Mag test fails ... but ONLY at low RPM?

Thanks Bill!

 You wrote..

"Does it die suddenly and peacefully or is there a second or two of Death-Rattling before it succumbs?"

I've essentially done that test. As best I remember (but I'd want to try it again watching and listening carefully) it was more like(A) there was a grey zone around 2100 or 2200 RPM where it ran rattling rather than (B) sudden complete shut down.

I'm not SURE how you suggest _interpreting_ A vs B?

Which of those scenarios is the one that suggests the spacing/position of the trigger coil is out? Sounds like that would be "B". Right?

And if it isn't trigger coil spacing that would seem to go back to "one ignition model getting flaky?" ... Which should diagnosed by the swap Garret suggests. But, humm. If we swap the ignition modules (or cross wire them) are we ALSO swapping the trigger coil? So does Garrett's procedure really narrow it down to a flaky module if the problem moves to the other mag-test switch?

By the way:

Reading about the trigger coils (which merely trigger the ignition modules to fire, not, as in traditional magnetos, generate a current pulse for a spark) seems to confirm my suspicion that, unlike traditional magnetos, if one had an alternator failure on a cross country flight that once the battery ran down there'd be no ignition and engine would shutdown.

The rotax 912 ignition system produces it own power similar to a magneto. It does not require a battery and or charge system to function.

"The rotax 912 ignition system produces it own power similar to a magneto. It does not require a battery and or charge system to function."

Hummm! Good to hear. Curious HOW it does so? Any idea?

The 912 has a magneto, just not in the common external bolt on configuration.

Look at the Manual Schematic.

The stator has 10 coils.

8 Generator Coils power the panel.

2 Charging Coils Power the Ingitions. One each.

The trigger coils perform the timing.

The Charging Coil, Trigger Coil and Ignition Module comprise a "Magneto".

- - -

A bad module would kill all 4 plugs simultaneously resuting in a swift but peaceful stall.

It is most likely that ony ONE trigger coil is in troube, NOT Both!

If one is out you will lose 2 of the 4 plugs and end up with a 2 cylinder rough running engine that soon stalls out.

- - -

You have a 912-UL.

Swapping the 4 pin connectors swaps ONLY the Trigger and Charging Coil. (Not the Mag Switches.)

If the problem swaps sides, it is the coils ... If nothing changes, it is the modules.

Modules = Money$$$ . . .  Coils = Labor!!!