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N75 Valve - Vag Com

Discussion in 'A3/S3 Forum (8L Chassis)' started by mnadeem1984, Sep 26, 2006.

  1. mnadeem1984
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    mnadeem1984 Member

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    [Sep 26, 2006]
    Is there anyway you can test if your n75 valve is faulty using vag-com. Also is it possible to check the MAF sensor? Nothings being flagged up on VagCom....
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  3. Tallpaul
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    Tallpaul Member

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    [Sep 27, 2006]
    Here's that post again with some more usefull info ;) :

    You need to log each of these blocks in 4th gear on a straight, flat piece of road from 2000rpm to the readline (this my take you over the speed limit so i can't condone doing this on a public road :) )

    You can log g/s airflow as a test of the MAF (block 002). You claim 218bhp so a figure of 166 g/s at ~6000rpm would suggest your MAF is OK. If you plot g/s v RPM on a spreadsheet chart the curve should also be fairly smooth.

    You can log N75 Duty Cycle, this is how 'open' it's holding the wastegate in % (block 118). This should be a good figure on full boost ie WOT at 3000rpm = ~70%+? Ideally 95% at 3000rpm but that's not hard and fast, really depends on your boost pressure:

    You can also log requested boost and actual boost which is a good check for a leak (block 115). If you requested boost is pretty much meeting actual then your N75 is OK. As for what your actual boost pressure should be... Well lets say your peaking @ 18psi (a sensible number for a remapped K03s)... VAG-COM measures boost in mBar but this figure includes atmospheric pressure so you'd need to apply this calculation: (Boost-1013.25)/1000x14.50377. In other words you'd be looking for a peak boost value of 2300-ish in VAG-COM (assuming you are peaking @ 18psi). If you have a boost gauge then you'll know what you should be getting. Again plotting both requested and actual (2 seperate lines) v RPM on a chart will make it easier to interpret.
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  4. squale
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    squale New Member

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    [Nov 3, 2006]

    Hi !!

    On my ABT S3, Duty cycle is max at 84.3%, does it mean that my N75 F is faulty ? Moreover i have flat spots in boost and the target boost is not reached.. any idead ? (My Maf is ok)

    Thx !!!
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  5. Tallpaul
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    Tallpaul Member

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    [Nov 3, 2006]
    Small boost leak?

    Duty cycle is probably ok, but by how much is your actual boost not meeting requested? At most points over the rev range it won't but probably between 4000 - 5000rpm it should be very close.
    #4
  6. squale
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    squale New Member

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    [Nov 3, 2006]
    I'll post a graph in some minutes, btw if i had a boost leak i think the N75 would be near 100% duty to compensate ??
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  7. Tallpaul
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    Tallpaul Member

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    [Nov 3, 2006]
    I don't think the N75 is allowed to close the wastegate 100%, one of the many in built safety features of the ECU.
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  8. squale
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    squale New Member

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    [Nov 3, 2006]
    Maybe but you told about 95% duty, thats not my poor 84.3%
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  9. Tallpaul
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    Tallpaul Member

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    [Nov 3, 2006]
    84.3% is low, should defo be hitting 95% at 2500-3000rpm.

    Your N75 could be faulty, then again it might not. I take it from your signature that your car is remapped?

    Post up the boost graphs, it may give a clearer picture?
    #8
  10. Tallpaul
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    Tallpaul Member

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    [Nov 3, 2006]
    Might also be worth checking the CF's for the timing on each cylinder...

    and perhaps checking the throttle body...

    loads of things it 'could' be... No fault codes then?
    #9
  11. GarryA3
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    GarryA3 Member

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    [Nov 3, 2006]
    Hi guys,sorry to butt in but you seem pretty clued up on the working of the audi engine.Would the N75 valve being faulty cause my problem??
    Here is my thread,

    http://www.audi-sport.net/vb/showthread.php?t=29880

    Just so i can either discount it or say it maybe a possibility that its this thats faulty.Thanks.
    #10
  12. Tallpaul
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    Tallpaul Member

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    [Nov 3, 2006]
    Sorry fella, i don't really know that much about the 1.8T - i know even less about oil burners...

