RPM changes at high power settings

[Battson]

Hey - new intermittent issue developed today.

When I was cruising at high power settings, the RPM started flicking from say 2300 to some fictitious higher value like 2560 for a second or a few seconds, and then back to the right value for just a moment, and so on.

Engine is an IO-540 with dual Bendix S6 mags, with L and R P-lead pick-ups at the ignition switich with the 30kOhm resistors wired in-line with each RPM pick-up, right at the P-lead.

I have had no issues with this so far. It only seemed to happen at high power settings. In particular, running over-square, but I doubt if that is related.

It has just come off a 100hr inspection, so the P-lead to magneto connections have been removed / reinstated once, some wires have been handled, and the plugs have been cleaned properly / tested etc.

Any suggestions?

Oh - EMS is D120, all Dynon harnesses/parts.

 

[jakej]

This problem can happen once in a while, I'd try increasing the resistor value in 10 or 20K increments but don't go higher than 120K - there is a device coming onto the market that eliminates this issue however more testing is needed, I'll report my results with this device later 

Jake J

 

[dynonsupport]

Fluctuating RPM indicates that the amplitude of the RPM signal into your EMS-D120 is too high for the EMS-D120 to accurately count the pulses. We second Jake J's suggestion to replace / increase the resistors inline from the P-Leads by 10,000-20,000 (10-20K) Ohms.

Hey - new intermittent issue developed today.

When I was cruising at high power settings, the RPM started flicking from say 2300 to some fictitious higher value like 2560 for a second or a few seconds, and then back to the right value for just a moment, and so on.

Engine is an IO-540 with dual Bendix S6 mags, with L and R P-lead pick-ups at the ignition switich with the 30kOhm resistors wired in-line with each RPM pick-up, right at the P-lead. 

I have had no issues with this so far. It only seemed to happen at high power settings. In particular, running over-square, but I doubt if that is related.

It has just come off a 100hr inspection, so the P-lead to magneto connections have been removed / reinstated once, some wires have been handled, and the plugs have been cleaned properly / tested etc.

Any suggestions?

Oh - EMS is D120, all Dynon harnesses/parts.

 

[Battson]

What can cause an increase in peak voltage in the P-leads over time?  This problem is new.