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Ignition module won't shut off

  • Eric Goethel
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5 years 2 days ago #4642 by Eric Goethel
Eric Goethel created the topic: Ignition module won't shut off
I have an intermittent problem with one of the ignition modules on my 912. Sometimes it will shut off normally and other times I get no drop on run up and I can only shut the engine down by turning off the fuel supply. I've disconnected the ignition switch wire at the ignition module and I get a good ground through the switch. I've also pull tested the wire from the ignition module to the connector and it does not seem to stretch. I guess my next step is to replace the wire connector and, if this doesn't work, to send the ignition module out for bench testing. Has anyone seen a failure like this or have any suggestions? It's a little frustrating trying to trouble shoot this problem since it happens so infrequently.

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5 years 7 hours ago #4652 by Kevin Stewart
Kevin Stewart replied the topic: Ignition module won't shut off
Hi,

Here's a thought on how you could diagnose where the break lies.

  1. Connect a resistance meter (multimeter) between ground and the WORKING ignition wire on the back of the ignition switch.
  2. Measure the resistance. This is your reference of what you should measure on the NON-WORKING side.
  3. Do the same on the other side and pull/poke the wire and connectors all the way back to the ignition module until you determine where the break lies.

  4. This should be cheaper than just changing parts until the fault goes.

    Kevin

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2 months 2 weeks ago #16871 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
I am experienced with the Rotax 912/914 engines. I have received maintenance training up to Heavy Maintenance. But, I do have a problem that I cannot resolve. The engine is mounted on a motor glider and during flight we routinely shut down the engine. For reasons unknown the engine will not come to a complete stoppage as it always has done in the past. Normally the propeller stops turning, and then the propeller is feathered. That normal action was routine for 250 hours on a regular bases with this aircraft. Upon shutting off the rotary switch (off, L,R, Both, Start) to off and while throttle is set to idle position, the engine continues to run, but hesitant, some roughness, partially firing and it sounds and feels like it is dieseling or something. It's certainly not smooth and not normal. If you put the ignition back to both, the engine sounds change to instantly smooth running at idle. I don't dare allow the engine to run any more than a few seconds before switching it back on. We changed out the ignition switch with a new one, no improvement. But look at a little history now.

This condition has occurred on two separate occasions about a year apart. The first occasion we investigated the P-leads to the ignition modules to make sure they were making ground when the ignition switch was turned off, and open when they were turned on. I proved the ground contact was made and it should have shut off the ignition modules. The connectors at the modules were also examined and they were found to be okay, at the six pin plugs at the modules themselves. If the ground leads were open then the ignition modules are alive. I must add too, that upon landing and shutting off the engine it would sometimes shut off by turning the ignition switches off, but sometimes it was necessary to turn off the fuel to get it to shut down while on the ground. Shutting down on the ground was inconsistent. We had new ignition modules available so we put on new ignition modules. That did not change any of the characteristics. So we traced the ignition grounding wires from both ignition modules to the switch. There we found embedded wrapped in black tape on the ignition ground wires a diode in each one of the wires grounding the ignition modules. Okay, those were removed and the wires were connected direct. We called everyone we knew to see why there would be diodes in those wires. A diode is a one way valve for electrical circuits. That circuit should be only either open or closed, doesn't need diodes. Open to operate and closed to shut down. Wah-la, that fixed it. The engine would then shut down in flight, feather the prop, shut down upon landing worked just like it was supposed to do all along. It worked fine for nearly a year.

Second occasion, it’s now doing it again. It want shut down completely in flight, it runs like its dieseling not good. I does shut down on the ground by turning off the ignition modules. Sooo, while in flight there is forward motion at nearly stall speed and that seems to be enough to keep wind milling the propeller, and enough turning of the engine to keep it running. Normally at 60 knots the propeller will stop turning when shut off on all other Lambadas and SunDancers that I have flown equipped the same as this one.

So one may conclude that the turning of the propeller (wind milling) causes the vacuum or movement of air through the carburetor sucking fuel into the venture allowing fuel into the cylinders, and the fuel is igniting from pressure, like a diesel, or maybe hot clinkers inside the cylinder heads. The owner does run 91 octane mo-gas nearly 100 percent of the time. The owner did run 100 LL for a while thinking that he could clean up the clinkers if there were any. The spark plugs are clean with maybe 50 hours on them.

