to be more related to people running high powered pumps. Your N/A engine shouldn’t require that much amperage. It may fix the issue but I believe it’s overkill and eventually the real problem will reappear. Possibly pump failure or other.
    Shouldn't be necessary on an NA engine, but it does seem like a poor design in that a short in the pump could pull too much current thru the ECM and cause damage.

    More than likely, I will need a new pump also, but I think adding a relay like this will be an improvement to the original design.

  9. #9
    JT jpt7779's Avatar
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    Quote Originally Posted by LargeJohn View Post
    Can I buy the RIVA relay kit separately or only with their fuel pump? I did not see that option on their website...

    I can probably build relay kit myself, but like having everything pre-packaged.
    You can get the relay at any auto parts store with some quality wiring and do it your self much cheaper.

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  11. #10
    Already located the relay on Amazon.

    Is the Walbro GSS342 a good replacement for my OEM fuel pump? Definitely more volume that I will ever use, but they seem to holdup.

    Also, would this pump fit the housing in my 2008 or will I have to do some mods?

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