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Rotax 912 Ignition Problems.

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Dan I know you have done a lot of checks as per emails. M61A1  Mick has posted his issue...this is more than likely similar to yours. This would certainly give you the symptoms you are seeing. Do the test with the multimeter on AC volts on the red wires this will confirm you are getting power or not and you dont need to pull the engine out


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Dan To help you with this I went to the hangar this morning and I did some measurements on my test rig for the voltages coming from the CDI coils in the stator. The measurements are engine RPM th

This is the sort of damage I found after stripping back the conduit which had no visible damage. Very similar symptoms....Working just fine the wouldn't start one day. No spark. Changed modules..

Waraton - you might like to check out the thread below. You can buy all types of connectors (plugs and spades and bayonet connectors) from Alanco or Ashdown-Ingram.   That means you basicall

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WOW!  I think we're ready to ask NetFlix or Prime Video to produce series for us!   So much to talk about.  So little time.    😃


Bob - your last post describes the perfect scenario for instantaneous failure in both ignition systems - shorting across the two charging coil leads - the exact reason for the Rotax SB 912-026 in December of 1999.    My first "test" at the hangar will be a close look inside the wire mesh sheath over the charging coil wires ...followed by checking the resistance between the connectors of the two "red" leads.   And, if the stator were never replaced, my engine has had 23 years reach the point of collapse.


Then I'll look for a squirrel in the exhaust pipe.


Mark: if it weren't for Wikipedia I'd still be hung up on CRO    but I'm still trying to get my head around:     the square Root of the Mean of the Square.  I get over my head quickly with electronics.  Fortunately, I had no problem with the chart of multimeter AC Voltage vs RPM from  Blueadventures - which was essentially confirmed by you. 


Thanks to all...keep safe,  fly safely.    I'll post my findings.     (JG - this was your thread......still reading?)




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Dan the quickest and easiest way to confirm there is something wrong with the charge coils for the CDI or a issue with shorting inside the harness is to use a multimeter and do the test for voltage as you spin the engine over with the starter..this will at least give you some better direction to look at



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Well. gentlemen; I have a plan for arrival at my hangar sometime this week.

Below is a summary of some of your suggestions and my additions, deletions and thoughts regarding what to expect. 

Should you notice flaws in my reasoning (...my wife tells me from time to time that this is possible...) please jump in.

Once I've completed the "trials", I'll update you all here.

As you will probably notice; I am leaning heavily towards "stator failure" as the culprit with my engine and may be looking for a good used P/N 996 539   or     P/N 888 675.

Stay safe. Fly Safely.



Engine checks in search of the cause(s) of sudden engine stoppage.

 NOTES:  Mag switches were checked for proper operation.

              Fuel system was checked for quality, supply and flow control; carb bowls properly full.

             The result of any test may preclude the need for any number of the other tests.

A)  Measure AC Voltage across each red lead to engine ground at cranking speed. (Leads disconnected from modules.)

·       5 – 7 VAC on each lead:   Specification measurement;  All OK.


NOTE::  during B & C tests, I will flex the harness at pinch points. Reading changes will represent failure.


B)  Check resistances across each red lead to engine ground:

·       3.2 – 4.5 OHMS on each lead:   Specification measurement;  All OK.

·       0 OHMS:   Short to ground  (failure)

·       INFINITY OHMS: broken lead wire  (failure)

C)  Check resistance across the disconnected  red wire leads from the charging coils:

·       3.2 – 4.5 OHMS:  one lead wire is shorted to ground (failure)

·       INFINITY OHMS:   broken lead wire with no grounding or shorting of leads. (failure)

·       0 OHMS:  shorting of leads or possible grounding of BOTH lead wires. (failure)

·       SMALL RESISTANCE:  (half of 3.2 – 4.5 ohms)  All OK.  (measures resistance from lead through the first coil to ground then back through the other coil and second lead.)

D)  Attempt to start the engine while an assistant sprays fuel into the intake end of the carburetor(s). Any detonation indicates the presence of spark. Explosion and fire indicates the need for insurance.

E)  Ignition on; module(s) connected.  Engage the starter with the top plugs removed, connected and  grounded while an assistant looks for spark at the gaps. Results will also depend upon which modules/sparkplug coils are connected.

F)  Look for rats & squirrels in the exhaust pipe.




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Sounds like a plan, Dan.


The only thing I would add (if you get no result from your proposed list) is to again measure the charging coil outputs to the ignition modules, with the ignition modules connected.


The reason is this:

When disconnected, the charging coils are under no load, they are not delivering any current (aside from the minute amount required by your meter).

When connected, the coils are under load and delivering current as they would in the usual 'live' situation.


The best parallel I can think of is of a failing 12V battery:

If you measure the voltage with nothing connected to the battery (no load) you are likely to see 12V and it all looks good.

However, if you put the battery under load, it can no longer deliver sufficient current, and the voltage drops accordingly.

For this reason, the battery test a lot of workshops use (or used to use, I haven't checked for a bit) is momentarily subjecting the battery to a dummy load (usually a big resistor), while measuring to see if the voltage drops.

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PS: If you're going to wiggle wires etc, do it in a very measured and progressive manner.

Right now you have a solid fault, which is bigly much  preferable to an intermittent fault.

So if wiggling stuff does make a difference, you need to be very clear which wiggle did it........

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