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  • Strange boost issue

    Hi guys,

    Recently my 3b developed a strange problem, when in low rpm I floor it it boosts to 0,5bar and then starts fluttering,but still builds further until 0,8 to then builds fast to 1.4.
    Of coarse when this fluttering happens you feel this in a hesitation in the power. All boost pipes are new apart from the o-ring, mark h mod will be done shortly, also I suspected the n75 but replacement showed no difference.
    In higher rpm it does not happen or is not noticeable because the boost builds faster past this point.
    Anybody has a clue about what can be the cause of this problem?

  • #2
    Check your diverter valve, the diaphragm may be split. The actuator line should hold vacuum.

    Also of course you should do a boost leak test.
    Last edited by newsh; 25 December 2020, 17:29.

    S2 Coupe 3B Project


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    • #3
      Alright, I tested the diverter valve and it holds vacuum fine, but when I applied pressure of 1 bar it slowly loses pressure,does this means it is shot?

      I did the mark H mod and it was obvious it was leaking on the o ring of the intercooler because after this the surging/fluttering is completely gone and the car pulls strongly until redline without any hesitation.

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      • #4
        Originally posted by nick View Post
        Alright, I tested the diverter valve and it holds vacuum fine, but when I applied pressure of 1 bar it slowly loses pressure,does this means it is shot?

        I did the mark H mod and it was obvious it was leaking on the o ring of the intercooler because after this the surging/fluttering is completely gone and the car pulls strongly until redline without any hesitation.
        It’s just a diaphragm so I would have thought if it leaks one way then it would leak the other and when the diaphragm goes it leaks a lot!
        On the other hand, a vacuum tends to seal a leak in a hose or a loose clamp, pressure will open the leak. Have you tried with a new piece of vac pipe and a small zip tie to clamp it?
        If you pressurise either of the large pipes it will leak unless it has pressure on the vac nipple as well.

        Looks like you’ve found your main leak at the IC O ring though, great stuff!

        S2 Coupe 3B Project


        Ur quattro restoration

        S2 Avant

        Boost is the new rock and roll!
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