I flew this Lambada just last May 2017 and everything was fine. You could stop the engine, feather the propeller normally, and restart normally. Out of the blue it is doing the same thing all over again, except the engine will shut off normally on the ground.

I will appreciate any ideas that anyone may have. You can contact me at my cell phone: 559-960-7873 or my email address at: joekulbeth.airusa@gmail.com

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  • Roger Lee
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2 months 2 weeks ago #16874 by Roger Lee
Roger Lee replied the topic: Ignition module won't shut off
Sounds like you have a bad ground. Check the screw tightness on the back of your rotary switch. Make sure the grounds out by the ignition modules are tight to.
Going to fast in flight and trying to get the prop to stop at times can be just a matter of speed. After tightening the grounds try slowing down more if you are at a higher speed than before.

p.s.
All grounds may be hand tight, but wrench loose. Put a wrench on all of them and don't just wiggle them.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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2 months 2 weeks ago #16875 by Bill Hertzel
Bill Hertzel replied the topic: Ignition module won't shut off
It sounds like you have a little carbon in there, Clinkers!
Do you go from full power to shut down without a cooling period?
Either way, change the procedure!

The next time it happens in flight, Engage the Choke and open the throttle.
That may be all it needs to snuff out the Clinkers.
If it revs up, report back here.

Or just feather the prop.
The windmilling prop may add enough energy to keep it going where the dieseling alone would not.
The engine may be loosening up in its middle age, making the windmilling easier.

Essentially, whatever you are now doing, try something different.

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2 months 1 week ago #16877 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
Thanks for the info, but I have pulled the engine up to a full stall. So much so that it went into a spin. The engine will still run. I cannot feather the prop without a dead engine as it is a carbon fiber prop and while I know it is very strong, it will break if subjected to that type of stress. The engine will shut down on the ground with no problem. I will try and kill it with the choke and see what happens.

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2 months 1 week ago #16881 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
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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2 months 1 week ago #16885 by Bill Hertzel
Bill Hertzel replied the topic: Ignition module won't shut off
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!

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2 months 1 week ago #16891 by Alan Arnold
Alan Arnold replied the topic: Ignition module won't shut off
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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2 months 1 week ago #16893 by Bill Hertzel
Bill Hertzel replied the topic: Ignition module won't shut off
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.

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2 months 1 week ago #16896 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
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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2 months 1 week ago #16897 by Alan Arnold
Alan Arnold replied the topic: Ignition module won't shut off
The water/steam treatment has the advantage of not adding hydrocarbons to the area that you wish to remove the burnt on hydrocarbons from. The question is, is it too harsh for the Rotax.

Alan

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2 months 1 week ago #16931 by Bill Hertzel
Bill Hertzel replied the topic: Ignition module won't shut off
Just watched a couple of You Tube Videos of the Water and Seafoam treatments.
Neither of them worked worth a hoot. Snake-Oil.!

Another thread reminded me to remind you to check that the spark plugs have Heatsink compound, and NOT Anti-Seize!, on the plugs.
Without the heatsink compound, the plugs will run much hotter and may act like a glow plug keeping the engine running.

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2 months 1 week ago #16936 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
I kinda thought about that and it to is snake oil treatment, I would only do something like to an old Ford or Chevy inline six around the mid term of last century just to see if there was something to it. I do us each and every time the heat sink. I think if is very important to apply it.

I will not have time for a long while to pursue this repair, but I sure have gained lots of insight from all of the people that has become interested in my problem. I will let everyone know how it turns out when I get done with it.
The following user(s) said Thank You: RotaxOwner Admin

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3 weeks 1 day ago #17382 by Thomas Wirl
Thomas Wirl replied the topic: Ignition module won't shut off
Hi, we had a similar problem in a motor glider.
As it looks the mixture was too fat and coal was building up on the spark plug or the cylinder.
Finally we had the carbs overhauled and the problem was gone. Also the floats had overweight.

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2 weeks 5 days ago #17419 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
I think the last blogger got it right this time when he said they over hauled the carbs and the problem went away. He see above where he mentioned the floats were heavy, meaning they where sinking down into the fuel bowl and not shutting off the fuel completely. My conclusion is below.

Soooo, it the floats were heavy and sinking in the fuel bowl, that would allow the needle valve to come unseated and allow fuel to flow out of the fuel bowl. With the engine turning and the floats working properly (floats floating to the top of the fuel level in the bowl) would close off the outlet and not allow fuel flow to the cylinders, the engine stops. The propeller is turning, the pistons are going up and down causing air to be drawn through the ventura of the carburetor, creating a low pressure area in the carburetor, and the floats NOT seating and closing off the outlet, then fuel is free to pass onto and into the cylinders where it is hot enough to cause that type of explosion like dieseling when the ignition modules are turned off.

