loss of power and missfire whilst boosting

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  • gmac78
    S2Forum Maniac
    • Oct 2009
    • 928
    • Home: Scotland

    #1

    loss of power and missfire whilst boosting

    Hi Guys

    Needing some advice on a problem that is doin my head in!!!

    My car was previously running perfect in stock condition.

    Borrowing a loaner ecu from paul which has been homefried, most impressed with the power/torque increase, however it would missfire on full boost at first. It has been getting progressively worse over the last few weeks where now it feels like if ur driving steady off boost (vacuum on guage) say in 2nd or 3rd you can feel the power decrease and a constant missfire, not a violent missfire but a subtle one. The engine feels like it bogs down a bit.

    When i do go to boost fully it feels like there is a lack of power even although it seems to pick up on the gauge ok. Other times it will start to missfire when in the early stages of boosting causing me to back off.

    Changed plugs to the suggested BOSCH ones, checked boost pipes for obvious tears but nothing untoward found. Only part i didnt check was the intercooler o ring. If this is gone would it cause these problems?

    Changed leads for known good ones of a 90 20v and same occuring. Just checked distributor cap and rotor arm, distributor spark point surfaces seem to be fairly black in colour with some kind of debris on the surface. Cleaned these up and look ok now i think. How bad to these points have to be to cause a problem?

    Where can i get a hold of all the kit needed to properly test for boost leaks just incase i missed something?

    Please any pointers would be much appreciated.

    Thanks in advance for any help you can give me.
  • Le S2 Audi
    S2Forum Possessed
    • Jul 2009
    • 3805
    • Home: Scotland Current: England

    #2
    sounds like the same issue I have had with mine when I also put in a Homefried ECU & it sounds the IC O ring.

    I am doing the Mark H Mod on mine tomorrow...

    Depending on my Hangover...

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    • iDub
      S2Forum Enthusiast
      • Oct 2006
      • 182
      • Country: United Kingdom

      #3
      Does sound like a boost leak to me. The extra boost from the homefried ECU has probably blown through a weak point - as you say quite possibly the IC O ring. Andy P is your man for boost leak test kits:

      Audi S2:

      Avant! Ye scurvy landlubber...

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      • gbleenz
        S2Forum Fanatic
        • Jan 2008
        • 74
        • Country: New Zealand

        #4
        I'm not able to offer too much technical knowledge, but I was experiencing a similar issue with my coupe a couple of years ago.

        I had our local Audi service dept take care of it. I'll try to find the service history. For memory, I *think* the problem originated from the inlet manifold...
        --
        '96 S2 Coupe
        '84 ur Quattro
        '72 MGB

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        • 20V khan
          S2Forum Buff
          • Sep 2008
          • 25
          • Country: United Kingdom

          #5
          I have been experiencing the same symptoms also with intermittent starting issues. I took my dizzy out to find the metal cog very worn down. Waiting on a new cog to replace my existing one and hopefully it will solve my issues. I think you should check for play in the rotor head and if there is play pull the dizzy out and check the cog. I know its not my IC O ring as I only replaced it a few months back and havent had any upgrades done.

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          • Le S2 Audi
            S2Forum Possessed
            • Jul 2009
            • 3805
            • Home: Scotland Current: England

            #6
            All these are worth checking....

            but I am sure its the IC O ring leaking... Its the exact same issue I had when I put the homefried ecu in as I didn't feel any benefits from it and the subtle misfire only really shows in a high gear and ONLY around 3.5-4.2K RPM...

            I had it fixed but its started again so I am going to fit the Mark H Mod at the weekend... Too Hungover today and its too COLD....

            & as you said it's the one you didn't check.... but from what I gather its not easy to just see it, as it only leaks under pressure... BUT I am no Mechanic so its just my opinion!!!

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