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Fuelling issue..

Discussion in 'A4/S4 forum(B5 Chassis)' started by Lee Goodall, Oct 9, 2008.

  1. Lee Goodall
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    Lee Goodall ..got my head together!

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    [Oct 9, 2008]
    I'm only getting 23mpg at the mo.. most is town driving though but I'm also getting a smell of fuel from the exhaust. I'm going to try VAG.COM at the weekend but using my hand held scanner I can see that there are no fault codes.

    I have fitted.. new coolant temp sensor, new thermostat, new maf sensor, new lambda sensor and cleaned the throttle body all as part of my engine revamp.

    If anyone has any suggestions I'd appreciate it.
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  3. Blue_Thunder
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    Blue_Thunder Active Member

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    [Oct 9, 2008]
    Faulty EGT sensor? If it's telling the ECU that it's running too hot (even though it might not be) then the ECU will chuck more fuel in to keep EGT's down.
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  4. Lee Goodall
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    Lee Goodall ..got my head together!

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    [Oct 9, 2008]
    It's an AEB engine (1.8T) so I've only got the Lambda sensor to measure the exhaust gases haven't I??
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  5. Blue_Thunder
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    Blue_Thunder Active Member

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    [Oct 9, 2008]
    Lambda only measures unburnt oxygen in exhaust gasses, not exhaust gas temperatures. Not sure if the 1.8T has one, but i'd be surprised if it didn't.

    Saying that, a faulty EGT would throw a fault code.
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  6. Izzy1
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    Izzy1 Vorsprung Durch Technik

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    [Oct 9, 2008]
    check to see if you have the MAF sensor the right way round.

    had this problem on my Bora not so long ago.
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  7. Lee Goodall
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    Lee Goodall ..got my head together!

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    [Oct 9, 2008]
    Yeah the MAF sensor is the right way round.. only had it out the other day.
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  8. Lee Goodall
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    Lee Goodall ..got my head together!

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    [Oct 9, 2008]
    As far as I'm aware there's only the Lambda sensor bolted into the exhaust/cat just after the exhaust manifold which like you say only measures the mixture after ignition.. although you do get an intake air temp sensor so you'd think there would be an exhaust gas sensor too? Anyone??
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  9. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Oct 9, 2008]
    1.8t doesnt have EGT sensor

    My 1.8t was returning similar economy when we baught it due to a knackered thermostat, but it was very obvious as the guage never reached the middle!

    Its worth mentioning that while our car returns a healthy 30mpg atm, it also has a fuel smell from the exhaust, mainly because the cat is dead, the only reason modern cars dont smell of fuel is the cat burns off any remaining hydrocarbons, remove the cat and it smells pretty similar to any older EFI car.

    Because of this i suspect the cat may well be toast on your car although taht doesnt explain the fuel economy... and you've already replaced the usual culprits. I would get the car on a gas analyser and see whats coming out the tailpipe

    if its circa 0.5-0.7% CO then i suspect the cats dead and the engine is otherwise running fine. If its >1% CO the cats also likely dead, and theres something else up with the management!

    I imagine that if your driving consists largely town only, ie 30-40mph and constant start-stop, plus a lot of the time being short journeys (in cold start mode, using more fuel) they economy figures are probably fine.
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  10. Lee Goodall
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    Lee Goodall ..got my head together!

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    [Oct 10, 2008]
    Cheers aragorn I was going to go down the route of the cat as the car seems to be running well and if anything was seriously wrong before the cat I would hopefully be seeing a fault code.

    I'll try to get to the garage to get the exhaust gas analysed.
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