    If you paid a garage to rectify this fault recently then i'd go back to them and ask questions.

    Any self diagnosis is gonna require VAG-COM.
    #11
  13. dubhyper
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    dubhyper Illegally Street

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  14. LaSarthe&Back
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    LaSarthe&Back Member

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    [Nov 4, 2006]
    Can the logging of MAF readings and Actual Boost vs requested be done in the shareware version of VAGCOM (3.12 btw)??

    Andy
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  15. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    IIRC you can only log the first 25 measuring blocks on shareware VAG-COM so you can only log the MAF, not boost.
    #14
  16. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    Hey guys, I've done a few tests with VAG.com. Followed your instuctions Paul, and just wanted to check a few things. Ok I still need to do MAF test later, but I've done the test for Block 118 (N75) and 115 (Boost). Now for the N75 reading it peaked at 2440 rpm with N75 being 91.4%, now is this normal? @3000rpm it was 48.6% too low?.

    Second question was boost pressure. Now it logged "Cmd Pressure" & "Press @ Intercool" so I wasn't sure if that was requested vs actual boost. But this is what I got. Now there's a bit of a difference and I was wondering if that was due to my FMIC and SMIC being connected instead of the one FMIC? anyway any help would be much appreciated as I am new to VAGcom and wanna learn more :jump:

    [​IMG]

    P.S. I did the little calculation for finding boost pressure and I think mine is running at 12psi, is that around normal for a 225 S3? figures were (1870mbar @ 4680rpm) :beerchug:
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  17. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    errr, did you lift of the throttle or did the TCS cut in when you did those logs?

    what gear were you in?
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  18. loftgroover
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    loftgroover Member

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    [Nov 5, 2006]
    Hi Defratos,

    Your graphs are interesting, what caused the dip in the middle, did you back off or change gear?

    I have done some tests with my 2001 S3 with SPS3 comparing the different boost settings available of the Revo SPS 3. As you can see, my actual boost is a little way off the requested boost in both instances. I am suspicious i may have a small leak somewhere. Poss the same for you.

    [​IMG]
    #17
  19. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    Hummm, ok I think I did let go a lil "on comin car" didn't realise at first lol. I'll do the test again later and see what happens. I was in 4th gear from 2000rpm -redline
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  20. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    was my boost pressure reading of 12psi sound right?
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  21. ChriS3
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    ChriS3 hud at ye bam

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    [Nov 5, 2006]
    Standard car, no remap? Sounds about right.
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  22. loftgroover
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    loftgroover Member

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    [Nov 5, 2006]
    I think 12psi is a little low.

    If you look at my graph you can see maximum boost is about 1.5bar which is 21.75psi.

    I would expect aou 14-15psi for a standard S3..

    someone ( paul! ) correct me if im wrong
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  23. ChriS3
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    ChriS3 hud at ye bam

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    [Nov 5, 2006]
    I thuoght the S3 ran at 0.9bar in standard form? 13psi. Might well be wrong :)
    #22
  24. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    12psi sounds spot on to me.

    Loftgroover... Are you just altering the boost settings? have your tried playing with the timing too? What fuel and mods do you run?
    #23
  25. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    humm, well anyway here's another graph (no dip in this one), still a difference between the two (possible leak?)

    [​IMG]
    #24
  26. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    Defratos... this is a plot of boost on a stock SEAT Leon Cupra R (210bhp). Not a direct comparison but basically the same engine, you can see how boost meets requested very well. Your plot is a little odd, could your pressure drop be due to your FMIC?

    [​IMG]
    #25
  27. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    yeah I think so, Someone on here has told me I'd get a huge difference in pressure between the two ICs. Hopefully gonna be upgrading soon to just the single, maybe that'll sort it out. cheer for the help though :beerchug:
    #26
  28. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    The thing is, the S3 on stock boost doesn't need a FMIC. As your plots show, you are actually losing power because of the extra volume. The two stock SMIC's are very capable of maintaining a sensible inlet temperature.

