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2.5 V6 TDi (AFB) run out at 1/4 tank

Discussion in 'A4/S4 forum(B5 Chassis)' started by Looney540, Jul 7, 2013.

  1. Looney540
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    Looney540 Member

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    [Jul 7, 2013]
    Hey guys

    My A4 always "run out of fuel" at half a tank even when there was actually half a tank of fuel. My in tank fuel pump failed and on getting a second hand pump (whole thing) it has literally just run out at 1/4 of a tank. Can anyone explain this?

    Is it possible that something that lifts fuel from the other side of the tank, as it's a Quattro has failed maybe?

    Would really appreciate any help.

    Many thanks.
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  3. wesmaster
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    wesmaster Member

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    [Jul 7, 2013]
    Balance pump in tank failed, all it does is make sure that both sides of tank are equal.
    Got one kicking around for an A6 allroad somewhere. Cost £280 from Audi. Check part numbers!
    #2
  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 7, 2013]
    AFAIK there is no actual in tank pump on these cars?

    They use a siphon jet thing to move fuel from one side of the tank to the other.

    Maybe the sender has been disturbed when the pump unit was swapped?
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  5. Looney540
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    Looney540 Member

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    [Jul 8, 2013]
    How do you mean? I just changed the in tank pump!

    I didn't do enough miles to use half a tank, so I can only assume the gauge is reading correctly when it shows 1/4 of a tank.

    It most definitely had 1/2 a tank before the pump was replaced now it ran to a 1/4 and ground to a halt.

    Something must be causing this?

    I saw an advert for an A8 than ran out at 1/4 or something and it was the jets not lined up?

    Wesmaster - Where is the balance pump located so I can check part numbers?

    Thanks
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  6. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 8, 2013]
    Do you have a pic of the "pump" you changed? I'd be interested to see it, because as far as i know, there is no pump? The injector pump on the engine simply "sucks" fuel from the tank, and the part in the tank is just a swirlpot?

    As i said above, B5 quattros dont have a transfer pump, they use a suction jet arrangement which sits on the return line, and siphons fuel across from one side to the other. I guess its possible you might have dislodged this assembly when you changed the pump, however the fuel sender is in the part of the tank where the "pump" resides, so if the siphon wasnt working, the fuel guage would show empty.
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  7. Looney540
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    Looney540 Member

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    [Jul 8, 2013]
    Hi mate,

    This is the old "pump" (or what I thought was the pump) that was removed.

    ImageUploadedByTapatalk1373292734.832924.jpg

    Whatever this is wasn't getting fuel to the engine but the replacement does. As I said, it has solved my 1/2 tank issue is also fixed but I now have this 1/4 a tank problem!

    Your help is appreciated my friend.

    Niall
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Jul 8, 2013]
    Yeh thats a pump alright.

    Would have to have a look at the pipe layout to see what exactly it was doing, the pump outlet appears to be Y'd into a line that returns to the base!?
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  9. Looney540
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    Looney540 Member

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  10. wesmaster
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    wesmaster Member

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    [Jul 11, 2013]
    The Balance pump on a allroad is under right hand side rear seat, looks like your picture TBH. But you've changed it already?
    Bit of a weird one that.
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  11. boost-addict
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    boost-addict Active Member

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    [Jul 11, 2013]
    im looking at a a4 v6 tdi which has the same problem, i was thinking the same, problem with transfer of fuel.

    is it easily fixable?
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  12. Looney540
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    Looney540 Member

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    [Jul 11, 2013]
    The one I changed it for was second hand, the whole thing was changed. Is it possible that the balance pump was already fubared on the second hand pump?
    #11
  13. boost-addict
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    boost-addict Active Member

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    [Jul 12, 2013]
    Well it was possible for your pump to be ****. Whats to say the one you bought was the same. Maybe thats why they sold it. If you buy s/h again which isnt a problem to be fair considering the price of a new one. Try to buy from a genuine top rated seller. Theres plenty of vw/audi breakers on the bay that give guarantee. Any way hope you get it sorted.

    But think you may have solved your own mystery
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  14. boost-addict
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    boost-addict Active Member

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    [Jul 12, 2013]
    Ignore, asked question in my own thread
    Last edited: Jul 12, 2013
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  15. Looney540
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    Looney540 Member

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    [Jul 12, 2013]
    I see your point but I found if very difficult to find one online and at any breakers, turns out my mate had one in a garage from a petrol model.

    I just wish I knew what other models used the same pump so I could find another.
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  16. boost-addict
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    boost-addict Active Member

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    [Jul 12, 2013]
    whats the part number on the one you have or your old one
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  17. Looney540
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    Looney540 Member

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    [Jul 12, 2013]
    Ill look in the morning mate.

    Thank you though.
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