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Turbo pressure noise under acceleration - help me tell dealer what to look for!

Discussion in 'A3/S3 Forum (8L Chassis)' started by chiefb, Dec 21, 2007.

  1. chiefb
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    chiefb New Member

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    Hello all,

    I've just received my 2002 S3 (225bhp) back from the body repair shop. It needed a new passenger side front wing and headling after a dustcart decided to scrape it down one side whilst it was parked...

    Anyway - the car is now making a new noise. It can only be heard when accelerating and working the turbo, and initially sounds like a raspy noise coming from quite low down behind the passenger footwell or glovebox.

    If you then release the accelerator, you get a whoosh / fizz noise, like the pressure is being dumped.

    I had initially suspected the Diverter Valve problem as documented here:
    --- sorry can't post url's yet --- thread number: 19986

    but having taken it to local mechanic and then Audi dealership, they don't reckon it is this, given where the noise seems to originate from (although I don't think they've done any proper diagnosis).

    I'd appreciate any input you may have for me, so I can re-brief a mechanic for what to look for. So far I have:

    - check for split pipes on/around intercooler
    - check intercooler itself (I've heard of cases where seals can crack?)
    - exhaust manifold/gasket from turbo

    What else am I missing?

    I'm obviously suspicious that something was damaged during the recent repair work, but until I find the cause it's difficult to prove. This post looked promising baring in mind I had the wing changed, but it would seem that this isn't something that could affect a standard un-modded car ?

    --- sorry can't post url's yet --- thread number: 12243

    sorry for the essay! and thanks in advance
    #1
  2. audi-tech
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    audi-tech New Member

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    Theirs an orange pipe behind the turbo that sometimes spits.. but that would not relate to the area you are hearing it from.. Have you checked both intercollers?
    #2
  3. S POT
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    S POT Member

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    Mine has always given a whoosh / fizz noise as you have discribed when you let off the throttle or on gearchanges? Is this not normal with S3`s then?
    #3
  4. chiefb
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    chiefb New Member

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    Not to the extent that I'm now hearing, and it's noticable when the turbo is spinning up as well - almost like a raspy exhaust note..

    I'm going to be vigorously checking all the pipes to and from each intercooler over xmas, so I'll let you know how I go..
    #4
  5. james_S3
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    james_S3 New Member

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    i have exactly the same problem with my S3. Its standard apart from forge DV. I have posted a thread but didnt have many suggestions apart from take it to a garage!!!! I have checked everything now (i think!!) and its driving me crazy!!! also seems like its lost power :sadlike:

    really does sound like its coming from around the air box area. Does anyone know if the N249 valve that controls the DV could be dumping the boost back into the TIP? Although the car does peak at 0.8bar and does not drop off!
    #5
  6. chiefb
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    chiefb New Member

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    Well - it's definately not the DV. Mine was changed today and noise is still there.

    Going to get the garage to replace the intercooler pipes and clips next. Really hoping I haven't got a puncture in the intercooler!
    #6
  7. simch
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    simch Active Member

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    What does vagcom say?
    #7
  8. jamieface
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    jamieface the only S3 in the villiage

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    this all aounds very familliar. my car 2001 S3 is doing the same and it seems like it lost power ?? is the noise like a sucking air kinda sound ??? or a whooshing noise from behind the glove box ?? not a good description i know but hey !!!
    #8
  9. chiefb
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    chiefb New Member

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    Yep that is exactly it.

    It's tricky to describe - as without hearing it, most people just think it is the normal operation of the turbo - but I know different because I've owned the car from new - and the noise has only appeared after the recent repairs to front wing..
    #9
  10. S POT
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    S POT Member

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    So should there be no noise when the throttle is released or on gearchanges? Have'nt had my car long and it has always made a loud whoosing sound when changing gears etc. My mum had a 2003 S3 and cant remember hers making any noise :blink: Feels a bit flat aswell!
    #10
  11. madvw
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    madvw Active Member

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    as simch says, you're going to need a fully registered version of vag-com to get to the bottom of this one. You need to log requested Vs. actual boost to see if you have a boost leak.

