Ignition System Troubleshooting - 912UL

I'm not familiar with the Sportflight CDI modules and I cannot find any details online. I suspect that they are similar to the Ignitech modules that have built-in soft-start and an auxiliary 12V power supply to aid starting.

Given that you have changed so many components there is a lot to check through to see where the problem lies. You may have done some of the following but here are some thoughts:

Remove all the top spark plugs and position them so that you can see the electrodes of the top plugs and that the plug body is in contact with the engine body.

Refit your old CDi modules and crank the engine. Any spark?

Refit one of your old trigger coils and connect it to the CDI module. Crank the engine, look for a spark.

If you still don't have any luck, then visually inspect the new stator and rotate the engine by hand to ensure that the timing tabs pass the trigger coil poles correctly and the gap is as per the heavy maintenance manual.

Make sure the kill switch inputs are not grounded.

There are a number of resistance measurement specified in the manual which would be worth verifying.

All you need for a spark is: power to the CDI either through the stator coil or the aux 12V on the replacement CDI, a pulse of large enough amplitude on the coil trigger input, a correctly connected coil and a spark gap.

Hi all

First a few basics.  The CDI generates its own spark without input from a battery.  It however will require at least 225 to 250 crankshaft speed to maintain charge in the capacitor between trigger signals.  The standard 912 has a cross fire in that the A, top module, fires top 1 and 2 cylinder plug plus bottom 3 and 4 plug.  B fires the others.  

The trigger gap is sensitive and must be correct for the trigger type used (see heavy manual) Too large a gap and it will not fire.  Adjust as needed.  

Confirm with a good auto range meter that all ohm readings per the heavy manual are correct.  Confirm all grounds (the most common cause of problems)  

I have no data on the aftermarket parts so you must contact them however it is unlikely that both of the original ones failed at the same time.  

Also do not discount problems with the spark set or the connectors.  Be sure to check the high tension wires also.  (in the list of items to inspect from the heavy manual) 

Cheers

PS, when cranking to view a spark on a CDI the spark is very short and difficult to see in bright light.  Do this inside or in a shaded or dark area.  Confirm with an optical tack that you have 250 RPM at cranking (100 RPM on the prop) Take care ot be sure that the plugs are grounded so it will not backfeed and damage the capacitors inside. 

All 

From heavy manual, ohm checks.  

Cheers

I've done most of these steps, but will go back and verify my work. I have not carefully OHM checked each of the components and that will be my next step. I also have a set of known-to-be-working Ducati CDI's lent to me by a buddy which I'll reconnect and test next. 

Is there a signal check for the trigger coils? Restated, is there a way to verify the signal by cranking the engine and reading a voltage drop or surge? The OHM readings are all good, and I set the gap at .14 (.12 - .16 is what I remember seeing in the HMM).

In a separate post, during the rebuild I was concerned about the position of the trigger coils relative to the flywheel tabs.

Thanks again for the suggestions!

Hi again David

Given you are in the USA I might suggest you remove all the ignition and send it to an overhaul facility to have testing done on a live bench.  If you have done all the ohm tests and physical tests then i would certainly think that would be prudent.  I know Lockwood Aviation has a bench and coordinate with them on what they would like back.  That is the only "live" way to check any of the parts.

Cheers