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  1. #1
    Active Member Two Rings
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    Dec 28 2017
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    Poland

    Audi S5 V8 4.2l (CAUA): fuel return line

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    Hello,

    Is it possible that the S5 with V8 (2008-2011) has no fuel return line to the fuel tank?

    It looks like there are three lines from the fuel pump/tank only:

    1. Fuel line
    2. Breather line
    3. Vaccum line

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  2. #2
    Senior Member Four Rings b7_Andy's Avatar
    Join Date
    Jul 18 2015
    AZ Member #
    343342
    My Garage
    Scrap Transmissions!
    Location
    Denver, CO

    That is correct, Audi doesnít not use a return fuel system in the B8 S5, it uses a high pressure fuel system where instead of the low pressure fuel pump running at constant 12V supplying the engine with constant fuel, it is controlled by a fuel controller above the tank and runs at varying voltages to send only the exact amount of fuel needed to the fuel rail... the fuel is then pressurized again at the fuel rail by the two high pressure fuel pumps before it is injected directly into the cylinders (not the manifold). I believe there is also some sort of pressure regulation in the filter for the low pressure fuel pump (at least itís like that in the B7 direct inject systems). And I think in the S5 the fuel filter is located in the fuel tank.

  3. #3
    Active Member Two Rings
    Join Date
    Dec 28 2017
    AZ Member #
    411678
    Location
    Poland

    Thanks!
    Ok so... if I deactivate the fuel pump in a tank (by fuse) and put the main supply line to a can with a chemistry (injectors cleaner), do the hight pressure pumps suck the cleaner?

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  4. #4
    Senior Member Four Rings b7_Andy's Avatar
    Join Date
    Jul 18 2015
    AZ Member #
    343342
    My Garage
    Scrap Transmissions!
    Location
    Denver, CO

    Quote Originally Posted by Silv3r View Post
    Thanks!
    Ok so... if I deactivate the fuel pump in a tank (by fuse) and put the main supply line to a can with a chemistry (injectors cleaner), do the hight pressure pumps suck the cleaner?

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    I donít know how well that would work. The car definitely wouldnít run like that and with no signal from the low pressure fuel pump it would probably just keep the injectors closed and I donít think the high pressure pumps would move any fuel.

  5. #5
    Active Member Two Rings
    Join Date
    Dec 28 2017
    AZ Member #
    411678
    Location
    Poland

    Any1 else with the answer?

    The question is:

    If the mentioned two HPFP are able to pump/suck the cleaner from the can or the cleaner have to be applied under some pressure to the HPFP?

    I want to give a chance for Tec-2000 before replace the injectors :)



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