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Thread: 2009 R32 - high fuel trim on bank 1

  1. #11
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    Quote Originally Posted by Danners74 View Post
    Is the exhaust leak free a the flexi joints? What fuel are you using?
    DIY here, thought:
    Your vehicle is 173KM or 108K miles. I'm assuming the motor mounts are worn or have been replaced? Or you just stomp on it alot?
    Letting them go too long? Maybe damaged flexi-joints? Or maybe they were replaced and but one of the flexi-joints got buggered during installation?
    At idle, the flexi-joints (or some other item) is fine. Mid to higher RPM, motor starts moving around due to marginal mounts and then something starts leaking, maybe the flexi-joints?
    Air is added pre-Cat via cracked flexi (or other), and frt O2 sensor sends lean condition info to ECU thus added fuel due to fake lean condition. One flexi joint is good, the other bad?
    Explains normal op @ idle. Your parts cannon might be out of ammo.....?
    Last edited by Dunwood; 11-10-2019 at 08:06 PM.

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  3. #12
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    Quote Originally Posted by Dunwood View Post
    DIY here, thought:
    Your vehicle is 173KM or 108K miles. I'm assuming the motor mounts are worn or have been replaced? Or you just stomp on it alot?
    Letting them go too long? Maybe damaged flexi-joints? Or maybe they were replaced and but one of the flexi-joints got buggered during installation?
    At idle, the flexi-joints (or some other item) is fine. Mid to higher RPM, motor starts moving around due to marginal mounts and then something starts leaking, maybe the flexi-joints?
    Air is added pre-Cat via cracked flexi (or other), and frt O2 sensor sends lean condition info to ECU thus added fuel due to fake lean condition. One flexi joint is good, the other bad?
    Explains normal op @ idle. Your parts cannon might be out of ammo.....?
    Thanks for the reply. Yes, I agree that's possible. Engine mounts have all been done reasonably recently.

    Re: parts cannon - they weren't all done for the fuel trim! I was just trying to give some recent history for the vehicle

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  5. #13
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    I decided to revisit old ground today.

    Simultaneously capped off, at the intake manifold:
    • Exhaust flapper
    • EVAP
    • Intake changeover
    • Brake booster
    • Noise pipe / resonator

    And there was no change on the fuel trims which suggests the vacuum system is fine. That makes sense to me, because the issue is a partial fuel trim (not idle), and it is only affecting one bank.

    Which doesn't really get me much further. Still need to look for exhaust leaks giving a false lean, or something along the lines of a bad injector.

  6. #14
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    Spark Plug analysis would show this too no?
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    Quote Originally Posted by Jack@European_Parts View Post
    Spark Plug analysis would show this too no?
    There was nothing untowards to my (untrained) eye when I pulled them. A touch rich across the board would be my assessment... will take another look when I get the chance.

    Thinking about the flexi pipes leaking underload, I remembered why I initially discounted that - the flexi pipes are downstream of the precat sensors, so I don't think a leak there would be able to introduce a false lean?

  9. #16
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    Quote Originally Posted by cas View Post
    Thinking about the flexi pipes leaking underload, I remembered why I initially discounted that - the flexi pipes are downstream of the precat sensors, so I don't think a leak there would be able to introduce a false lean?
    Very good to question it; but because of the pulsed nature of exhaust gasses, combined with the high and low frequency/speed pressure waves, negative pressures (relative to atmospheric) are indeed created in the system. These can 'suck' oxygen-rich fresh air in and up to the sensor.

  10. #17
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    I know you are not agreeing with flex pipe leaking. Been there!

    Read this on a R32 flex pipe causing problems with 02 signal.

    https://forums.ross-tech.com/showthr...inking-bad-ECU

    Good Luck

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  12. #18
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    Quote Originally Posted by Zenerdiode View Post
    Very good to question it; but because of the pulsed nature of exhaust gasses, combined with the high and low frequency/speed pressure waves, negative pressures (relative to atmospheric) are indeed created in the system. These can 'suck' oxygen-rich fresh air in and up to the sensor.
    Thank you for that, very informative. I never thought of it that way, but it makes sense

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    Quote Originally Posted by vwtech View Post
    I know you are not agreeing with flex pipe leaking. Been there!

    Read this on a R32 flex pipe causing problems with 02 signal.

    https://forums.ross-tech.com/showthr...inking-bad-ECU

    Good Luck
    Just read through your thread. It is certainly making me lean (pardon the pun) that way. Particularly as I very recently noticed 033 trims zero'ing out like you mention in your OP.

    The flex pipes look a little easier to get to on the MkV than you describe about the MkIV. I'm guessing my MkV options are (1) drop the downpipes and cut out/replace the flex pipes, or (2) replace the entire downpipes and cats.

    Is that about the measure of it? If so, I'll need to weigh up the chances of a good repair versus splashing out on some aftermarket downpipes with high flow cats.

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  15. #20
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    Quote Originally Posted by cas View Post
    Is that about the measure of it?
    If that's a question I don't understand?

    Does MKV have SAI with a Kombi valve you can hold open while jumping SAI pump? Then block tail pipes and feel around flex joints?
    If O2 zero out then I say same problem. Glad it's got you thinking about flex pipes. Kicked my A$$ for sure figuring it out.
    The cats were separate from the down pipe with flex joints on MKIV so I got the whole dealer down pipe no cats.
    If cats are part of pipe with flex joints I would think about welding new flex joints? Just get a real good type!!!! That's easier said then done...

    Good Luck

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