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  1. #1
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    baffled by a 20vt. engine knock

    its a 2000 agu, drive by wire.

    on the over run you can hear a knock. ive been over the engine with a stethoscope and at first it wasnt clear where the noise came from (not bell housing, not exh. man. turbo area, not the crank case)

    the aux belt tensioner moves with the engine revs and it doesnt move smoothly as ive seen with other engines, it looks jerky

    im planning to get the aux belt off and see how this effects the sound

    anyone experienced the aux belt tensioner creating a knocking (high freq, varies with engine revs) sound before?

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  3. #2
    Welly's Avatar
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    Is the knock definitely coming from the engine itself.

    Just asking as it may be elsewhere and transferring the sound. Engine mount for example.

    Or, as discussed via PM, the chain is possible, but I would of thought that it would do it all the time, as opposed to on overrun.
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  4. #3
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    The only time i have seen tensioner movement was when the lower crank pulley came loose and sheared the key from the back, costing me a head

  5. #4
    6th Gear

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    ill check that too. the aux tensioner wasnt acting like tensioners ive seen before.

    as for the chain, ill get on it with the stethoscope later. ill keep you posted

  6. #5
    RIP S3dave

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    AGU is not drive by wire

    drive by cable normally (DBC)
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  7. #6
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    ive been on it again with the stethescope. the sound isnt "obviously" from the cam chain end.

    as the noise happens on the over run you hear it on gear changes and through the clutch pedal

    the aux belt tensioner does sound particularly rough so ill start with that. the radiator fan eventually came on and the noise was constant (i suppose the revs dropped a touch)

    when the engine starts i noticed revs flick up to 1200rpm, drop to 800rpm very quickly then back up to 1200rpm for the normal idle cycle, so maybe SAI issues too?

    Bill, youre right, its cable (i got the wrong terminology..) its cable, as in old style

  8. #7
    Welly's Avatar
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    Quote Originally Posted by Matt82 View Post

    when the engine starts i noticed revs flick up to 1200rpm, drop to 800rpm very quickly then back up to 1200rpm for the normal idle cycle, so maybe SAI issues too?
    Or a vac leak? Start with the PCV hose from the inlet mani. That ALWAYS splits!
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  9. #8
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    that sort of thing would solve that, but ideally im hunting for that noise. at least these engine bays are easy to work on

  10. #9
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    this weekend i spent some time on the car. new cam chain tensioner and the sump was dropped and the oil pump pick up cleaned.

    the top end is now fine and dandy but there is still a noticable rattle off-throttle.

    now there is nothing coming from the head at all, its all down the gearbox end now. the gearbox mount was taken off to see if that was the cause, same for the dog bone mount

    the last option now is to get the box off and see the state of the dmf. the noise is occurs on a trailing throttle or at idle. it does not vary with clutch position

    if anything it sounds really strong at the gearbox end, but not necessarily at the bell housing

  11. #10
    Welly's Avatar
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    Quote Originally Posted by Matt82 View Post
    this weekend i spent some time on the car. new cam chain tensioner and the sump was dropped and the oil pump pick up cleaned.

    the top end is now fine and dandy but there is still a noticable rattle off-throttle.

    now there is nothing coming from the head at all, its all down the gearbox end now. the gearbox mount was taken off to see if that was the cause, same for the dog bone mount

    the last option now is to get the box off and see the state of the dmf. the noise is occurs on a trailing throttle or at idle. it does not vary with clutch position

    if anything it sounds really strong at the gearbox end, but not necessarily at the bell housing
    Hmmmm, dodgy dual mass?

    But as you said not at the bell housing, it may not be.
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