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  1. #1
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    Audi A3 TDI Does not start when fuel less than half a tank

    I purchased an Audi A3 TDI 2006 (BKD engine) around 4 months ago and it developed a fault whereby if the fuel level was below half a tank it would not start. This only happens when the car has been left overnight. It cranks fine but it seems it’s not getting any fuel. It can be started with easy start or when the fuel level is raised again to above half a tank.

    I took it to the Audi dealer and they first diagnosed fuel contamination (oil leaking in fuel perhaps?). Tank was emptied, new fuel filter and fuel lines cleared. Got the car back and same thing happened.

    Again I took it to the dealer and they then replaced the in tank fuel pump. Again the same problem occurred with the same symptoms. There are no fault codes or anything and I believe the dealer hasn’t got a clue what’s wrong.

    Any ideas what it could be? I think it’s definitely a fuel issue but what to try next? Could it be a tandem pump issue? I have read these are prone to failures. I have already spent over £900 on this and still no fix so I want to make sure the next thing I do does fix the issue.

    Thanks for your help.

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  3. #2
    NHN
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    Strange its when lower than half a tank.

    Has the fuel filter been changed ever?

    When you say they swapped the lift pump, did they swap the whole lot or just the main housing or senders?

    Have they checked the fuel line to the filter for pressure when starting?

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    Could tandem pump be causing this?
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    Quote Originally Posted by NHN View Post
    Strange its when lower than half a tank.

    Has the fuel filter been changed ever?

    When you say they swapped the lift pump, did they swap the whole lot or just the main housing or senders?

    Have they checked the fuel line to the filter for pressure when starting?
    The fuel filter was changed twice within a few months. Once for a service and then when they said there was a fuel contamination.

    I believe it was just the fuel pump assembly and sender unit + seal IIRC. I will have to check the invoice again.

    They said the fuel pressure was fine, I guess they must have tested it?

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    NHN
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    Yes but tandem gets pressure from lift pump/filter, so why only with half a tank it does it happen, as pressure isn't based on the tank level, its based on the pump afaik.

    Hey I wouldn't discount it, strange fault tbh.

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    If the fuel pump is working I would say it could even be the fuel senders giving you a wrong reading? ie: could be that your half way showing up meant there was no petrol left? Had a similar issue on my TT, what's your mile range displaying on the dash? If this matches your need then you can tick that off..

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    Quote Originally Posted by Clawdi View Post
    If the fuel pump is working I would say it could even be the fuel senders giving you a wrong reading? ie: could be that your half way showing up meant there was no petrol left? Had a similar issue on my TT, what's your mile range displaying on the dash? If this matches your need then you can tick that off..
    Unlikely as its runs when fine even when under half a tank fuel but just doesn't start when left overnight for a period of 12 hours or so.

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    NHN
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    Quote Originally Posted by Clawdi View Post
    If the fuel pump is working I would say it could even be the fuel senders giving you a wrong reading? ie: could be that your half way showing up meant there was no petrol left? Had a similar issue on my TT, what's your mile range displaying on the dash? If this matches your need then you can tick that off..
    Also unlikely as he already advised the lift pump which includes the level senders has been changed, unless the wiring for the senders is damaged, but unlikely.

    Humour me, disconnect the fuel line to the filter over night, so its open to air, then in the morning reconnect it & see if it starts then, don't forget to reconnect it or you'll regret it, lol.

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    Have you checked the the fuel filler cap rubber seal is in good order?

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    Quote Originally Posted by NHN View Post
    Also unlikely as he already advised the lift pump which includes the level senders has been changed, unless the wiring for the senders is damaged, but unlikely.

    Humour me, disconnect the fuel line to the filter over night, so its open to air, then in the morning reconnect it & see if it starts then, don't forget to reconnect it or you'll regret it, lol.
    I can try but it is currently being driven at the moment so will try at the weekend. Whats are thoughts about trying this?

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    Quote Originally Posted by MrLapou View Post
    Have you checked the the fuel filler cap rubber seal is in good order?
    Have not notice anything, will have another look.

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    Quote Originally Posted by keenu View Post
    Have not notice anything, will have another look.
    Try leaving it parked nose up overnight. I had a starting fault on my car and it was traced to a faulty valve in the lift pump. If you left the car over a long weekend it could be hard to start. Leave it parked nose up overnight and it would also be hard to start.

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    Quote Originally Posted by chinnyhill10 View Post
    Try leaving it parked nose up overnight. I had a starting fault on my car and it was traced to a faulty valve in the lift pump. If you left the car over a long weekend it could be hard to start. Leave it parked nose up overnight and it would also be hard to start.
    Yes I noticed that when it was parked in my drive as its on a slight incline. Looks like fuel is not going to the of the engine. I think i might just bite the bullet and replace the tandem pump.

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    Sounds like you could have an air leak in the fuel line that is causing the fuel to run back in to the tank when left for a period of time. I had this with mine once.

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    Quote Originally Posted by TDI-Tuning View Post
    Sounds like you could have an air leak in the fuel line that is causing the fuel to run back in to the tank when left for a period of time. I had this with mine once.
    Thanks, how did you resolve it?

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    I just had to run down the pipes and find the hole. The pipe had been rubbing on something. try getting someone to turn the engine over and see if you can find any leaks or a sucking noise.

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    Quote Originally Posted by TDI-Tuning View Post
    I just had to run down the pipes and find the hole. The pipe had been rubbing on something. try getting someone to turn the engine over and see if you can find any leaks or a sucking noise.
    Will it start if you vent the tank by removing the cap ?

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    not likely as it needs a vacume to draw the fuel through to the pump. The other way to do it is to pump compressed air in the filler cap using a compressor and an air gun which forces fuel up the line but it wont resolve the issue of fuel running back to the tank.

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  20. #19
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    Thread revival!

    I have the same problem with my BKD engine.
    When the tank is half empty, after sitting for a few hours or overnight, it takes a few good seconds until it starts.
    The emptier the tank, the more it struggles to start.

    Until now I have changed the battery, the starter motor and the tandem pump. ~A month ago I have also changed oil and all filters, including the fuel one.
    I have siphoned the air from the filter housing and I still have this problem.

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    Anyone?
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    Quote Originally Posted by Johnny Bravo View Post
    Anyone?
    Long story short, Audi spent over £7000 to fix the issue on our car. New Injectors, Cylinder Head, Fuel Pump, EGR valve and it still didn't fix the issue.

    In the end the service manager and technician came to our house to see the issue at hand (it was hard to reproduce otherwise).

    It turned out to be the crank sensor, haven't had the problem since that was replaced but it still does struggle to start occasionally (very random) but now it at least always starts.

  23. #22
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    Mine starts fine when the tank is above half. This is what confuses me.
    It looses pressure on the feed side of the fueling circuit.
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  24. #23
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    Quote Originally Posted by Johnny Bravo View Post
    Mine starts fine when the tank is above half. This is what confuses me.
    It looses pressure on the feed side of the fueling circuit.
    Ours was random, it seemed worse when the tank was less than half full but had it happen a few times with a full tank also.

    Did you get yours sorted?

  25. #24
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    I've changed the in-tank pump last weekend and seems OK now. When I'll have a little time, I'll dismantle the old pump to see what failed.
    I understand that there is a non-return valve somewhere inside,valve which fails.
    I'm curious if it can be changed or fixed somehow.
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