1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

baffled by a 20vt. engine knock

Discussion in 'A3/S3 Forum (8L Chassis)' started by Matt82, Apr 22, 2010.

  1. Matt82
    Offline

    Matt82 Active Member

    Joined:
    Sep 7, 2009
    Messages:
    2,366
    Likes Received:
    2
    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?
    #1
  2. Welly
    Offline

    Welly VX220 SC Driver :)

    Joined:
    Aug 5, 2009
    Messages:
    10,699
    Likes Received:
    117
    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.
    #2
  3. Broken Byzan
    Offline

    Broken Byzan Photographic Moderator Staff Member Moderator

    Joined:
    Apr 26, 2004
    Messages:
    12,578
    Likes Received:
    270
    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
    #3
  4. Matt82
    Offline

    Matt82 Active Member

    Joined:
    Sep 7, 2009
    Messages:
    2,366
    Likes Received:
    2
    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
    #4
  5. badger5
    Offline

    badger5 RIP S3dave Site Sponsor

    Joined:
    May 28, 2004
    Messages:
    7,269
    Likes Received:
    670
    AGU is not drive by wire

    drive by cable normally (DBC)
    #5
  6. Matt82
    Offline

    Matt82 Active Member

    Joined:
    Sep 7, 2009
    Messages:
    2,366
    Likes Received:
    2
    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
    #6
  7. Welly
    Offline

    Welly VX220 SC Driver :)

    Joined:
    Aug 5, 2009
    Messages:
    10,699
    Likes Received:
    117
    Or a vac leak? Start with the PCV hose from the inlet mani. That ALWAYS splits!
    #7
  8. Matt82
    Offline

    Matt82 Active Member

    Joined:
    Sep 7, 2009
    Messages:
    2,366
    Likes Received:
    2
    that sort of thing would solve that, but ideally im hunting for that noise. at least these engine bays are easy to work on
    #8
  9. Matt82
    Offline

    Matt82 Active Member

    Joined:
    Sep 7, 2009
    Messages:
    2,366
    Likes Received:
    2
    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
    #9
  10. Welly
    Offline

    Welly VX220 SC Driver :)

    Joined:
    Aug 5, 2009
    Messages:
    10,699
    Likes Received:
    117
    Hmmmm, dodgy dual mass?

    But as you said not at the bell housing, it may not be.
    #10

Share This Page