Erratic RPM

R

rtairey

New Member
Joined
May 15, 2011
Messages
59
In the last couple weeks, the RPM display jumps from normal values up a few hundred rpm and back down again just as quickly (engine running normally). It is now doing it every 10 seconds or so. It is very irritating as it sets the audible alarm off constantly. I have not yet updated to v14. Since there is no real sensor for the tach, could it be a failed in-line resistor? Appreciate an update if anyone else has seen, and corrected, this.
 
What engine? What ignition system? If dual ignition, does it do it on either ignition system?
 
I have the exact same issue running 2300rpm or above it jumps to 2800 or so and triggers alarming.
I thought maybe by coincidence that the resistors were loose or something, but it did get worse after v14.
Lycoming IO540
2 Mags
I have the EMS that was updated due to the spikes when pressing PTT
 
I have an IO320 with dual Bendix impulse mags. I did not think to try each mag seperately. I will do that next time up.
 
If you've had reliable rpm indications that are changing suddenly, the first thing to check is your ignition systems. Fouled plugs, improper gaps or worn points in the mag can lead to problems with the indicated rpm derived from p-lead resistors.

The IO-540 is 50% more susceptible to this issue.

Vern
 

I had this problem once.   It was caused by a loose connection on the inline resistor from the mag to the Skyview EMS sensor.

A loose contact will give a high rpm indication due to the engine vibrating the connection.  I moved the resistor further away from the mag and that solved my problem.
 
You must log in or register to reply here.
Back
Top