    Seems a bit fishy though that you had an accident in the location where there's a SMIC, and now you have weird noises when boosting.
    #11
  12. JB_A3_Turbo
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    JB_A3_Turbo Member

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    I've had this kind of noise on my 1.8T. DV was replaced but no different. Had it remapped a year ago with revo and replaced the DV with a forge eliminator valve. Noise is still there though. I'm fairly sure that this is normal-someone on here explained comprehensively ages ago. My car doesn't feel under powered at all, nice and responsive (probably 185-190bhp) and is as fast as I'd expect it to be for the power..
    #12
  13. Backdraft Motorsport
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    Backdraft Motorsport 1.8T & 2.0TFSi Specialists Site Sponsor

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    Dont waist time and money fiddling around without doing a pressure check. If you are in the Milton Keynes area, pop in and we will do a pressure test for you. Otherwise ask a good local independant to carry out a test for you. It's the most cost effective way of locating your problem.
    Best Regards
    Mark
    Backdraft Motorsport
    01908 821216
    #13
  14. james_S3
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    james_S3 New Member

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    i have pressure checked the whole system from the turbo to the inlet manifold!!! Still no luck. And i have got 0.8bar of boost which does not drop off. Really does feel underpowered.

    Just a thought but could the n245 valve (which regulates the vacume to the DV) on top of the rocker cover be at fault causing the DV valve to leak pressure into the TIP? But then sureley my boost would drop??
    #14
  15. danotto
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    danotto VAG HUNTER

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    i know this sounds daft but are you sure that the turbo inyake pipe isnt split anywhere allowing air to be sucked into the pipe from the engine bay rather than just the air filter?

    Mine also has a slight whoosh but im sure its normal.
    #15
  16. natedogg1983
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    natedogg1983 New Member

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    s3 2001. just got the car and few days after driving it for about a week i have got a new noise. you cant hear it when driving steady, but when you give it some you can hear the turbo spooling up, then a louder noise when it really goes. It isnt the standard noise because it didnt use to sound like that.
    it still goes ok but dont think its right. couldnt keep up with civic type-r today..... not what i wanted .

    worried.
    #16
  17. ianysm
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    ianysm Active Member

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    Definately sounds like a leaking pipe somewhere. I'd check around the area they repaired. Hope its not a faulty intercooler, but could be damaged in the accident?
    #17
  18. Biggied
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    Biggied They called him mellow yellow.

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    If its only happened since the wing repair I'd have the cold air feed that pokes through the n/s/f inner wing looked at, its an oval shape pipe that feeds into the end of the airbox. When this isn't sitting right it can make a slight sucking noise as you've described or a deeper induction noise (like an cone filter/modded airbox). The afore mentioned recirculating valve releases its pressure into the intake pipe so the more intake/induction noise you can hear the more valve noise you hear, this would explain the noises during accelaraiton and when lifting off.

    An incorrecty fitted/sealed air box top section can cause the same noises also.

    If it isn't infact a boost leak you have this is the area I'd be looking at!!

    Cheers Ewan.
    #18
  19. natedogg1983
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    natedogg1983 New Member

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    put boost gauge on today. to check things out..
    it peaks at about 19psi around 4000 rpm. after that it dies off, and by 6000rpm only getting 10psi. is this usual for am 210bhp S3.
    #19
  20. subby
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    subby Member

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    hm...

    Ive got this, but i know why lol. It got noticable when i put a pipercross panel filter in, and even more so now with a cone. I always thought it was normal, someone on here explained it was normal a while back i think.

    mine only does it under low boost, on full throttle/full boost it goes away and off i go :ninja:
    Last edited: Dec 8, 2009
    #20
  21. S3KO4
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    S3KO4 Member

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    19psi from a 210 with no map is a bit optimistic. unless it has been mapped before you. it is normal for boost to tail off but not sure on the standard map!
    #21
  22. natedogg1983
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    natedogg1983 New Member

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    i think it might be my dump valve?? can you bypass it somehow
    #22
  23. Welly
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    Welly VX220 SC Driver :)

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    No you can't bypass the dump valve, it is there for an extremely specific reason! I'll explain below.

