Tachometer Fluctuations

[danburdette]

I have a D-180 with P-lead pickups on a Lycoming IO 320D1A with Slick mags.

This is the first day I have run the engine. RPM is indicating steady then will occasionally spike about 200-300 RPM upward and right back down to the previous steady RPM. Spike lasts about one-two seconds. Spikes occur about once per minute.

Any ideas?

Dan

 

[dynonsupport]

The EMS is designed to automatically search for RPM on the other mag if the one it's actively monitoring goes away. So if you have a mag that is intermittent, and is reading wrong/differently than the good one, then as it goes on and offline, it might be being alternately noticed and ignored by the EMS. So that's something to consider.

The other generic thing it could be is extra voltage pulses that are being counted by the EMS as revs. You can try upping the resistance, in increments (say 60k, then 100k, you can even go to 150k) to try to filter those pulses out. If you go too high, you may lose the actual signal, in which case RPM will erratic or low or simply gone.