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Hello everyone,

First of all, I'd like to excuse for creating another topic for 912 misfires, but I couldn't find anything that could help me in already existing topics.
I have a year 1999 912 ULS 100HP engine. A couple weeks ago I did the magneto check before take off and noticed vibrations on ignition contour B. Called my technical and he suggested to check ducati ignition modules. I swapped them around and indeed the problem went from ignition contour B to A, thus indicating that one of the ignition modules went bad. Technician suggested to replace both modules, but when I saw their price my jaw reached the floor... 😅. I did some research and found out that there is a Czech company called Ignitech making these ignition modules for motorcycles and they also do configuration and adapters for rotax 912/914 and each modules costs only ~150 euros. I've looked in the forums and in the internet and found out that these modules are indeed used across the world and there even is a company in UK that imports them and installs in ulta lights. So I've felt pretty confident and  bought 2 of these units and installed them on the firewall away from the heat and vibrations just as the manual suggested.

At first, everything looked fine, tests on the ground with low and high rpms went smoothly on each ignition contour. However, things started to go bad on flight. The same ignition contour B started randomly misfiring on RPM >=4000. At first I thought that one of the ignitech modules is faulty, but when I switched module A with module B, the problem stayed on the same contour B meaning that this is not the problem of the ignition module itself (probably). So, I've downloaded the rotax manual and went through the whole ignition system and checked the resistance of ignition coils (secondary and primary), trigger coils, charging coils and ignition caps. When engine is cold, all resistance values are in spec. When engine is hot, all resistances are also good expect for trigger coils which all rose up from ~240 to ~275 ohms but I somehow doubt that this is a problem. I have also replaced all spark plugs, checked the spark plug wires with a special tool and even trimmed their ends just to be sure. I've also used heat gun to heat up ignition coils and checked resistance again, all in spec. Sadly, nothing has changed, contour B still causes misfires with ignitech module.

Interestingly if I put my one good ducati module on contour B and ignitech module on contour A, engine starts to work properly on each ignition contour, no more misfires. If I swap ducati from B to A, misfires appear again. I have a thought that there might be a problem with my stator assembly (even though all resistance values are in spec) and that it might've cause a premature failure of my original ducati ignition module. Maybe these Ignitech modules are more sensitive to voltage changes or something and that causes misfires? Their manual states working voltage 8-18V and overvoltage protection kicks in from 20V. Interestingly, when I connect via serial cable to these ignitech modules and turn on the engine, their onboard voltmeter shows 18.5V and sometimes even 19.0V when RPM >= 1800. The voltages are the same on both A and B. 
How likely is that this voltage sometimes jumps above 20V and causes overvoltage protection to kick in on contour B causing those misfires ? (relating to that ignitech module sensitivity that I've talked above). Could it be that the problem here is actually the stator? From what I've heard they go bad really really rarely so I'm a bit skeptical about this.

Sorry for the wall of text but I'm really out of ideas and I'm hoping that some of you might have some suggestions for me. I've also written a letter to Ignitech but I've heard that their customer support ain't that great so I'm not expecting a reply from then anytime soon. 

P.S 
Those misfire happen only when flying and on land only after landing. 

  • Re: 912 ULS misfire on contour B

    by » 5 weeks ago


    Not sure if you checked this yet...  There is a propensity for the wires to crack.  For whatever reason, the Ducati boxes (SMD's) and trigger coil wire harnesses all use silicone wire.  Couple this with all the vibration and heat you get in an aviation environment.

    The silicone wrapping of the wire holds together so the wire can look okay on the outside.  Anyway, its another place for you to look.  In my case, it was the red charging coil wire that cracked near the faston connector.  I don't know why Rotax didn't require mil-spec wire for the ignition wiring harness.  A lot of times the cracked wire still conducts electricity, but probably not as much current or voltage.

    I doubt it is in the trigger or charging coils.

     


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