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Loosing boost!! Any ideas??

Discussion in 'A3/S3 Forum (8L Chassis)' started by FinnMc1, Apr 19, 2011.

  1. FinnMc1
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    FinnMc1 Member

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    [Apr 19, 2011]
    Hi Guys,

    Not used the vagcom cable much yet but heres my first log.

    The problem is im loosing boost about 3500rpm. sometimes completely andother times like for this log it flutters kinda. like its not sure what itdoing boosting or releasing. Ive read it can be the N75 valve for this kindaproblem but wondering if any of you might be able to have a look and see whatyou think. I know the MAF reading are low but the problems happen with orwithout it plugged in.

    http://i1108.photobucket.com/albums/h419/finnmc1/S3 logs/S3Log.png

    Cheers guys.
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  3. S3 Nattie
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    S3 Nattie Quattro ist für sissies

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    [Apr 19, 2011]
    Your boost is off the scale for vag com so 22+ boost pressure your seeing. Do you get the fluttering noise when coming of the throttle, could be your DV if so and you could get a MBC to cap your boost down a bit.
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  4. FinnMc1
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    FinnMc1 Member

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    [Apr 19, 2011]
    No itt flutters or looses all boost(depending on how its feeling on the day) when im under full acceleration. What could of changed to cause it to overboost because its only started about 3 months back and its getting worse. I thought ive seen other peoples logs reaching 2500mbar etc.
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  5. beachbuggy
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    beachbuggy Well-Known Member

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    [Apr 19, 2011]
    From your logs it looks ok to me. Your actual is less than 1 psi above the requested which is ok.

    How you telling you are loosing boost? If it's by a Boost gauge then don't take what it shows you as an accurate description of your boost. Basically the Turbo boost will reach a peak and then settle down to a given boost level, this will be seen as a spike of boost which will drop away as the rpm/load rises.
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  6. FinnMc1
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    FinnMc1 Member

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    [Apr 19, 2011]
    No this is serious. like yesterday i went to overtake and then it just totally bogged down and i lost all power and had to pull in to a row of traffic halfway through over taking!! not what you need haha.
    like to me it sounds and feels like its dropped off boost totally.
    This log tonight it just felt like it fluttered. I dont have any boost guage its just an assumption im making that its something to do with the boost or something controlling the boost.
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  7. beachbuggy
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    beachbuggy Well-Known Member

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    [Apr 19, 2011]
    Don't quite agree

    max boost is 2470 ( 3000 Rpm) which is 1470 actual ( 1000mb is atmospheric ) which is boost of 20.8psi.
    Last edited: Apr 19, 2011
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  8. S3 Nattie
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    [Apr 19, 2011]
    In the log your not actually loosing that much boost and your N75 looks ok to me. Your MAF values are really low but apart from that and your pretty high boost it looks ok. You got any logs of your exhaust gas temperatures and lambda values.
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  9. beachbuggy
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    beachbuggy Well-Known Member

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    [Apr 19, 2011]
    Ok I see. From the logs it doesn't look like you have a leak, I would take a hunch and wage 5p that one of your coil packs is on the way out.

    All else may seem fine but under heavy load it stumbles sounds like coilpacks.
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  10. S3 Nattie
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    [Apr 19, 2011]
    Is that not his max requested boost 2470mb. His actual peak boost is 2520 (14.7 = 1013mb atmospheric) which is 22 psi of boost pressure.
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  11. FinnMc1
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    FinnMc1 Member

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    [Apr 19, 2011]
    I know on the log the boost is reading ok but it feels like it looses boost when driving. I need a log when it messes about majorly but tonight it wasnt too bad typically. it is only under hard acceleration and only around the 3500rpm area then after 4400 or so it picks up again.
    I did have more logs of other blocks but my harddrive crashed last week and lost it all. Thats good to know that this Log seems to look ok anyway. Ill see if I can get the coil packs checked then
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  12. beachbuggy
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    beachbuggy Well-Known Member

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    [Apr 19, 2011]
    Yes you are right. I was just using the requested as an example, as the difference between requested and actual was only 0.7psi so not really a problem and certainly no leaks, Vagcom should easily be able to 22psi. It's only the MAP that runs out at 30psi ( I think)
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  13. beachbuggy
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    beachbuggy Well-Known Member

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    [Apr 19, 2011]
    Check the pipe to the FPR if that's got a leak then it wont fuel properly. log 032 to see the fuel trims.
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  14. S3 Nattie
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    [Apr 19, 2011]
    You could get a log of 31, 112, 20 to get your lambda, correction factor and exhaust temperatures. I think its blocks 15 and 16 which will give you your misfire could so hopefully should see something if your coil packs are on their way out


    Im not 100% but remember reading recently that 2550mb was the max vag com can read up to.
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  15. FinnMc1
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    [Apr 19, 2011]
    Ok ill try getting a log of those tomorrow and see what I get. I had a glance at the fuel trims earlier and i think the short was about 0.9%+or- cant rem and the long was 4%+. ill have to check tomorrow though to be sure. If I log those other ones tomorrow do u want just the same rev band as today or all the way to redline or wat.
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