How to run an IO-320 at 10,000 rpm...

[DrillBit]

...before the first start, to boot.

A "has anyone seen/solved something like this before" question:

Two PMAGs, each tach signal monitored with Dynon Skyview EMS-220. Flip on the master, and the SC screen boots up indicating rpm in excess of 10,000 rpm.
Remove ship's power from the left PMAG, rpm falls to zero, so the problem is likely the left PMAG or wiring, grounding for same. Naturally, the left PMAG is mounted where the connector most inconvenient to access. Jiggling wires at the connector has no effect.

Problem has developed with the fuselage still at home. I'm going through and correcting my wiring documentation before riveting the last skin on. There was no redline (and then some) rpm on the initial smoke tests. Still no smoke--just a ton of noise into EMS DB37 pin 34 from somewhere...

Thoughts?

[Weasel]

Reduction drive should get your prop speed back down to something acceptable. Let it run at 10,000. Should make good power if you have a good fuel delivery system and it don't fly apart

[Jesse]

I would make absolutely sure you have the correct wires hooked up (verify pin, not just wire color). Then maybe check for shorts. Then check for correct settings, then switch connectors between mags and see if he problem follows the mag or follows the wiring harness.

[DrillBit]

Fortunately, observation and RTFMing prevented unneeded wrenching.

Observation: Left PMAG LED was a sickly, flickering orange color. Right PMAG was steady GREEN.

From the EMAGair's troubleshooting tips:

LED Signals: 5. After setting timing and resetting 12 volt power (your confirmation step when setting timing), the LED should be solid GREEN. However, if the engine happens to be positioned on the (very narrow) boundary between RED and GREEN, the LED will flicker rapidly between RED and GREEN (the combination sometimes looking amber or yellow). It?s not a problem. Your timing set was successful. Simply nudge the prop very slightly and you will see a solid RED or solid GREEN, depending on the direction.

Aha moment: Flywheels, spinner rear bulkhead has been on and off a zilliion times fitting cowl and baffling. I had felt the crank turn a degree or two this way and that.

Resolution: Moved the crank a degree or three. Both PMAG LED's were steady, one RED, the other GREEN as it happened. RPM fell to 0.000.... It seems the flickering LED sends a few 10 thousand pulses per minute down the tach sensor wire. Not much chance of that happening on a running engine.

No wrenching: PRICELESS!