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intermittent boost problem

mulli01 Apr 27, 2010

  1. mulli01

    mulli01 Member


    i'm after a bit of advice if anyone can help. I've got a X reg (2000) S3 8L face lift model, had it for about 3 years now and touch wood haven't had too many problems with it.

    It was remapped (custom code) almost a year ago and was fitted with the forge 007 reciric valve at the same time, approx half a year after having the remap my engine management light came on, when i had it hooked up to vagcom i was told the turbo wasn't quite hitting the required boost level and as a result the engine was running slightly rich which is why the light came on. I was told that it could be a sign of the turbo being on it's way out but to try a different N75 valve, i went for the J valve because i'm sure i've read somewhere that the J valve allows the turbo to boost to a slightly higher pressure, after i fitted this the engine management light turned off and was running fine expect every now and then normally on cold mornings i've got very little boost, the more i put my foot down the less power i seem to have and if i slowly release my foot from the accelerator the more i feel the turbo kicking in, almost as if the more i put my foot down it seems to choke/suffercate the engine (most of the time it runs fine but once every couple of weeks or so i get this problem)

    I've again recently had my car hooked up to vagcom (ABS light came on so i thought i'd get it checked out) and these are the faults that came up (apart from the ABS fault code):-

    017705 - turbo throttle valve pressure hose
    017545 - mixture adjustment cylinder bank 1, rich mixture @ idle

    the place where i took it too suggested i look over the breather hoses for spilts which i've done and they don't look too bad (althought they seem very squishy, i don't know if there supposed to be firmer than they are) and also maybe try replacing a temperature sensor.

    I've also had a quick look around for boost leaks but i can't see or hear anything obvious.

    is this all related to my boost problems? and does anyone have any suggestions on what i could try replacing?


  2. Welly

    Welly VX220 SC Driver :)

    Normally indicates a boost leak. Well the ECU is seeing a pressure drop between the turbo and the throttle body basically.

    See this wiki article on Ross Tech web site: http://wiki.ross-tech.com/wiki/index.php/17705/P1297/004759

    This says it could be the N249 valve assembly - which yours should have based on age. May be worth doing the bypass as listed on this thread (http://www.audi-sport.net/vb/showthread.php?84402-N249-Bypass-How-To-(2000-S3-but-same-for-many)) as a test.

    Main culprit is likely to be the DV though. Is easy to test:

    Remove DV.
    Stick index finger in from the bottom and push up on piston or diaphram, and hold open.
    Place other index finger on small top nipple of DV.
    Release holding finger on piston / diaphram.
    Piston / diaphram should HOLD position is seal is good.
    Remove finger from nipple and DV should "snap" shut.

    This fault code brings the following: http://wiki.ross-tech.com/wiki/index.php/17545/P1137/004407

    Get the other problem sorted first - this may go away.
  3. finesse

    finesse Active Member

    Would a duff DV cause boost leak to be intermittent or constant?
  4. Welly

    Welly VX220 SC Driver :)

    I guess it would depend if it was sticking open all the time, or only sticking on occasion.

    If it was sticking, I would take the piston out of it, slap a small amount of molyslip grease around the chamber and reassemble and test.

    It only happens when cold according to the OP, so it could well be that when cold, the metal work is contracted enough to cause a sticking issue. The heat generated by the engine as normal then warms the metal work up, allowing the DV to move more freely.
  5. mulli01

    mulli01 Member

    cheers welly i'll give that a try

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