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G3X Touch RPM erratic when actual RPM is low

iamtheari

Well Known Member
I flew my plane a couple of times today and noticed something weird. When the engine is at a low idle (throttle all the way out, which should be around 600 RPM based on where I have the idle set at the engine) I get erratic RPM readings on my panel, ranging from 60 RPM up to 5,000 RPM. When I push the throttle in a bit to get to a more normal idle of 800-900 RPM, the reading is stable and correct.

My RPM is fed to the GEA 24 from the RPM output wire on my E-mag. This didn’t seem to happen until today and the plane has been flying for about 18 months and 130 hours. A loose wire is possible but I would expect erratic readings at higher RPMs, not only low idle.

Any ideas on places to check first without having to stand on my head to get to where I put the GEA 24 or, even worse, disassemble the connector for it?
 
I know little about the Pmag, but I suspect there is a VR or hall sensor to pick up an RPM. I have heard many mention that bearing failures are common on the Pmag. If the bearing goes bad, it can increase the gap between the sensor and metal tab or magnet on the spinning part, making it hard for the sensor to read the revolutions correctly. I would expect the problem to be the worst at the lowest RPM, as inertia/precession is not working as well to hold the spinning part stable

Symptoms don't really point to a wiring or instrument issue, as it wouldn't be limited to just low RPM, at least not over the long term. That said, I imagine vibrations are significantly higher at 600 RPM than anywhere else.

Larry
 
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First thing I’d do is give Brad at Emagair a call first thing Monday - he’s seen just about everything on his ignitions, and he’s probably got the answer for you.
 
I have a similar problem with my setup.
Lycoming YIO 360 M1B
Right hand P mag and dual G3X touches.
My issue is only at idle when the rpm becomes erratic. It has been suggested that it could be the grounding, when at an rpm giving the worst vibration. I didn't build the plane, I took the faster route and purchased it.
RV7 only got 55 hours from new build.
Any suggestions on where to start?
 
Erratic low rpm

At about 800 rpm the E-mag is self supportive.
The rpm signal on the E-mag needs to be configured as 5 or 12 V.
Check what the input terminals on the GEA24 requires 5 or 12V.

Good luck
 
Consider the possibility that the Emag that has the RPM lead connected to the G3X may have an intermittent power or ground lead. The EMag needs ship power below a certain RPM and you may be having a power issue on that EMag.
 
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