    If i were you, i wouldn't waste more money on expensive mods that give negligable gains. Go get yourself REVO and an SPS3 and keep your FMIC. If you run V-Power then with that FMIC you'll be able to wind up the boost and timing and watch your car fly.
    #27
  29. loftgroover
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    loftgroover Member

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    [Nov 5, 2006]
    Paul,

    Im running fuel at setting 7 on the SPS using V-Power. Slightly cooler plugs.

    I think there might be a small boost leak as your SEAT graph demonstetates. What you think?

    Also, ive logged the data on a friends S3 and get the following, boost not following requested and then being well over the requested ( N75 checked and working OK), any ideas? What casues the dip in the middle?

    [​IMG]
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  30. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
    hmmmm, your timing is a little agressive; and maybe you are running too higher boost too?

    Try Low Boost 9 Timing 6?
    #29
  31. Tallpaul
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    Tallpaul Member

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    [Nov 5, 2006]
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  32. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 5, 2006]
    Hey there mate, ok I know what Revo is but whats a SPS3? and V-power?
    #31
  33. loftgroover
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    loftgroover Member

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    [Nov 5, 2006]
    Hi Defratos,

    Sorry, SPS 3 is a Revo product that allows the user to adjust the boost
    and ignition timing that the ECU uses on the car to enhance performance., But, as Paul is indicating, this should only be used with some sort of monitoring software such as VAG-COM so the user can monitor the effects.

    V-Power is Shell's new product name for Optimax, a pump fuel with 98 (99?) RON that allows the engine to run more aggressive ignition timing safely.
    #32
  34. loftgroover
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    loftgroover Member

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    [Nov 5, 2006]
    Hi Paul,

    No, i have the later SPS version with high and low boost options.

    Are we refering to my car (first graph) of my friends car? I have logged my CF on all cylinders and almost none is applied, it seems the 1.8T has fantastic active knock control, plus im running v-power.

    As for my friends S3 ill try and log CF as well and bring the boost down a little.

    You private user or have business in cambridge?
    #33
  35. Tallpaul
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    Tallpaul Member

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    [Nov 6, 2006]

    lol, very much an amateur! :jester:
    #34
  36. loftgroover
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    loftgroover Member

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    [Nov 6, 2006]
    Ha ha, ill start ignoring your advice then :laugh:
    #35
  37. Tallpaul
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    Tallpaul Member

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    [Nov 6, 2006]
    I wondered why anyone listened in the first place! :)
    #36
  38. Defratos
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    Defratos You’re Dethpicable!!

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    [Nov 6, 2006]
    Hey there guys I want to ask something. How do I go about keeping the same pressure throughout the exchange from Turbo to IC to Manifold? I've heard keeping the diameter of the pipes the same throughout would help. Just wanted to ask whats the Forge FMIC outlet size is? and what size outlet should I not go over? I've heard 2.5" outlet is the biggest any bigger will lead to pressure drop?
    #37
  39. Tallpaul
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    Tallpaul Member

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    [Nov 6, 2006]
    i see you're ignoring the remap advice then...

    2.5" Intercooler Hosing in sufficient. IIRC the Forge FMIC uses either 2" or 2.5", i don't think it's as wide as 3".
    #38
  40. loftgroover
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    loftgroover Member

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    [Nov 6, 2006]
    Unfortunatly the laws of physics stse that any obstruction in the system will cause a pressure drop, the more obstructions, the greater the drop in pressure.

    In order to have as much of the compressor outlet pressure at the manifold you will need to have as few bends as possible ( and where there are make them as gradual as possible) and you will need a free flowing intercooler. ( others on this forum will have more experience so ask about the best coolers)

    Remeber though, you need to trade carefully between free flowing intercooler and charge air temp reduction. Its no use having very high pressure air in the manifold if its at 150 deg C!

    Turbocharger outlet pipes are sized quite specifically in relation to the gas velocity leaving the turbo, and too large a pipe will become an issue, what that size is though, i have no idea!
    #39
  41. loftgroover
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    loftgroover Member

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    [Nov 6, 2006]
    You will gain far more in the short term from a remap and good fuel..

    you only need to worry about the charge air cooler when it is the only item in the system thats a restriction, and im guessing youre nowwhere near that yet!
    #40

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