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How use VAGCOM/VCDS to test for boost & vac leaks

Discussion in 'A3/S3 Forum (8L Chassis)' started by finesse, Oct 29, 2010.

  1. finesse
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    finesse Active Member

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    Looking for help on how to use VAGCOM/VCDS to test for boost & vac leaks?

    Thanks
    #1
    stuart_tate41 likes this.
  2. Welly
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    Welly VX220 SC Driver :)

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    Easiest way is to check block 032.

    There are two fields in the block, and both belong to fuel trims.

    Left hand one is short term adaption, right hand one is long term adaption. Left hand one is the one to look at in this instance.

    Make a note of these two figures. Reset the fault codes (even if there are none), as this will clear the fuel trim data back to 0% for both blocks.

    Then start the motor and log block 032. If the value in the left hand block steadily climbs to or past the 3-4% area, it's normally a good indication of a leak.
    #2
  3. finesse
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    finesse Active Member

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    Thanks Welly, you the man
    #3
  4. DaveA3
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    DaveA3 Audi A-Trizzle!

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    what should it be if there are no leaks welly mate?
    #4
  5. Welly
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    Welly VX220 SC Driver :)

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    As close to 0% as possible..... It means it's neither adding, nor taking away fuel at idle.
    #5
  6. Prawn
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    Prawn My other car is a MINI!!!!

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    Will be trying this in the morning!

    Leggy suggested that at 3000rpm under no load the real time MAF reading should be exactly 10g/s on a car with no leaks....
    #6
  7. Welly
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    Welly VX220 SC Driver :)

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    Not tried this, but did see it. Would be interested to know if it works from someone who's tried it....
    #7
  8. Prawn
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    Prawn My other car is a MINI!!!!

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    well, it works in mine. holding the revs as accurately at 3k as I can I see bang on 10g/s, and to my knowledge, I don't have any leaks.

    GOing to check the fuel trims in a mo see what that gives me to confirm
    #8
  9. Essflee
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    Essflee Active Member

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    I did try this too with my mates liquid gauge, held the revs at 3000rpm and I was only showing 8g/s...

    Went to Jabba yesterday and they smoke tested the system and I do have a boost leak by the inlet manifold, going to put the new pipe on Monday as Jabba didn't have the part in stock, once I've done the fix I'll try the liquid gauge again,

    Let you know how I get on...
    #9
  10. voorhees
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    voorhees Moderator Staff Member Moderator

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    Thanks thats a good bit of info
    #10
  11. nick4501
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    nick4501 Member

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    Does the 3k rev method and block 032 apply to 1.8t A3's too?
    #11
  12. Essflee
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    Essflee Active Member

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    Prawns is an A3 1.8T and it seems to work on his...
    #12
  13. nick4501
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    nick4501 Member

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    Good point! - Cheers, will give it a try.
    #13
  14. Lloyd149
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    Lloyd149 Member

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    Cheers, will try this too.

    Sticky?
    #14
  15. Danny Cawsey
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    Danny Cawsey Cawsey

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    what should my boost gauge be reading on idle with a stage two map and forge mbc set to 1.5 bar 1999 aoudi s3 apy?
    its reading -0.7 bar is this correct?
    #15
  16. Prawn
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    Prawn My other car is a MINI!!!!

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    Just tried the fuel trims test on mine, before resetting it was -0.4% short term, and -4% long term.

    Reset them and the short term didn't move from 0 at all for 5 mins idling. drove 30 miles home, and short term is 0 still, and long term is -3.9%

    Does this sound fairly normal to you guys?

    If it's pulling out 4% fuel long term, does that imply the map is running rich as standard, and it's possibly got a smallish leak somewhere? or being a generic map, will they all adjust a few % up or down to suit individual cars?
    #16
  17. Welly
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    Welly VX220 SC Driver :)

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    Short term trim sounds spot on dude.

    Long term trim's acceptable tolerances are between +/-10%, and you are well within that. Bottom line is that it's a generic map, and every engine is different...

    The ECU won't throw the EML for fuelling until +/-25% is breached.
    #17
  18. finesse
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    finesse Active Member

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    I thought the short term adaptation is considered fine -+ 10%?
    #18
  19. Mpathe
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    Mpathe 1st gear

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    mine reads on idle -20 which i -1.3 bar so you might have leak some where
    #19
  20. Welly
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    Welly VX220 SC Driver :)

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    Yeah.....? I don't understand what you're getting at here dude....
    #20
  21. sekenzo
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    sekenzo Member

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    Did both the methods and my results are:

    Rpm at 3000rpm is between 10.3-10.9
    Short term fuel is at 0.8 and long term is at 0 after 5 mins

    Does this look like I have a leak?

