The RPM rise during ign. check on an RV-12iS is normal.
My understanding was that it was because of #2 below.
I have never heard of #1 (but that doesn't mean it is not true).
Originally Posted by jcl777
Found these two interesting tidbits from two different threads in the forums at rotax-owner.com. Interesting.
The Fuel injected 912iS and 915iS engines use an ECM module that does NOT fire both plugs at the same time.
The Plugs fire alternately on every other cycle.
This allows the ECM to identify which plug in which cylinder might have a problem and remove it from the firing sequence with no power loss and the only indication being a warning light on the panel.
When performing an ignition check on these engines, the ECM fires the same plug on every cycle resulting in no rpm loss.
And because the ECM also enrichens the mixture slightly because it thinks there is an ignition failure, The engine RPM actually INCREASES during the ignition check.
Sometimes during lane checks the RPM will actually rise then once both lanes are back on it will decrease back where it was. The mixture is just going full rich and thus more power.
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Van's Aircraft Engineering Prototype Shop Manager
RV-6A (aka "Junkyard Special ")