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Struggling to start under low fuel

Squirrelofdoom Jun 1, 2012

  1. Squirrelofdoom

    Squirrelofdoom Member

    Hi guys,

    Thought my car was having an intermittent struggling to start problem, but i've narrowed it down to it only does it when I get below around 1/4 tank of fuel. Basically when it hasn't run in a few hours (overnight mostly) and it's on low fuel, it will splutter when i turn on the ignition and sometimes fail to start entirely. However, if I let the engine turn over a couple times, turn the key off, and then turn the ignition on again straight away it fires no problem. Kinda seems like it struggles to get fuel from the tank to the engine, but once it's "primed" it's fine. Fuel Sender / Fuel Pump issues?

    Also i've been struggling with my boost being really intermittent. Sometimes it will boost fine between 3000 - 4000 rpm, nice and strong, but that's only like once or twice a day really - other than that it feels naturally aspirated. Could this have anything in common with the fault above? My car also spits fuel out the back like nothing else; am checking to see whether that is a dodgy map, but again could be linked?

    Thanks guys,
  2. Dani_B19

    Dani_B19 Audi-sports own special child.

    Mine struggles when under half tank downwards and owt under 1/4 tank it normaly fires on second tun, i think its either down to tired fuel pump or something to do with low fuel pressure in the pipes when the cars been stood, i think the fuel syphons back towards the tank.
    Im just living with it until i fit a new fuel pump.
  3. gen.heinz guderian

    gen.heinz guderian Well-Known Member

    Best to get it scanned with vcds.
  4. Dani_B19

    Dani_B19 Audi-sports own special child.

    Yup, no fault codes.
  5. Rosso TT

    Rosso TT Member

    Definitely fuel pump getting tired or, like in my case a brand new pump faulty.
    The pump is incased in a round canister called swirl pot, the pump itself is dual stage, the first stage fills the canister and the second stage get fed by the canister and pressurize the fuel line, so if there's a condition that the fuel is low in the tank and splashes around it, the fuel line never get starved of fuel due to the canister always filled.
    What i found out is there's a problem in the pump internally and gets the fuel from the canister back into the tank if the fuel level is lower than the height of the canister, this is not a problem because there's plenty of fuel in the canister itself, the fact is that when the level in the canister drops also the fuel in the pump body itself drops so on start up the pump needs to get filled before it pressurize the fuel line so the need for a second crank up.
    Have a look at this.
    Fuel Pump - YouTube
    For the boost problem get it scanned.
    Hope it helps.
  6. Squirrelofdoom

    Squirrelofdoom Member

    Hi guys,
    Very helpful, thanks. Ross, I figured the pump was some kind of self-priming pump (although as you describe it, it isn't strictly a self-priming pump, but kinda works like one). Guess it's not a real problem for now then.

    Had the car scanned and it had a fault from the MAF (Standard...lol); cleaned the MAF but haven't been able to clear and check the codes again to see if it is gone or I want a new MAF. Need to get someone to scan it, but don't want to shell out for a dealer / garage to do it lol

    Cheers guys,
  7. HenryS7377

    HenryS7377 New Member

    tbh i thinks it s general thing with the a3 mines the same, when low on fuel its turns over longer than it normally does to fire..
  8. vrbob

    vrbob Thats no Moon, Thats a space station!

    Any chance its the fuel filter as maybe it gets blocked when low on fuel if its old? I replaced the one on my S3 to find out it was the original filter form the day of manufature thats 10 years and 100k. So for less than a £10 you could try that and even if its not its not a bad thing to do as it should be a service item.
  9. s3dave

    s3dave TFSI Hybrid Supporter

    mine did this and eventually failed,, tired pump..
  10. Chlippo

    Chlippo Member

    My S3 does run lean when low on fuel ( I have an afr gauge) . I have replaced the pump with a known used one and still the same prob.
    I just live with it now till i can get a chance of installing a Walbro pump. OEM are quite expensive here.

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