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S3 only boosting to 10 PSI

Discussion in 'A3/S3 Forum (8L Chassis)' started by blued, Feb 4, 2013.

  1. blued
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    blued Member

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    I had a problem with my S3 at the end of last year, intermittently it would go into soft limp mode and only boost to 4 PSI, it got worse and worse until the times it did boost it wouldn't hold at all. At the weekend I replaced the N75 valve - the old one fell apart when I removed it so it was definitely the problem. Now the car holds boost but only boosts to 10 PSI. When I bought the car it would boost to at least 15 PSI. I can't remember the exact figure as it was that long ago I started having problems, but it was boosting to 15 PSI while I was having the intermittent issues with it.

    The car is a 1999 210bhp model and the previous owner said he had a 240bhp map done. What is standard boost on this model? 12 PSI?

    Has anyone had similar problems?
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  2. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    Standard is 11/12 psi on these. Have you scannes for vault codes? Could be possible boost leak.
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  3. blued
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    blued Member

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    I was getting the following, which was caused by the N75 being faulty and leaking

    17963 - Charge Pressure: Maximum Limit Exceeded
    P1555 - 35-10 - - - Intermittent

    I'll have it cleared and check again. The boost holds so I don't believe there is a leak? It definitely boosted to over 15 PSI when I first got it. The car was much faster before I started having these issues...
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  4. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    boost holding proves nothing dude.
    are you able to get a smoke test done?
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  5. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    Over boosting... need to log block 115 to see what the request is... pikey map I would imagine...

    <tuffty/>
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  6. Dani_B19
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    Dani_B19 Audi-sports own special child.

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    Or far too many mods on a standard map like me :) haha.
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  7. blued
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    blued Member

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    I'll need to ring round a few local garages and see if they offer this service.
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  8. blued
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    blued Member

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    If you are referring to the fault code it was over boosting because my N75 valve fell apart, the connection for the vacuum hoses literally came away from the rest of the unit. As per my first post this is now resolved. I'll get the codes cleared and am pretty sure I won't get the charge pressure error again because it is certainly not over boosting!

    How can it be the map? The car ran perfectly for the first 10 months, boosted to 15+ PSI, pulled hard right through the rev range...

    Can you log block 115 with free software?
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  9. blued
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    blued Member

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    I just had a thought, when I originally started looking at this problem I replaced the N249 valve by mistake, it was what Audi supplied me when I asked for the N75. Before fitting the valve the car hadn't made more than 4 PSI of boost for a couple of weeks. After I fitted it I got 15 PSI again and then it would drop back down to 4 PSI if I continued to accelerate (over boost due to the N75 leaking). I found it was the wrong valve, decided it suddenly boosted to be a coincidence and then swapped it for a N75. Could the N249 be what is causing my low boost now?

    I didn't get a chance to get the faults codes read last night, the weather has been terrible.
    #9
  10. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    get yourself access to full working vcds

    lite does'nt let you log beyond 020 I dont think?
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  11. blued
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    blued Member

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    Got the fault codes cleared, took it for a run and then checked them again, nothing stored. Wasn't able to log measuring blocks, the boy didn't have time. Looking at the Ross-Tech site there don't seem to be any restrictions on which block you can log with VCDS Lite, just that you can't log multiple blocks. I've got VCDS Lite and a cable so will try to get it working and logging tomorrow.

    EDIT: Just noticed this at the bottom of the page

    Shareware Limitation(s):

    You can only view groups 001-025. Groups 000 and 026-255 are blocked

    :(
    #11
  12. blued
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    blued Member

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    After some further googling last night I tried unplugging the MAF sensor before leaving for work this morning. It made no difference at all, could a faulty MAF cause this problem? I've read they don't always throw a code.

    I'm also getting about 50 miles less to the tank but that could be a combination of running with a faulty N75 and idling while defrosting in the morning. I've not done a tank since fitting the new N75.
    Last edited: Feb 7, 2013
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  13. blued
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    blued Member

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    I've got a laptop with VAGCOM 409.1 for the weekend so can do some logging. First here is a log of 115 from standing start through the gears -

    https://docs.google.com/file/d/0B0iLHKBO0Swgb0VmQVZWYUxVV2M/edit?usp=sharing

    Can someone interpret the data for me please?
    #13
  14. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    confirms its not trying to achieve boost request
    118 block, and 002 also

    clear fault codes.. check n75 is actually electrically connected and plumbed in correctly..
    #14
  15. blued
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    blued Member

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  16. blued
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    blued Member

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    Here is a picture of the N75.

    Attached Files:

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  17. blued
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    blued Member

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    Is there anything else I can check tomorrow while I still have this laptop?
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  18. Vex182
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    Vex182 Guess what I drive...

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    Im guessing you cleared all fault codes? Have you checked for any new ones?
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  19. blued
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    blued Member

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    Yes I did but nothing new has been stored. Before I cleared them I had the following -

    16514 - Oxygen (Lambda) Sensor B1 S1: Malfunction in Circuit
    P0130 - 35-10 - - - Intermittent

    I had this before and it was cleared and didn't turn up for a while, was told not to worry about it and it passed emissions last week no problem. Could it be related?
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  20. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    when I have seen this error before lambd adjust latched at +25% overfueling a lot..
    your lambda is only functioning on idle and crsuie throttle, so could manifest itself as a tendancy to be poor on fuel economy/performance until on boost and probable lumpy running and wanting to stall at junctions etc where its +25% from too much fueling
    #20
  21. Scullies
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    Scullies Well-Known Member

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    When I had the registered VCDS lite version, I was able to log any block as long as the first measuring block was between 001 - 025
    Worth a try
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  22. blued
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    blued Member

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    Thanks for the tip, will try that. I had a full version to use this weekend.
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  23. blued
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    blued Member

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    I don't have any symptoms of a bad O2 sensor, maybe using more fuel than usual but I need to run a full tank to prove that. The idle is fine and the car drives perfectly other than the lack of boost!

    Did my 002 and 118 logs reveal anything out of the ordinary?
    #23
  24. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    watch block 001 when its reporting that lambda fault and you will see what I mean re +25% fuel addition
    it is'nt necessarily lambda fault tho, wiring fault also likely

    i see mk3 ibiza cupras with this quite often
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  25. blued
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    blued Member

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  26. blued
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    blued Member

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    Does anyone know if I need to adjust the actuator so I get 6PSI on my boost gauge when the N75 is unplugged? If so which way do I need to turn the nut, towards the actuator or away from it?
    #26
  27. badger5
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    badger5 www.badger5.co.uk Site Sponsor

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    to add preload you turn outer nut towards actuator.
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  28. blued
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    blued Member

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    Thanks, I marked the current position and moved the nut about 2mm towards the actuator. I saw no difference on the boost gauge so I'm going to try bypassing the N249 valve at the weekend to rule it out.
    #28

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