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Non Running S3 - Fuel Pump Not Running?

Discussion in 'A3/S3 Forum (8L Chassis)' started by Racehunter, Jan 10, 2014.

  1. Racehunter
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    Racehunter New Member

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    [Jan 10, 2014]
    A friends S3 (1999) suddenly stopped, as it would have it, right outside his office!. Anyway, it is now sitting in my workshop and it appears the fuel pump is not running. Now, I do not post blindly (knowingly that is) and have searched the forums across the WWW for some information relating to wiring diagrams etc, as an aid to the problem solving. However, I have not actually found that much useful (to me) information.

    I have exposed the fuel pump, and given it a little 'hard stick' persuasion to no avail. I have checked fuse 28 and all is good. I have also put a meter to the pump harness plug and without the benefit of any wiring info, come to the conclusion that the 2 outer wires (of the 4) are for the pump while the inner are sender related. I also assume that the outer brown is earth and the outer blue/red is 12v supply. Now this is what I have seen on the meter:

    Ignition on - .02V
    Cranking - 9.1V

    How does this system work? does it wait for pressure to be sensed in the fuel rail before switching on an 'ignition live' supply through the relay or what. Now I appreciate that this might be the correct figures (although 9V seems somewhat low to me) and the problem is a failed pump, but without further information, I am loathed to play the 'replace if not sure' fitters approach to repair.

    Any suggestions would be gratefully recieved especially on the voltage readings at the pump. Also circuit information for the relay to enable me to test that item and is there any such thing as an 'auto off' fuel switch in case of accident and if so, have these been known to fail.

    Anyway, many thanks for reading and hopefully replying.

    Cheers

    Steve
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  3. Racehunter
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    Racehunter New Member

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    [Jan 12, 2014]
    Doesn't anyone have a wiring schematic for the fuel system? Or a link to one? Really need to understand why there is such a voltage drop at the pump connector.

    Steve
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