Missfire under WOT S2 ABY Avant

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  • Tonybolony
    S2Forum Maniac
    • Dec 2011
    • 636
    • Country: Wales

    #1

    Missfire under WOT S2 ABY Avant

    This happened today, after 10 seconds ish of wot. It's already dark outside, and I hav'nt a garage. I know there are many possible causes, but would welcome any advice on where to start looking.
    The MAF plug is removed and cleaned/sprayed regularly.
    The boost pipes (RS2 Intercooler) are Roose, and only a few years old, and altho I have no access to a Leak Test kit, I don't suspect a leak, as the pipework looks fine.
    Over Xmas hols I pulled the Plugs, and they all looked clean and dry; with Biscuit coloured ceramic tips. (No reason to suspect any probs at the time, just bored!)
    Last summer I replaced the cabling to the Coil packs.
    Fuel consumption good (28mpg on a gentle trip to France only 3 weeks ago)
    On initially burying the pedal, she spools up to 18/19 psi, slowly dropping to 14/15psi after a few seconds) but could this drop be due to a missfire (and not necessarily a leak)? My thinking is that the boost would drop due to the loss of a cylinder??
    It is an irregular miss, which prob means it's not one specific cylinder??
    I've thought about looking for any arcing with engine running, after dark, but can't do it tonight.
    I bought a set of leads to connect a Sealey Code Reader, but won't work, so can't give any fault codes. I Have never used a code reader before- if it turns out to be a coil; would the reader tell me which one, or is this trial and error?
    I have just ordered a new breather pipe (The 90deg short rubber one that is on the back of the cam cover steel pipe) as it is split, but surely this could'nt cause my issue??
    I'm far from an expert, and any help to stop me running off on an incorrect and expensive tangent would be gratefully received.
    Ps the ecu is Homefried.

    Any help would be appreciated
  • driftin jo
    S2Forum Fiend
    • Sep 2007
    • 2222
    • Country: United Kingdom

    #2
    The boost dropping off is just the boost profile, it does not hold the same boost
    through the rev range, peak boost on a chipped car would be ~21 psi dropping
    off to ~11 psi at redline

    Comment

    • driftin jo
      S2Forum Fiend
      • Sep 2007
      • 2222
      • Country: United Kingdom

      #3
      If it's the top breather pipe on the back of the cam cover that is split then
      this will allow unmetered air into the inlet before the turbo after the MAF
      and would cause it to run lean so this could cause lean missfire under boost.

      Fix the leak first as you know it's there.

      Comment

      • Tonybolony
        S2Forum Maniac
        • Dec 2011
        • 636
        • Country: Wales

        #4
        Cheers Jo,
        2 interesting points there.
        Hoping to get pipe early next week.

        Comment

        • prj
          S2Forum Zealot
          • Mar 2010
          • 6308
          • Country: Estonia

          #5
          You have several issues.

          Boost leaks (pressure test the intake, you will have them for sure), as well as your plugs are bad or your coils are on the way out.
          http://tuner.ee - http://www.facebook.com/tuner.ee

          Comment

          • Tonybolony
            S2Forum Maniac
            • Dec 2011
            • 636
            • Country: Wales

            #6
            Originally posted by prj
            You have several issues.

            Boost leaks (pressure test the intake, you will have them for sure), as well as your plugs are bad or your coils are on the way out.
            Thanks PRJ,
            I know there have been some interesting discussions about which plugs for an ABY, but what would You use??

            Comment

            • prj
              S2Forum Zealot
              • Mar 2010
              • 6308
              • Country: Estonia

              #7
              NGK PFR7B on a standard engine.
              http://tuner.ee - http://www.facebook.com/tuner.ee

              Comment

              • UrS4boy
                S2Forum Obsessed
                • Feb 2006
                • 11859
                • Country: Canada

                #8
                One missing and hesitation diagnostic procedure

                You might want to read through this post (link below) and its internal hyperlinks:

                The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
                RS2'd 93 UrS4 5 spd sedan
                94 UrS4 V8 6 spd manual avant

                Comment

                • Tonybolony
                  S2Forum Maniac
                  • Dec 2011
                  • 636
                  • Country: Wales

                  #9
                  Originally posted by prj
                  NGK PFR7B on a standard engine.
                  Thanks,
                  Will get them tomorrow.

                  Comment

                  • stocious
                    S2Forum Maniac
                    • Jul 2012
                    • 838
                    • Country: Ireland

                    #10
                    My split breathers made a violent cut rather than a miss.. **** me pants when it happened lol.. Oil around the rear of block might be a giveaway!

                    Good luck with your search!
                    1991 S2 3B Coupe, KW v1, solid sub frames, poly bushed, chipped, about 260 ish

                    Comment

                    • Tonybolony
                      S2Forum Maniac
                      • Dec 2011
                      • 636
                      • Country: Wales

                      #11
                      Originally posted by stocious
                      My split breathers made a violent cut rather than a miss.. **** me pants when it happened lol.. Oil around the rear of block might be a giveaway!

                      Good luck with your search!
                      Yep, there is oil at back of head/block, which I assumed was leaking from the cam cover, and wasnt high on my list of priorities.
                      Sounds like it could be related tho.
                      When the new breather pipe arrives, I'll clean all the relevant pipework.

                      Comment

                      • UrS4boy
                        S2Forum Obsessed
                        • Feb 2006
                        • 11859
                        • Country: Canada

                        #12
                        Originally posted by Tonybolony
                        Yep, there is oil at back of head/block, which I assumed was leaking from the cam cover, and wasnt high on my list of priorities.
                        Sounds like it could be related tho. When the new breather pipe arrives, I'll clean all the relevant pipework.
                        Here is a photo of the "Item 7" 90 deg hose that connects the crankcase ventilation system to the pass-through tube in tha AAN/ABY/ADU cam cover. The OE rubber one has split. That is a $5 Chinese silicone hose that is going to replace it.





                        RS2'd 93 UrS4 5 spd sedan
                        94 UrS4 V8 6 spd manual avant

                        Comment

                        • Tonybolony
                          S2Forum Maniac
                          • Dec 2011
                          • 636
                          • Country: Wales

                          #13
                          That's the one!!
                          I ordered it with Pete R, and hopefully it'll be here in a few days.

                          Comment

                          • UrS4boy
                            S2Forum Obsessed
                            • Feb 2006
                            • 11859
                            • Country: Canada

                            #14
                            Originally posted by Tonybolony
                            That's the one!! I ordered it with Pete R, and hopefully it'll be here in a few days.
                            Post up a photo of the old split one when you get it off. (Please)
                            RS2'd 93 UrS4 5 spd sedan
                            94 UrS4 V8 6 spd manual avant

                            Comment

                            • Tonybolony
                              S2Forum Maniac
                              • Dec 2011
                              • 636
                              • Country: Wales

                              #15
                              Originally posted by UrS4boy
                              Post up a photo of the old split one when you get it off. (Please)
                              No prob, but it is split in exactly the same place as yours.
                              Jubilee clip overtightened??

                              Comment

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