    A possibility, but unlikely. You would experience boost drop since the whole point of the N249 valve is to regulate boost. It will be used if the MAP sensor tell the ECU there is more boost than requested, and is also used to limit power if the traction control deems it necessary. Lots of info about the N249 and vac chamber on this post: http://www.audi-sport.net/vb/showthread.php?t=84344

    If you believe this to be the problem, you can bypass it. This is the link to my 'How To' thread: http://www.audi-sport.net/vb/showthread.php?t=84402

    What you all seem to be lacking here is knowledge of the point of the Dump/Dirverter valve on an Audi 1.8T engine. The Forge 007p and standard Audi DV are both DIRVERTER valves.

    DV Theory: When you let your foot off the throttle (and the throttle body's butterfly closes) the air being pumped out of the turbo at pressure suddenly has nowhere to go.

    Without a dump valve, this air would start pressurise the pipework and eventually prevent the turbo spinning (called compressor surge or turbine stall).

    An atmospheric dump valve vents this air into the atmosphere (obviously), making an audible Ptush noise (think Subaru!).

    Our 1.8T engines have a diverter valve. Similar principle, however the air doesn't get released, it gets put back into the inbound air flow to the turbo. This rush of pressuried air helps prevent turbo lag when changing to the next gear. However, not all of it gets recycled through the system, especially if changing gear slowly. In this case, some of the air goes back out through the air filter (since the DV only puts the air in not much after it). This is the noise you will be hearing when changing gear and/or letting off the throttle.

    A cone filter, or incorrectly closed/cold air feed pipe removed air box will make this noise MUCH more audible as the air escapes out of the filter.

    It will be louder if you change gear when the turbo is at full spool, quieter if you are only doing 1500 rpm. Obviously the more the turbo is working, the more air moved, more pressure, bigger release noise. If tanning it/at full boost, you will be changing gear quicker (normally) and more air will be reused.

    Have a look here for more info http://en.wikipedia.org/wiki/Blowoff_valve

    This is absolutly spot on, and exactly where I would start.

    Sorry for the long post - but hopefully it'll be useful. :)
    #23
  24. Welly
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    Welly VX220 SC Driver :)

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    Expect the standard map to drop the boost off. If you want a bit more, might be worth thinking about a different N75 valve (more specifically the N75J). Can cause limp mode due to overboost in some S3s, its a bit hit and miss. But if you want to get a bit more boost/better performance for £50 from Audi, it's worth a punt IMO. I've got one :).
    #24
  25. Welly
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    Welly VX220 SC Driver :)

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    Who's to say that Civic Type R wasn't messed about with? They're somwhere handy to 200 BHP standard, with no 4WD mechanical lag and lighter than an S3 in the first place....
    #25
  26. MIKE GTR
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    MIKE GTR Member

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    ^^^^ the 3 most sensible and understated posts that i've so far read on here
    #26
  27. natedogg1983
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    natedogg1983 New Member

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    put standard one on but still noise.

    diy pressure test next
    #27
  28. S3 Paul
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    S3 Paul Moderator Moderator

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    Had this same problem today...
    It was the 2 pipes that come off the hard top boost pipe ... one goes to the DV one goes the the N75 valve...
    Where they come off the boost pipe they take a sharp turn... check they arent split. mine was and by christ was the turbo loud !
    They are not too cheap from audi... mine are now silicone... should work well.
    Hope my finding help you too.
    #28
  29. The Doctor
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    The Doctor Active Member

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    Some really informative stuff in this thread, especially from Welly.

    Reading all this has got me thinking about my 2003 S3, which I bought in July this year. It has a stage 1 remap from APS in Brackley & a Forge 007P fitted. Air filter is standard.

    It's the 1st turbo car I've owned, so I'm not familiar with a lot of the technical stuff but...

    When I am accelerating I can hear & feel the turbo spooling up. After around 4k rpm when accelerating I start to get a different noise that is almost like sucking the last bit of a frothy milkshake up through a straw (know what I mean?). Acceleration still pulls well with no ovious issues. Is this noise OK?

    The car's done this since I bought it & I've had it Vagcom'd with no issues.
    #29
  30. Welly
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    Welly VX220 SC Driver :)

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    Yeah, if it's always done it with no side effects then I'm sure it's fine. All cars make different noises depending on the hardware that's attached to it.

    Its really difficult to describe noises, I well know, but at 4K your turbo will be at full spool flowing a little under 200 grams per second of air. That's a lot of air! I expect the noise you describe is the turbo pulling it through the air box/filter.
    #30

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