    Also, how would my boost gauge behave if there is a leak?
    #21
  22. Essflee
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    Essflee Active Member

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    Sekenzo,

    Not sure about the fuel trims but the theory of holding 3k revs and your G/s maf reading would suggest that your car is fine, I was told that the tolerance is 0.9, as your seeing 10.9 would suggest your car is fine...
    #22
  23. takworldwide
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    takworldwide Member

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    i might sound alittle special here but do you hold 3000rpm stationary or whilst moving(3rd, 4th, 5th Gear)?

    thanks
    #23
  24. voorhees
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    voorhees Moderator Staff Member Moderator

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    At a standstill.
    #24
  25. takworldwide
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    takworldwide Member

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    do you think it would work on a AGU (no MAP sensor)?
    #25
  26. murran
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    murran Active Member

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    plus or minus 10% is what the ecu works on.
    if its outside these perameters the management light is supposed to come on showing up fuel trim faults.
    whether these faults are due to air leaks/injector faults/dodgy air mass's is anyones guesses!
    #26
  27. Garber
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    Garber New Member

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    Hello everyone this is my first post ive been lurking around the site gathering info to try and resolve 2 faults on a 02 Audi A3 1.8 T AUM engine
    error codes are
    2 Faults Found:

    17608 - Boost Pressure Control Valve (N249): Mechanical Malfunction

    P1200 - 35-00 - -

    17544 - Fuel Trim: Bank 1 (Add): System too Lean

    P1136 - 35-00 -

    up to now i have replaced 2 breather hoses 06A103247 & 06A103213AK
    ordered a Recirculating closed loop Dump Valve which i hope will clear the Boost Pressure Control Valve (N249): Mechanical Malfunction
    just had a look at Block 032 whilst stationary idling at the moment i have a reading of:
    7.9 Idle O2 Adapt & -3.1 Run O2 Adapt
    because the first reading is high could this be because the DV is faulty & creating another vac leak as well as giving no boost pressure ?
    cel comes on after about 15 miles 23 mpg is not good at all even when driving like miss daisy :(

    update
    Just found another split pipe under inlet manifold it comes out of a T piece to the underside of the inlet manifold I'm not sure about the part number i think its
    06A 133 783 AT could anyone confirm this will fit A3 1.8 T AUM engine Ive cobbled something together for now to see if it cures:
    17544 - Fuel Trim: Bank 1 (Add): System too Lean fault
    Last edited: Dec 31, 2010
    #27
  28. Garber
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    Garber New Member

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    Fingers crossed think Ive sorted faults:
    17608 - Boost Pressure Control Valve (N249): Mechanical Malfunction
    P1200 - 35-00 - -
    17544 - Fuel Trim: Bank 1 (Add): System too Lean
    P1136 - 35-00 -
    Replaced split vac pipes & old DV
    bought a piston type from ebay see if it lasts longer than a 710N
    Link to before and after boost charts could anyone tell me if 2nd chart looks about right for a standard 1.8T
    Last edited: Jan 23, 2011
    #28
  29. vrbob
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    vrbob Thats no Moon, Thats a space station!

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    Tried this method out yesterday while doing some tinkering with a couple of other guys from here and its a good quick way to check to see if you have any leaks that need investigating furthur.

    My car from the results is looking pretty leak free and held 10g/s at 3k rpm so all is good cheers for the guide chaps
    #29
  30. Wingnut Express
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    Wingnut Express Audi sponsored by Mastercard

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    Hi Guys

    I tried the Block 032 test last night to see if if there were any leaks, but would really appreciate some advice to clarify the results

    I ran the car for a short while to allow it to warm up and then I ran the test.

    -1.3% on the Left - Short Term and - 6.3% on the right - Long term

    I then cleared the faults as suggested and these results differed to the below

    -0.4% rising to -1.7% Short term & 0.0% on the long term

    I already have concerns that the car is running lean, but I do not understand these results enough to be able to make an eductaed decision?

    Sadly it was too late at night to be holding the engine a 3k to test the other way

    Thanks in advance

    #30
  31. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    -6.3% LTFT is more likely to indicate you have a leak under boost... a vacuum leak will show as a positive figure in STFT but may well adapt to a negative value in LTFT... LTFT's will take a little while to adapt...

    If you suspect you have a fuel issue then you need to log blocks 001, 031 (as you have a wideband ECU on your AMK S3) as this will show lambda control values (001) and requested AFR vs actual AFR (031)...

    <tuffty/>
    #31
  32. Wingnut Express
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    Wingnut Express Audi sponsored by Mastercard

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    Thanks Tuffty I will try this again tonight, as I balls up logging Blocks 001 & 031 last night. (driving and clicking go on the laptop!)

    Cheers Ian
    #32
  33. <tuffty/>
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    <tuffty/> Badger 5 Edition Staff Member Moderator

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    Click go before driving off then just look at the run rather than all the surrounding data... safer.. also... hover the mouse over the marker button and tap the tounch pad prior to a run... you can also use the 'right arrow' cursor key too...

    <tuffty/>
    #33
  34. Vex182
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    Vex182 Guess what I drive...

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    Sorry to drag this up, if I have a positive reading in the left box. The number went from 0 to 3% in a few minutes after resetting, what is that telling me?
    #34
  35. myke
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    myke Member

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    Probably got a leak, A smoke test would be the next step to find the leak, the 1.8t is well known for leaks.
    #35
  36. Vex182
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    Vex182 Guess what I drive...

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    I know this is pretty old now, I had a smoke test last week and there was a small leak all sorted now. Trims were reset 200 odd miles ago and now it's saying 0.2% idle and -3.1 part throttle. Sound better now? The car feels like it boost better.
    #36
  37. ryanwilson1987
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    ryanwilson1987 New Member

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    What about the maf test on a 1.9 130? I just done it on mine and it was 51.5 g/s
    Last edited: Jul 13, 2014
    #37

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