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boost loss :(

Discussion in 'A3/S3 Forum (8L Chassis)' started by future, Aug 22, 2012.

  1. future

    future Scuderia Vittoria Edition 001

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    hi, i have an apy s3 and latey i have been noticing the boost will drop suddenly from 1.5 to 1 bar when pushing the car. If i lift off the throttle and re apply the boost comes straight back up to 1.5 :s I have checked for boost leaks and vagcom scanned but nothing has come up:think:

    I am leaning towards a weak actuator but could anyone shed some light please?
     
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  3. Greg-S3

    Greg-S3 Active Member

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    Have you had the car smoke tested? It may be a boost leak when under pressure and not visable when at idle and not under load? Also are you running a standard dump valve or has it been changed? I've seen cheap dump valves leak under boost.
     
  4. future

    future Scuderia Vittoria Edition 001

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    i havnt had the car smoke tested yet that was going to be a next move if people think it is worth it? I have got an after market one but it is a 007p that has just been serviced.

    cheers for the reply
    tom
     
  5. Greg-S3

    Greg-S3 Active Member

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    I'd smoke test it first, before I did anything else, as these cars are getting older the vac, boost and breather pipes are becoming brittle, soft, rotten etc and some of them can be hidden away/small etc. I'd personally also try a genuine recirc valve they can handle upto 400bhp if I'm not mistaken and plenty of boost, I know from personal experience I removed a lot of aftermarket valves and fitted standard ones again and it seems to sort numerous boost issues.
     
  6. future

    future Scuderia Vittoria Edition 001

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    sorry i probably should have mentioned i have simplified the pcv system and it is now venting to atmosphere so no leaks from vac points anymore if this helps.

    cheers
     
  7. Greg-S3

    Greg-S3 Active Member

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    I had a mk4 gti turbo come in for boost loss, it turned out to be down to a weak atmospheric dump valve, fitted a standard recirc valve, problem solved! Are you running standard boost levels?
     
  8. future

    future Scuderia Vittoria Edition 001

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    no running a stage 1 remap, requested boost is 1.5 bar iirc. 007p is fitted with a yellow spring same as pretty much everyone else on this forum lol
     
  9. jezzy

    jezzy Member

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    do you have a standard tip?
    could be collapsing under boost
    good excuse for a badger
     
  10. <tuffty/>

    <tuffty/> Badger 5 Edition...Its all about the flow...
    Staff Member Moderator Audi S3

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    Smoke test for sure its a brilliant bit of kit, see this all the time on cars that come in... genuine DV's will generally be ok on tuned engines but stage 2 tunes (22psi ish) would be pushing its reliability and capabilities in staying shut imo... 400hp is a lot of air and a OEM or even a 007p won't really be up to the task of dumping the air for that... ran one before on a car pushing 390hp and there was a little compressor stall on lift off so swapped it for a Forge super size which sorted it...

    Aftermarket valves that give problems tend to be the diaphragm type (APR R1 for example) or the 'atmos' ones (split-r, baileys)... swapping those out with OEM or a decent recirc will always be a better place to be

    <tuffty/>
     
  11. future

    future Scuderia Vittoria Edition 001

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    thank you for the replies :) I will get it smoke tested asap then, would it not leak though still when re applying the throttle at the same revs?

    cheers
     
  12. future

    future Scuderia Vittoria Edition 001

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    sorry to revive this thread, just thought it would be better than starting a new one.

    Had the car boost leak checked and its fine (couldnt find a smoke tester near) but i did some logging with rob on friday and it doesnt look right at all. Can someone please take a look at the logs? and also tell me how to post them lol

    The only thing we did try was swapping my n75(c) with robs newer n75(f) which then gave me peak boost at 0.9-1 bar and gave rob a wee bit more boost, so think this needs changing anyway.

    Car as stands:
    stage 1 CC map
    007p
    silicone tip
    n249 bypass
    pcv delete

    All help much appreciated :)
     
    #11 future, Sep 16, 2012
    Last edited: Sep 16, 2012
  13. future

    future Scuderia Vittoria Edition 001

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    i also tested the car with the n75 electrically disconnected and it held 0.4bar un-till around 5.5/6k rpm when it started to creep up towards 0.6bar-ish if that sheds light on anything?
     
  14. vrbob

    vrbob Thats no Moon, Thats a space station!

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    it is weird this cos am pretty sure Tom does not have any boost leaks as his car runs really well and he has removed most of the #oem crappy pipes etc running a catch can etc.

