My Left Engine Logged 18000 Hours on last flight! RPM issues

[TheFruck]

Hello,
New install in a Piper Seneca III. We have about 8 hours on the system since install. On my last flight, about 10 mins before landing, I started receiving Engine Speed warning messages and RPM indications on the LE were all over the place... Erratic... back and forth,,, I think I saw an indication over 5000 RPM. Of course it was quickly determined to be a indicator error as the engine was running just as smooth as the other.

I started some basic troubleshooting yesterday. I suspected that maybe the Plead pick off was loose on one of the mags (no such luck). I also notice that the recorded tach time on the Left side had added an extra 18000 hrs! I had not noticed that in flight.

My installation includes tach pick off from both pressurized magneto pleads through 30k resistors to the Standard RPM inputs at Pins 32/33

Plans for troubleshooting today include:
engine run up to see if I can reproduce the issue and isolate it to a specific magneto.
Measure resistance of inline plead resistors

Any other ideas?
Thank You

 

[skysailor]

Check every connection between the magneto and the EMS 220. It is almost certainly a bad connection "making and breaking". Verify the ground connection as well.

 

[TheFruck]

Just following up on this to share what was found. I had a failed mag. Simple mag check proved this. I am guessing that the erratic fluctuations and the absurd tach time was due to the EMS utilizing that mag lor pulses at the time of failure. Mag replaced, times adjusted... all better

 

[Rhino]

Thanks for coming back and letting us know.