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Loss of boost in 5th 6th only

Discussion in 'A3/S3 Forum (8L Chassis)' started by scotty_24, Sep 7, 2013.

  1. scotty_24
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    scotty_24 Member

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    [Sep 7, 2013]
    Car Is a revo stage 1 amk S3.
    The car is boosting fine to 1.5 bar and holding 1.2 bar in every gear up to 5th.

    In 5th and 6th it's boosting to 1.5 bar but rapidly dropping off to .08, you can also feel the loss of power.
    I've done logs and I'm getting extremley high CF in all cylinders high up the rev range, I'm hitting CF of 11 on some runs.
    Does anyone have any ideas?
    The car is ran on Vpower all the time, I only ever use 95 Ron if I get caught out, and all it will get is £10 worth to get me to the next shell.
    I've not done / changed anything in the last few weeks.
    2 months ago all the pipes under the inlet mani were changed / forged and it's since ram a healthy 262.4 bhp on the rollers maybe 7-8 weeks ago.
    Tha is for any help or ideas.
    m

    Scotty
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  3. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Sep 7, 2013]
    check your throttle body pipe... undo it and look for oil pouring out of your throttle body if cf's are that high...
    #2
  4. scotty_24
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    scotty_24 Member

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    [Sep 7, 2013]
    I had the offside front boost pipe off the other night to fit the forge c shaped hose that fits on the side of the inlet manifold. The inside of the pipe was bone dry just about.
    on the log block 002 you could see the g/s reading plumet from approx 200 gs to approx 150.
    Now the other night I unplugged the maf and the car driver fairly similar to normal, if not it felt a bit quicker.
    Usually when I log I get max gs readings of around 217 max which indicated good Bager assisted airflow? Ha ha
    Help
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  5. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Sep 8, 2013]
    question is why the high cf
    when i see this there is oil pouring out of the throttle body

    tired maf would cause initial underfueling and underscale, so it could also be that, and its running on lower loads (thinks so anyhows) which would run too much timing...

    maf worth a punt.
    high cf will cause it to drop boost......... self preservation mode
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  6. scotty_24
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    scotty_24 Member

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    [Sep 8, 2013]
    Il whip off the throttle body hose and have a look.
    what would cause oil in the pipes?
    as I say all the PVC system hoses are new .
    Yeah so the high c/f is backing off boost to save the engine. This is not good :(
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  7. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    [Sep 8, 2013]
    oil sources are pcv and turbo
    #6
  8. scotty_24
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    scotty_24 Member

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    [Sep 8, 2013]
    Ok, thanks for your help bill !
    only other thing I can think of is that I replaced the vac lines to the DV and FPR, and cable tied them under the inlet mani.
    if the one for the fpr is loose maybe that could cause the problem?
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  9. badger5
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    [Sep 9, 2013]
    checked the throttle body pipe yet??
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  10. scotty_24
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    scotty_24 Member

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    [Sep 9, 2013]
    I have, heres some pictures Bill let me know what you think.
    [​IMG]
    [​IMG][​IMG]
    [​IMG]
    #9
  11. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 9, 2013]
    You could try temporarily feeding the PCV into a coke bottle or similar and having a drive to see if the problem goes away and/or the coke bottle fills up with oil.

    Some logs showing the MAF readings, intake temps and EGT's as well might be useful.
    #10
  12. badger5
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    [Sep 9, 2013]
    clean it off, go give it some beans, remove it again and recheck.. see if the oils pouring out again.
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  13. scotty_24
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    scotty_24 Member

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    [Sep 12, 2013]
    Big problems. Oil in the pipes again Same as photos above.
    Its now shooting up to about 1.8 bar then rapidly dropping off to about .08 bar.
    What on earth is going on?
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  14. badger5
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    [Sep 12, 2013]
    boost issue is likely seperate to oil injestion issue.
    if pcv is venting to atmos your oil is either all sat in intercooler and being picked and blown thru under boost, or hosing out of the turbo.. check turbo charge pipe before 1st intercooler. remove clean it drive it and recheck etc... n75 electrically off if i were you at this point
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  15. scotty_24
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    scotty_24 Member

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    [Sep 12, 2013]
    The PVC system is running standard set up just new pipes all round.
    ive unplugged the n75 and the car drives ok but obviously only boosts to approx .5 bar.
    ive cleaned the pipes again.
    So I leave the n75 unplugged and drive it?
    Many thanks for your help Bill
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  16. badger5
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    [Sep 13, 2013]
    if the oil has pooled in the charge pipework from previous pcv split pipes, it will get scooped up when airflow rises..
    if on std twin smic, i would be removing them at this point and emptying their oil out, cleaning them and refitting... and as a temp measure to gauge is it legacy oil goop or active heavy breathing pcv, remove the return to tip into a catch can to see how much hoses out.... IF you still get copious amounts of oil coming thru to the throttle body after the pipes have been cleaned and breather is seperated into a catch can, the oil source would point to the turbo which would be confirmed by looking at the main charge pipe oiling up rapidly after clean.

    good luck
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  17. scotty_24
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    scotty_24 Member

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    [Sep 13, 2013]
    I've been having a think on this, and this all stems from when I topped the oil over maximum by mistake.
    could this skimpily be a case of the oil breather system doing its job and desperately trying to get rid of the excess oil!
    Tonight I have cleaned out the boost pipes.
    the amount of oil that came out of the lower boost pipes and intercoolers was unbelievable !

    Ive ran the PVC pipe that usually goes into the tip (from the bottom of the hokey puck) into a coke bottle.
    i will monitor how much it's chucking out and report back.
    now just to find something to block the hole left in the TIP to ensure nothing gets sucked through!

    many thanks for your help on this, I shall report back!
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  18. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 14, 2013]
    Have you fixed the oil level, or are you still driving around with it overfilled?

