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Ignition module won't shut off

in 912 / 914 Technical Questions 11 years ago

  • Re: Ignition module won't shut off

    by » 7 years ago

    I just cannot see what difference there is between shutting down an engine in flight as to shutting down the engine setting on the ground. All the time in the past to include about 250 hours of operation time, shutting the engine down in flight hundreds of times and the prop stops at about 55 knot airspeed. That has been routine and usual. But the engine seems to continue to run erratic like, like its dieseling. I feel certain that the P-leads are doing their job and the ignition modules are grounded with the switch is off. That is proven each time the engine is turned off while on the ground. So I think now there is something to the hot clinkers in the cylinders at least one or more of them, with the prop still turning the pistons are still drawing in fuel air mixture, but the spark timing such as the modules perform is not present, and maybe the clinkers is causing erratic combustion to take place.

    My biggest questions now, 1. has anyone else ever experienced such a thing? 2. does anyone have any suggestions as to who to talk to about this from Rotax?
      
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  • Re: Ignition module won't shut off

    by » 7 years ago

    I have had auto engine diesel-on back when cars had carburetors.
    Usually stepping on the gas killed the dieselizing.

    It is time to see what is really going on in there.
    If you do not have a bore scope, pull both plugs, shine a flashlight in the lower plug hole while looking in the upper.
    Rotate the engine until the piston face comes into view.
    If the piston is black, try spraying "Seafoam" or another "Top End Cleaner" in the cylinder. Let it soak for few hours and then repeat.
    When you first restart it, be sure to do it outside. It will smoke for about 20 seconds like you are an airshow performer!

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Ignition module won't shut off

    by » 7 years ago

    I don't know how you Rotax experts will react to this but, back in the ancient times, you know, the 60s and 70s, when we had that dieseling problem we would rev the engine up some and spray a few brief bursts of water into the carb throat. The small amount of water would explode into steam and thoroughly clean the entire combustion chamber.

    Whether this is a good idea with the Rotax is open for discussion.

    Alan
      
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  • Re: Ignition module won't shut off

    by » 7 years ago

    Alan,
    You're a braver man than I am!
    I was going to suggest the good old water treatment but feared I would get flamed.
    Seafoam is considered to be a "Snake-Oil" treatment to many.
    But there is little to lose if applied while the engine was not running at the time.

    I remember pouring a bottle of Bardahl down a carb once. The smoke was impressive!
    If the water treatment sounds too radical, a pint of diesel/kerosene has about the same effect.

    But he first needs to get a look at the pistons to see if carbon is a possible cause.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Ignition module won't shut off

    by » 7 years ago

    Obviously age and experience is what these blogs are about. Water in the carburetor to create a steam cleaning of the cylinder? I never tried that, and probably want. If there is a cleaning necessary, its not that much trouble to remove the cylinder head and clean them and reinstall. If just that making that determination as necessary. From this blog I have concluded two thing to try first.

    1. Fly the aircraft to altitude, and try to shut down the engine normally, have the EFIS page for the engine temps up and ready. Shut down the engine and if it still dieseling or continuing to run, check to see which cylinder or cylinders has the hot EGT, if any, Then increase the throttle to request more power which would supply more fuel to the cylinders, hopefully cold and wet, and maybe it would stop the engine. Just a thought.
      
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