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Hello all

Any help/expertise/advice to assist with my problem would be greatly appreciated.

Rotax 912IS with Dynon Skyview: 300 hours.

No problems until recently when doing circuits and on climb-out Lane A solid warning light came on and  Dynon Skyview annunciation "Land Aircraft" appeared.  Didn't notice any roughness of engine operation at the time.   Landed and shut down.  

I have no access to a BUDS dongle.

Observations and investigations so far:

A. with both Lanes turned on and engine running: engine runs a little rough with cylinder 2 EGT rising immediately after starting, to reach approximately  170-200 F higher than the other three cylinders .  Neither Lane A or Lane B warning lights come on and there is no Dynon Skyview annunciation of engine alerts/faults.  If Lane A is turned off and Lane B remains on,  the engine changes from running a little rough to normal/smooth operation and cylinder number 2 EGT reduces to the same as the other three cylinders within 15-30 seconds.  If Lane B is turned off with Lane A remaining on, engine runs very roughly and cylinder# 2 EGT reduces quickly to zero. 

B. With engine running, both Lanes turned on and cylinder # 2 rear fuel injector electrical connection disconnected: solid Lane A warning light on, smooth running and equal EGT of all cylinders.  If Lane A is turned off there is no change of #2 cylinder EGT.  If Lane A is turned back on and then Lane B turned off # 2 cylinder EGT reduces to zero and engine runs very rough. 

D. fuel injector rail and injectors for cylinders 2 and 4 were removed and examined: resistance across terminals of all four injectors observed to be the same value using multi-meter and good spray pattern observed for each injector. 

E. If the motor is cranked over with both Lanes turned on and fuel pumps off with both # 2 cylinder  spark plugs removed and attached to high tension leads sparking is observed at the top spark plug but no sparking of the bottom spark plug.  New spark plugs were then connected to high tension leads and the test repeated.   Again no sparking of bottom spark plug was observed. When this test was repeated on #4 cylinder both spark plugs were observed to spark simultaneously.

F.  Disconnecting high tension lead from top spark plug of #2 cylinder and engine cranked over: engine didn't fire.

G.  Disconnecting high tension lead from bottom spark plug of # 2 cylinder: engine fires and runs as in A.

H. High tension lead exiting from top of Coil 1  ( labelled 'Coil 1T')  connects to bottom spark plug of cylinder #2. 

I.  Spade terminals of the each positive and negative low tension wire into all coils were examined.  They were all firm with no corrosion.  Resistance was tested across positive and negative terminals of all the coils tested using a multimeter and observed to be the same for all coils.

J. Two new spark plugs were tried in # 2 cylinder simultaneously and made no difference.

My conclusion is there is an electrical problem resulting in no/poor spark at bottom spark plug of # 2 cylinder, but I have not isolated the cause.  A new spark plug has been tried without benefit.  The resistance between the positive and negative low tension terminals of Coil 1T is observed to be the same as the other Coils ( however I don't know if this is a valid test for testing the integrity of the coil). 

Thanks

George  

 

 

 

  • Re: Rough running/High EGT in Cylinder 2

    by » 3 months ago


    I assume you checked for corrosion in the 2B spark plug connector.  You could try swapping ignition coils to see if the problem follows the coil?


  • Re: Rough running/High EGT in Cylinder 2

    by » 3 months ago


    I agree with Jon!

    The spark plug connector Cap just unscrews from the wire.  Lefty Loosey!

    If you have the slack, cut 1-2 wire diameters off the end of the wire and screw the cap back on.

    A small amount of Silicon Grease applied to the cut end won't hurt either.

     

    The 2B plug fires at the same time as the 1T plug.

    If the 2B is dead so is the 1T, Unless...

    The 2B is sparking somewhere other than at the spark plug electrodes.

    Check the 2B wiring for chaffing.  Is it rubbing anywhere?

    Measure the resistance from the 2B spark plug connector to the 1T connector.

    Expect to see 15-20,000 ohms.

    Measuring from either connector to ground should read as an open circuit. (>10 Million ohms) 

     

    Viewing the running engine in a Dark (Really Dark!) location can reveal blue sparks coming from places they should not be coming from.

    Exercise extreme caution when near a running engine, especially in the dark.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Rough running/High EGT in Cylinder 2

    by » 3 months ago


    According to the MM the #1 coil also fires 1B spark plug.  But you aren't having any problems with the #1 cylinder so it sort of points to the 2B/1T cable as Bill has suggested.  Did you check the connection at 1T also for corrosion?


  • Re: Rough running/High EGT in Cylinder 2

    by » 3 months ago


    Maybe you could pull the 2B and 1B spark plugs and switch the cables at 1T and 1B on the coil and then crank.  That should tell you whether it is the cable or the coil? If the 2B spark plug still doesn't fire, then it is the cable. And if the coil is OK, the 1B spark plug should still fire.  Assuming my logic is correct?


  • Re: Rough running/High EGT in Cylinder 2

    by » 3 months ago


    Thanks very much John and Bill for your thoughts.

    Bill:  You wrote ' The 2B plug fires at the same time as the 1T plug.'   On my engine the high tension lead from the bottom of Coil 1 is connected to bottom spark plug of cylinder 1, so I believe Jon is correct when he wrote 'According to the MM the #1 coil also fires 1B spark plug'.

    There was no corrosion at 2B spark plug connector and also where the high tension lead 1T screws into Coil 1.  I did remove spark plug connector of 2B lead,  cut 10 mm off the end and rescrew the spark plug connector on.  This did not produce any change.

    Swapping Coil 1 with another appears to be a challenge (involving disconnecting transverse fuel rail to remove Coil1, and disconnecting four high tension leads from two coils to swap them over, so I will try to avoid this if possible).

    Before I go further I best first check my understanding of some fundamentals of this engine are correct;

    Can you please confirm that the following statements reflecting my current understanding are correct  (and excuse me for any naivety);

    1.  The two fuel injectors to each cylinder do not discharge simultaneously during each cycle during normal operation.  One of the injectors fires on one cycle and the adjacent injector fires on the next cycle.   ie each injector discharges every alternate cycle

    2. Both spark plugs in each cylinder fire simultaneously during each cycle during normal operation with both Lane A and Lane B are turned on. If one of the Lanes is turned off or suffers a critical failure, the other Lane ensures that both spark plugs in each cylinder continue to fire simultaneously during each cycle. 

    3.  There is one coil enclosed within each of the four coil bodies, and not two. This single coil is connected to both high tension leads exiting the coil, and is responsible for firing both of those high tension leads simultaneously.   If there was a problem with the coil this would result in a problem with one spark plug in two cylinders, and cause observable changes in two cylinders.

     

    If my understanding at 3. is correct and in my case a problem is within Coil 1, then I would expect to be observing raised EGT's in both cylinders 1 and 2 caused by failure of both 2B and 1B spark plugs (which I am not).

     

    Thanks.

    George


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