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  • Engine missfire

    I have a problem with my Rotax 912, it has an intermittent miss, I have narrowed it down to electrical.
    I was told it could be a spark plug breaking down so I changed them out and flew for one hour this time without a miss.
    One week later I flew for another hour and in the first 30 minutes I had 4 misses.

    The miss is a bump that can be felt through the machine, a Xenon RST, for the next 30 minutes I had no bumps.
    I fear the bump could get worse and eventually cause a total engine failure.
    I have this magnificent machine but I have no confidence in flying it anywhere.
    I hope someone can offer some ideas of what may be the cause of this engine miss.

    Baz.

  • #2
    How did you narrow it down to an electrical issue? I have an occasionally run-running engine, but it is a carburetor issue (AFAIK).
    Do you have EGT gauges? What does the EGT do during the mis-fire episodes? Check for a loose ground wire?
    Brian

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    • #3
      You are aware that this is an international forum with members from all over the planet? I'll start out by saying that I guess you only want help from someone who already knows everything about you. But that's not true is it? If that were true, you'd have Private Messaged them.

      Right now, all I know about you is that you live somewhere around a place called Coffin Harbor, wherever that is.

      So, let's start over with some details: Exact location of where you fly out of(North or South of the Earths equator), weather in that area for the past 2 weeks, you know, temps, rain, snow, sleet, that stuff. Age of your gyro, age of its engine in hours. Date of last A&P inspection, age, quantity and type of fuel used, compression of each cylinder, hot with throttle wide open, ignition disconnected, number and type of magnetos and age, age of ignition battery, date in logbook of when all the ignition wiring was continuity checked, hours in the logbook since last oil change, type of oil used, date in logbook since the fuel system was last flushed, and filters replaced.


      Regards

      Frank

      Comment


      • #4
        Originally posted by eutrophicated1 View Post
        You are aware that this is an international forum with members from all over the planet? I'll start out by saying that I guess you only want help from someone who already knows everything about you. But that's not true is it? If that were true, you'd have Private Messaged them.

        Right now, all I know about you is that you live somewhere around a place called Coffin Harbor, wherever that is.

        So, let's start over with some details: Exact location of where you fly out of(North or South of the Earths equator), weather in that area for the past 2 weeks, you know, temps, rain, snow, sleet, that stuff. Age of your gyro, age of its engine in hours. Date of last A&P inspection, age, quantity and type of fuel used, compression of each cylinder, hot with throttle wide open, ignition disconnected, number and type of magnetos and age, age of ignition battery, date in logbook of when all the ignition wiring was continuity checked, hours in the logbook since last oil change, type of oil used, date in logbook since the fuel system was last flushed, and filters replaced.

        My name is George Jacob, sometimes called Jake, most of the time called A$$ HOLE.
        I live in a secluded area with no neighbors, rain or snow.
        I am an inventor and designer of All my gyroplane needs.
        I've never changed my oil and all my wires are exposed so I could see the uninsulated crimps.
        I don't have a log book and fly frequently.
        So, are ya gonna help the guy or try and take my job as a Smart A$$
        Since this is an international forum, you just became an international WEENIE
        I'm sorry not to bring rational input, but I know nothing about Rotax 4 cycles.


        Life,The leading cause of Death

        Live and Learn--OR--Die and be an example

        321.252.7705

        Comment


        • #5
          I wouldn't think of taking your job, Jake, or shall I say, your supreme weenie Highness. And after 45 years of trying to help people diagnose their rough idles, and misfires, I think I'm entitled to be a little grumpy, when pleading for a modicum of information. But you go ahead, Jake, I forgot my swami-turban today; you go ahead and help him.
          Regards

          Frank

          Comment


          • #6
            Iíll start by suggesting you also try Rotax-Owners.com and speak with a local Rotax service mechanic.

            One thing that is unique about your engine is the factory changes (unless Iím misinformed). They put a third party turbo on the 912UL (80hp) to put out 135hp. They do not weld the pressed cranks from my understanding so there is a potential for more complex issues with this motor than a typical 912 or 914 (but doubt that has anything to do with this issue, if I had to guess Iíd look at the carb floats first).

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            • #7
              I live in Australia, somewhere around a place called Coffs Harbour if that has anything to do with the problem.
              The fuel system has been checked out which is why I think it's an electrical problem as it is an intermittent misfire.
              The engine has 150 hours on it and it is serviced every 50 hours.
              I just thought someone out there may have experienced a similar problem.
              Sorry to have bothered you so much.

              Comment


              • #8
                Originally posted by eutrophicated1 View Post
                I wouldn't think of taking your job, Jake, or shall I say, your supreme weenie Highness. And after 45 years of trying to help people diagnose their rough idles, and misfires, I think I'm entitled to be a little grumpy, when pleading for a modicum of information. But you go ahead, Jake, I forgot my swami-turban today; you go ahead and help him.
                And don't you forget it !! :) :) : )
                Life,The leading cause of Death

                Live and Learn--OR--Die and be an example

                321.252.7705

                Comment


                • #9
                  If new plugs fixed it temporally the miss could well be something in the ignition. Coil and ignition wires come to mind as well as the box that tells the plugs when to fire.

                  I have no engine experience with the Xenon.

                  The Rotax 914 has a lot of complex electronics that can prove problematic.

                  I could also be a problem with the floats or a sticking waste gate.

                  A better description of the bump might help people help you.

                  Having a qualified person look at the plugs you removed may help you to learn something.

                  What the manifold pressure does during the bump could also be helpful in diagnosing the problem.

                  In my opinion your Xenon is not airworthy till you fix the problem because I agree; it will likely get to be a bigger bump one day leading to an unplanned landing.
                  Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                  Comment


                  • #10
                    See Vance, that's why you're Awesome.
                    You might not know the definitive answer, but you do see the big picture that may narrow down the symptomatic problems.
                    Life,The leading cause of Death

                    Live and Learn--OR--Die and be an example

                    321.252.7705

                    Comment


                    • #11
                      I fly a Xenon also and had a similar problem but my problem - and possibly yours -- was not Xenon specific. I had the exact same issue as you did with intermittent misses - changing the spark plug fixed it - temporarily. Finally it got bad enough that I as able to diagnose it ---- There was a hairline crack in the insulation of several spark plugs- it was the same on several plugs. When I changed plugs and I got it again I took a magnifying glass to all the plugs --- I had bought a whole box of plugs - and even the unused ones from the box had cracks. I'm guessing that the box must have been dropped or something and a bunch of the insulators got cracks. Once they started arcing it got worse and worse.

                      Good luck.

                      Rob
                      Rob Dubin

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                      • #12
                        Thanks Rob, the bump happens too quick to see what is happening with manifold pressure or any other gauges, I'll be having the black boxes tested and checking the plugs for cracks.
                        Baz

                        Comment


                        • #13

                          i had this problem and it was of the spark plugs, change it and see that it has another manufacturing number. Sometimes come all the bad lot.

                          Comment


                          • #14
                            What are the spark plugs that are being used ?

                            Just curious as this might be something to keep in mind if it happens to me.

                            I would have never thought to look at the new plugs as being the problem !!

                            Thanks for the info Rob.
                            Best Regards,
                            Eddie Sigman,Polvadera,nm
                            (575) 835-4921

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