Joe Kulbeth Fresno, CA.

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  • Roger Lee
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2 weeks 4 days ago - 2 weeks 3 days ago #17422 by Roger Lee
Roger Lee replied the topic: Ignition module won't shut off
Hi Joe,
That theory won't work. When owners pull the throttle back the carbs still get fuel because they are set to idle somewhere between 1600-1900 rpm so they will always get fuel.
When the ignition is shut down there is no electrical impulse to fire the modules and no energy to the coils and then the plugs. No fire and it's not going to run. Cylinders are not that hot to auto ignite the fuel or you'd have a issue under normal running for all owners.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell
Last Edit: 2 weeks 3 days ago by Roger Lee.

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2 weeks 3 days ago #17431 by Joe Kulbeth
Joe Kulbeth replied the topic: Ignition module won't shut off
Roger I appreciate your input very much. I am still trying to wrap my brain around why this engine will not shut off in flight. For the last couple of flight it will not shut off on the ground after landing as well. The fuel has to be cut off and allow the fuel to run out of the carburetors before it will stop.

But the theory that the carburetor floats at least one of them maybe be heavy and allow greater than idle fuel amounts to pass into the combustion chamber still make sense to me. I don't know your experience in flying motor gliders, where ones flies to altitude and shut down the engine and then feature the propeller. Normally one slows down the aircraft to below 60kts, turn off the modules, and the propeller slows to a stop, feather the propeller and soar or glide around awhile. However there is still airspeed that causes the propeller to windmill and assist the continued turning of the pistons. With the windmill effect and any combustion taking place the engine continues to run, very uneven, but running never the less.

Assuming that the modules or properly grounded, and or in fact shut off and not producing any spark to the plugs. If a float or floats are heavy and allowing the needle valve to bypass more fuel than it would allow at the normal idle setting, then fuel entering the hot chamber, I think would have a tendency to ignite. I have personally experienced the phenomenon myself in the aircraft in question. We are going to do the carburetor overhauls to see, they are do for overhaul anyway. But thanks again Roger, and if you have more please by all means, say it out loud so we can all hear it. Joe

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2 weeks 3 days ago - 2 weeks 3 days ago #17433 by Bill Hertzel
Bill Hertzel replied the topic: Ignition module won't shut off
The Floats do not control the amount of fuel entering the carburetor proper.
They control the amount of fuel entering the float bowls.
The Jets and Needles control the amount of fuel Exiting the float bowls and enter the air stream.

The float level in the carb bowls has a minor effect on the richness of the mixture.
As you know, shutting off the fuel to the carbs does not instantly stop the engine.
It takes a while for the fuel level in the carb bowls to drop low enough for the engine to stop.
As the level drops, the engine continues to operate normally for quite some time.

Heavy Floats will only raise the level of the fuel in the bowls a small amount.
If the floats were so heavy as to not allow the float valves to close, the carbs would be overflowing onto the ground.

The carburetor and floats are not the root cause of the issue.
A rich mixture may be causing carbon buildup, but the rich mixture is not causing the dieseling.

The engine operates normally with the ignitions switches ON.
When the switches are turned OFF, the engine diesels-on running roughly.
This confirms that the plugs stopped firing with the switches OFF.
If the switches were actually ON, the engine would continue running like they were ON.
You would not see any change when operating the switches.

If you have some hot carbon spots in one or more cylinders, dieseling occurs.
The hot carbon is there during normal operation.
It does not cause any problems because the spark plugs normally fire well before Top Dead Center (TDC) where the compression is highest and the likelihood of dieseling will occur.
Buy the time the hot carbon would ignite the fuel, it is already burning. No problem.

When the ignition is shut off, the carbon clinkers get their chance.
The piston continues to compress the fuel load up to TDC where the clinker is able to ignite it.
It is Too little, Too late. You get a weak ignition that may still be burning when the exhaust valve opens and produces an extra loud bang in the exhaust.
This is not happening in all four cylinders. It may only be one, which is why the engine runs so roughly and weakly.
Overall the engine runs rough, loud and weak.
Last Edit: 2 weeks 3 days ago by Bill Hertzel.

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