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N75J and limp mode (overboost problems)

Discussion in 'A3/S3 Forum (8L Chassis)' started by pure, Jun 17, 2004.

  1. pure
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    pure Member

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    [Jun 17, 2004]
    After recently installing the N75J valve, I am extreemly happy with it. I have finially realised what limp mode is after experiencing this since the new valve.

    Basically I seem to hit limp mode when the car is not fully warmed up, I'm in 6th doing between 70-80 and I need to accelerate. Bang, I hit limp mode. Then after a few mins it seems to clear it self and boost again. Usually hit it once on my journey to work in the morning.

    Anyways, I guess that hitting limp mode is some kind of safety feature to stop the turbo exploding when overboosting!

    I had a quick search on the tinternet and found this interesting link.

    http://www.izvw.com/overboost.html

    Basically it is a method of restricting the boost to a max level.

    Has any one tried this mod on their S3?

    Cheers, Greg

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  3. Gambba
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    Gambba Active Member

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    [Jun 17, 2004]
    Well you may also want to try the 'H' or 'C' variants of the N75 as these offer different levels lower than that of the 'J', and as discovered for some cars the 'J' is just too much.

    I would suggest trying the 'H' as this is one which ECS market so imagine it is fine for almost all 1.8T's without going into limp.
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  4. Mike.M
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    Mike.M Well-Known Member

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    [Jun 17, 2004]
    increase of boost = more power
    #3
  5. Gambba
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    Gambba Active Member

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    [Jun 17, 2004]
    [ QUOTE ]
    RichA3Turbo said:

    I think you may have got that the wrong way round... the H is more aggressive than the J, so will hit limp mode MORE often. The J overboosts less than the H.

    Rich

    [/ QUOTE ]

    Not according to the stuff I've seen, the H just holds boost across more of the range so feels more agressive but the J spikes higher...........having said that if you read the below link you'll start to agree with me, but then at the very end things get turned on their head (You'll see what I mean!).

    Some nice VAG-COM logs showing the difference between H and J
    #4
  6. dbm
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    dbm Active Member

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    [Jun 17, 2004]
    Greg, interesting that you are getting limp-mode. I've never experienced it in my S3, and we have similar set-ups. When you say that you're car isn't warmed up, what do you mean?

    Ta,
    Dan
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  7. S3DBW
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    S3DBW Member

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    [Jun 17, 2004]
    Quote:
    "I had a quick search on the tinternet and found this interesting link.

    http://www.izvw.com/overboost.html

    Basically it is a method of restricting the boost to a max level.

    Has any one tried this mod on their S3?"


    I am currently running with this setup and the "H" valve and it works very well. Its essential for the "H" valve as stated elsewhere on this post it is a bit more aggressive than the "J" valve.

    It takes a bit of experimenting to get it just right, but I have been running at peak boost pressures of around 1.2bar on an otherwise standard car for the last 20K miles with no adverse effects whatsoever and the increase in performance is very noticable.

    I would advise though, that the onset of limp mode is very car dependent, on some cars it can cut in at just over 1.1bar, on others, such as my own it needs at least 1.3bar to initiate.

    As with everything in life, moderation is the key, that and an accurate boost gauge!!

    regards
    #6
  8. pure
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    pure Member

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    [Jun 17, 2004]
    hmmm, happned on the way home, spoke to soon, was on m-way, been driving for about 25mins, then i needed to put my foot down accelerating from 70mph, takesoff...then blam...limp mode...lasted for about 5mins b4 it started to boost again. Might have to order 1 of those boost regulators I think.
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  9. Gambba
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    Gambba Active Member

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    [Jun 21, 2004]
    [ QUOTE ]
    peteTDI said:
    if you have a faulty N75 valve will it show a fault on vag.com?

    [/ QUOTE ]

    Yes. It may just show something like intake pressure leak and suggest the N75 as being the problem, or it may well state an N75 fault.
    #8
  10. S3DBW
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    S3DBW Member

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    [Jun 21, 2004]
    You may well need to use Vag Com to clear the DTC fault codes. In the early days of experimenting with the "H" valve and the overboost solution I regularly hit the limp mode until I got the settings optimised. Vag Com was the only thing which would clear it.

    Some people have success with simply stopping and restarting again, but it never worked for me

    regards
    #9
  11. pure
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    pure Member

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    [Jun 21, 2004]
    I just checked the car over and I did the following things which seemed to clear limp mode:-

    Adjusted N75J electrical cables (they were pulled very tight, I moved then and gave them a little more slack)

    Changed my mapping back to standard, then back to Optimax.

    Took it out for a test run and it is running fine again now.

    I think the reason I could have possibly been stuck in limp (low level boost) mode was because the N75J wires were being pulled and disconnected it.

    Would disconnecting the N75 limit your boost, in the same way running in limp mode would?
    #10

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