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AAN in T3 Syncro 16 - misfire above 10psi boost

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  • AAN in T3 Syncro 16 - misfire above 10psi boost

    Well I've finally managed to get my AAN boosting properly by replacing the MFTS.

    The engine is standard other than an air filter cone and a one off exhaust system (runs a standard downpipe which then splits into two 2 1/2 inch pipes with one silencer each and the ECU has a chip and external 3bar MAP sensor.

    I've only been making use of the boost (goes up to 22-23psi / 1.5 bar) for around a week when suddenly yesterday it would only boost to 15psi and then kangaroo like crazy. I turned off/on and the fault cleared. Plugging in with Vag-com showed that it had overboosted (00544 Maximum boost exceeded). Should I have changed a boost sensor when fitting the chipped ECU?

    This morning, it started misfiring at anything over 10psi. It runs smoothly otherwise, idles smoothly, pulls well up to 10psi but 'flutters / misfires' if you try to push it above this.

    I've just checked the fuel pressure and when running I have 57-58psi. Once turned off, it drops to 49-50psi. I left it for around 25-30 minutes and it didn't lose any pressure. That said, when I first disconnected the fuel pipe to fit the T-piece, there was a fair amount of air in the fuel line, not just fuel. More about this in a moment.

    I've pulled the plugs out and they all look good, light grey. They're Bosch FR5DTC and have only done 2-3,000 miles.

    I'm running the standard injectors, coils etc.

    When checking the plugs, coils and coil tubes, I had a quick look at the wiring etc. Everything looks fine.

    Any ideas as to where to start?

    One other fault to work out. The engine does not want to start when hot. I know that this is a separate fault as this has been an issue ever since I installed the engine. I wonder if the fuel is getting hot enough to boil off creating a lack of fuel. It takes a good 30 seconds of cranking before the engine fires and then it won't idle. It takes a few minutes of driving before it returns to normal. I haven't had a chance to test the fuel pressure while it won't start. I think I'll need a remote fuel pressure gauge for this. Anything obvious?

    Thanks in advance.

    MG

  • #2
    MAF sensor broke?
    boost leak somewhere?
    audi coupe quattro b2 2.2 20vt project (573hp-626nm)
    TWINCHARGED power,zero lag
    AEM W/M injection

    Comment


    • #3
      Originally posted by quattro-nick View Post
      MAF sensor broke?
      boost leak somewhere?
      Hmmm, no faults re MAF but boost leak I guess? Would that give a flutter/misfire type roughness through the car? Or would it just not get full boost?

      MG

      Comment


      • #4
        you can check boost pressure in vagcom while your driving
        is the little boost hose still on the AAN motronic ecu?
        audi coupe quattro b2 2.2 20vt project (573hp-626nm)
        TWINCHARGED power,zero lag
        AEM W/M injection

        Comment


        • #5
          Originally posted by quattro-nick View Post
          you can check boost pressure in vagcom while your driving
          is the little boost hose still on the AAN motronic ecu?
          Really? The only measuring block with regard to pressure I could find was just normal pressure. Not boost. Which block?

          MG
          Last edited by RS2; 23rd October 2015, 19:26.

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          • #6
            One Missing and Hesitation Diagnostic with links

            Have a read through this:

            One Missing and Hesitation Diagnostic with links:

            http://forums.quattroworld.com/s4s6/msgs/22611.phtml

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

            Comment


            • #7
              Do a pressure test, you almost certainly have a leak.

              If not it will be the MAF or MAF connector.

              Try unplugging and replugging the MAF a few times to clean the contacts and see if it runs better.

              S2 Coupe 3B Project


              Ur quattro restoration

              S2 Avant

              Boost is the new rock and roll!
              sigpic

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              • #8
                I think I've found the issue as a boost pipe clip.

                I'll find out tomorrow on the way to work.

                Thank you all

                MG

                Comment


                • #9
                  Well... that didn't fix it! I found a boost clip that had slipped off allowing boost to escape.

                  A question... if it's a misfire, would the boost still climb as normal but obviously the engine be down on power?

                  I think I need a spare coil and Ignition Module to swap out...

                  MG

                  Comment


                  • #10
                    OK so there was a boost leak... which is now fixed (it boosts beyond 15psi even with mis-fire - no I'm not doing this regularly!) but the misfire is still there.

                    I expect that the coils, wiring and connection tubes are the factory units and are probably not coping well with 22-23psi boost upgrade.

                    I've started looking into replacing the entire ignition system with a modern upgrade. There are many companies offering conversion kits but which is good? bad? easy to install? etc

                    Thanks

                    MG

                    Comment


                    • #11
                      Easiest conversion is with 2.0 TFSI coils and a pre-made harness. There are folks who make these harnesses here and they are also available on eBay (no guarantee on quality).

                      Or just purchase a complete kit from EFI Express. Plug and play. 20 minutes. Done.

                      http://www.efiexpress.com/catalog/pr...products_id=66

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

                      Comment


                      • #12
                        Thanks.

                        I've put up a wanted ad for a loom kit.

                        If anyone reading this makes a loom kit, please get in touch.

                        MG

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                        • #13
                          Update time.

                          I've been trying out a modern setup of TFSI coil packs and a conversion loom from another S2 member (who knows his stuff, I trust his workmanship) with the following results.

                          First fit of the loom and TFSI coils resulted in a permanent misfire on cylinder 4! It would not clear. This was done fairly late in the evening so I couldn't spend time swapping parts over to see what would clear the misfire. I could only put the standard setup back on for driving to work again the next day.

                          I then bought a set of NGK BKR7EIX plugs and fitted them. I didn't gap them as the boxes indicated that it should not be done.

                          Just fitting the plugs made a difference. With the standard coil setup, the idle is smoother and the misfire now only kicks in above 15psi boost.

                          A week later (I've been ill so no time to play with it), I managed to try the the TFSI setup again.

                          In the process, I also gapped the plugs down to 0.6mm (this was recommended to me by the same person who has built the TFSI conversion loom for me) and fitted the TFSI setup again.

                          This time, at idle all is smooth. However once out on the road, anything above 3-4psi and it's misfiring again. Once warmed up, it's even misfiring at low rpms with the foot down (i.e. barely any boost).

                          So back to the standard coil setup again and with the plugs gapped at 0.6mm, I can now get to 18psi without it misfiring.

                          To me, this proves that it's definitely an ignition fault and that the standard setup is giving the spark plugs a much better spark than the TFSI setup... but I still have no idea why I'm getting the misfire under boost.

                          Any ideas?

                          MG

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                          • #14
                            maybe a problem with ignition timing ?
                            how is your crankshaft sensor and camshaft sensor
                            check also your fuel pressure
                            audi coupe quattro b2 2.2 20vt project (573hp-626nm)
                            TWINCHARGED power,zero lag
                            AEM W/M injection

                            Comment


                            • #15
                              Fuel pressure was checked before I started all of this. It's within spec and holds pressure.

                              I'll look at camshaft/crank sensors.

                              I would've thought that they would throw fault codes though?

                              I'll plug in tomorrow on the way to work and see if there are any codes.

                              These engines are great... apart from when they're going wrong and you realise that the early OBD2 diagnostics aren't very specific.

                              MG

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