    What i dont understand is how you can get 0.08bar of boost. Actuator pressure is 0.4 or thereabouts, the ECU would have to have both dialled out all the boost, and half shut the throttle plate, or opened the N249, to get it down to 0.08bar.

    If your rerouting it into a catch can (bottle) you cant just do the TIP end. There should be two connections, one to the tip and one to the inlet manifold. If you have the tip end open and the other end connected to the manifold you create a nice big Mass Air leak when off boost.
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  19. scotty_24
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    scotty_24 Member

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    [Sep 14, 2013]

    Ahhh sorry its meant to say .8 bar, type error my mistake.
    Ive sorted the oil level its now ok.

    hmm ok so i need to block off the tip and the plastic pipe that leads down to the PCV valve? Im confused now
    #18
  20. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 14, 2013]
    No.

    The PCV has two branches. Off boost, the inlet manifold vacuum sucks the PCV fumes streight into the inlet manifold. Once on boost, a check valve closes and the fumes are redirected to the TIP.

    However if you connect the catch can to the TIP connection, and leave the rest of the pipework stock, then when NOT on boost, the inlet manifold can draw air in thru the open catch can, bypassing the maf and messing up the fuelling.

    I'm not entirely familiar with the S3 PCV layout, but if you want to divert to a catch can, you'll need to remove the inlet connection as well. I'm not sure if you can just blank the inlet side, and leave the TIP end going to a catch can. That would certainly work OK on the A4. You'll need to look at the pipework layout to see if thats possible on the S3.
    #19
  21. JUS3IN
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    JUS3IN silver sleeper

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    [Sep 14, 2013]
    i had oil in my pipes after just slightly overfilling with oil. stick a bolt in the tip and clamp it down mate yes.
    #20
  22. scotty_24
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    scotty_24 Member

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    [Sep 16, 2013]
    Quick update!
    On friday night I cleaned out all of the boost pipes and drained the intercoolers.
    There was quite a bit of oil in the o/d/f intercooler, not so bad in the n/s/f.
    Ive also done the N249 bypass at the same time.
    Last night I took it out for a good run using various style of acceleration eg orogressive and harsh, and Im pleased to say it boost absoloutley fine!
    Its boosting to 1.5 bar and holding 1.2 to red line in all gears :)

    My plan is to fit a cheap ebay catch can and monitor the situation that way, as well as periodically checking the boost pipes for oil.

    Do people generally vent to the TIP or to atmosphere?

    Can I say thank you to Bill and anyone alse that has helped me, and I will report back with any more findings!
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  23. scotty_24
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    [Sep 29, 2013]
    Well it's been a few weeks and the catch can is fitted.
    There is still some oil getting to the throttle body. I don't know of this is The remain emits of the oil still in the system, what else can it be?
    its still intermittently boosting up to 2 bar and rapidly dropping off to .8 bar.
    this happens under harsh acceleration. Under progressive acceleration it's ok.
    Anyone have any ideas?
    #22
  24. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    [Sep 29, 2013]
    If its boosting to 2bar then you have other issues mate... this is why its dropping to 0.8bar as its seeing more boost than it has requested... can you swap the N75 out with one from a mates car maybe? would say just by a new one but they are 50ish quid and would prefer to see logs of N75 duty, boost request/actual before saying for definite..

    <tuffty/>
    #23
  25. badger5
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    [Sep 29, 2013]
    did you clean out your intercooler pipes and intercoolers? if not pooled oil will still get blown thru..
    need to be emptied and cleaned
    #24
  26. scotty_24
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    [Sep 29, 2013]
    I just drained the intercoolers by removing the connecting pipes and draining the oil that way.
    Ive just bought a front mount intercooler kit which I'm fitting next weekend so that will eradicate any oil in the system.
    i think I may just buy a N75 as piece of mind that's its new, the Maf is 3 years old but isn't showing signs of giving up or playing up.

    Thanks again in advance for any help
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  27. scotty_24
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    [Oct 1, 2013]
    Bump
    any ideas what could be causing the massive over boost? N75?
    #26
  28. JUS3IN
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    JUS3IN silver sleeper

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    [Oct 1, 2013]
    most likely n75 or n75 pipework/actuator/turbo if you plumb the charge pipe straight to the actuator eliminating the n75 (the ecu's boost control) it should run 5/6psi actuator pressure i believe, if you are seeing more the issue is mechanical most likely actuator or turbo. you can test the actuator by cutting a tyre valve up and clamping it into your actuator pipe then pumping it up to 30psi and see if it holds..
    #27
  29. scotty_24
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    scotty_24 Member

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    [Oct 2, 2013]
    Ive unplugged the N75 and it runs actuator pressure ok, it doesnt boost more than 5/6 psi (it was .4/.5 bar as far as I remember).
    Im going to take a punt at it being the N75, Il get that done and report back and let you know when I get on.

    Intercooler fitting tonight, that will erradicate any oil in the boost system :)
    #28
  30. crispynz1
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    crispynz1 Member

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    [Oct 21, 2013]
    Any update on this Scotty? Going through similar problems myself. Cheers.
    #29
  31. scotty_24
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    scotty_24 Member

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    [Oct 21, 2013]
    Ive fitted a oil catch tank and deleted the PVC system to erradicate oil in the pipes.
    Ive also fitted a front mount intercooler. There is not a drop of oil in the boost system now, they have been fitted about a fortnight to three weeks.
    I replaced the n75 and bingo, no more overboost. TPS gave me an "E" valve, its a supercession to the "f" valve :)

    Cars running like a dream now, and its ready for stage 2 next month :)
    #30

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