    The way it boost hard on a third gear run and then at about 5500rpm the boost just drops off and you can hear the turbo spinning and then it stats to build up pressure again and its off.

    To me (and remember i am defo no expert) it feel like the boost is making something like the wastegate open prematurely and loosing pressure till it shuts again and then it can start working again.
     
  15. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Just to add to this if anyone has any ideas Tom also tried my N75 (F version) on his car and it boosted to 1bar and held that we also tried his N75 (C version) on my car and my car requested 1.3bar yet got 1.5bar but it didnt do the drop off of boost like Toms does at higher revs.
     
  16. badger5

    badger5 www.badger5.co.uk
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    boost creep on some k04's is normal
     
  17. JtotheD

    JtotheD Active Member

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    sounds pretty weird tom, is it the same thing that happened when we were out logging the last time i was time?
     
  18. future

    future Scuderia Vittoria Edition 001

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    Thanks for the reply bill, so would boost creep cause the raise in boost when I was on actuator pressure? Or would it cause the over boosting with the n75?

    Yea josh this is that same problem last time we logged and jut can't seem to get to the bottom of it :s when I finish work I will screen shot the logs and see what the experts think
     
  19. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Defo think your N75 is letting your car overboost as it did that on mine too
     
  20. future

    future Scuderia Vittoria Edition 001

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    I think that is definitely a problem and maybe ecu jumping in to soft limp?
     
  21. vrbob

    vrbob Thats no Moon, Thats a space station!

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    Yeah if it's over boosting by 0.2bar I guess it could be sending your ecu into panic mode and therefore pushing it into limp mode
     
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  23. badger5

    badger5 www.badger5.co.uk
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    control should be achieved as std... even with some small creep.. i have seen std cars do this.
    if excessive creep then it will likely overshoot requested boost
     
  24. future

    future Scuderia Vittoria Edition 001

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    thank you for all the replies! i have done screen shots and uploaded them and hopefully we can see the problem
    [​IMG]
    [​IMG]

    looking at them properly now though it seems the ecu is cutting boost :think: could the over boosting be causing this? or am i stabbing in the dark

    thanks for your help
     
  25. badger5

    badger5 www.badger5.co.uk
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    it is pulling back.. timing pull is high also
    no codes?
     
  26. future

    future Scuderia Vittoria Edition 001

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    did think the timing was alarmingly high, but no codes at all and recently replaced maf. The only reason i was saying n75 is because robs n75 on my car made 1 bar of boost and held it which seems like a massive change :s

    thanks for your help bill, much appreciated!
     
  27. vrbob

    vrbob Thats no Moon, Thats a space station!

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    So can that be adjusted using either VCDS or unisettings?

    Or is it a map issue?
     
  28. badger5

    badger5 www.badger5.co.uk
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    could be an n75 thing... if it did'nt used to do it and now does.. map does'nt change, hardware can...
     
  29. future

    future Scuderia Vittoria Edition 001

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    ok well atleast i know what im hunting for now :) im guessing the engine will pull the boost and timing because its out of the safe parameters?
    If i were to reduce the boost in unisettings so i hit 1.3bar would this show if overboosting was at fault? or would the parameters also reduce as i lowered requested boost?

    Only thinking of doing that as a short term safety measure before i can get my hands on a new n75.


    cheers
     
  30. vrbob

    vrbob Thats no Moon, Thats a space station!

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    That was my thinking too as if you can lower boost settings and cure the overboost a bit and stop it hitting whatever its limp mode is then it should hold boost through the rev range. And if your N75 is causing the overboost you can then swap that out and put your settings back up a bit after till its all good in the hood.
     
  31. aragorn

    aragorn "Stick a V8 in it!"
    Staff Member Moderator VCDS Map User

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    lowering it in unisettings will also lower the boost target...
     
  32. future

    future Scuderia Vittoria Edition 001

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    thanks aragorn, guess its time to go on a hunt for a new n75 then!
     
  33. vrbob

    vrbob Thats no Moon, Thats a space station!

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    quite a few on ebay for £40 or less and the F versions too

    second hand one for £28 delivered MK4 GOLF BORA 1.8T TURBO N75 VALVE 058906283F | eBay

    Oh and Tom if you wanna use my VCDS to change your unisettings before you head off to brighton i am about tonight
     
  34. JtotheD

    JtotheD Active Member

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    new n75 then.. after all this! hopefully that will sort it then Tom and then we can get your fmic on if you haven't done it already!
     
  35. Chlippo

    Chlippo Member

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    lets us know how this goes. I have similar prob aprox.
    exept mine have mbc + n75 in parallel.
     

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