MAP showing RED X on power reduction

[Seagull]

Today when flying the MAP gauge went to a RED X for 5 seconds when reducing power in cruise to idle. This is the same RED X, you see with no input. Has anyone seen this or have suggestions to where to start looking for the problem?

My specifics. The panel is a Dynon Skyview, the engine is a Rotax 912ULS. I have flown this for 800 hours in the past 3.5 years and never seen this happen.

The RED X appears when I reduce power from cruise to Idle in flight. The RED X appears for about 5 seconds then the gauge reads numbers again. It will not go to the RED X again until I cycle the power from high to low again. I am posting this here and on the Rotax forum hoping someone has an idea.

 

[Dynon]

The MAP on your system is coming from a discrete sensor (not an ECU like on the iS motors). Red X will happen when the sensor either goes away (isn't working), or if it's dramatically exceed the valid output. So some possibilities: it could be wiring, that's tickled at some certain vibration during power change. Or possibly the sensor is on its way. If you save off your user data log, you could investigate what it's seeing just before it goes offline. You might set the recording rate to the fastest possible and try to capture it in the highest resolution detail if it isn't already cranked up.

 

[Seagull]

The MAP on your system is coming from a discrete sensor (not an ECU like on the iS motors). Red X will happen when the sensor either goes away (isn't working), or if it's dramatically exceed the valid output. So some possibilities: it could be wiring, that's tickled at some certain vibration during power change. Or possibly the sensor is on its way. If you save off your user data log, you could investigate what it's seeing just before it goes offline. You might set the recording rate to the fastest possible and try to capture it in the highest resolution detail if it isn't already cranked up.

I gave some thought to what you said and did some tests. At high altitude I pulled the throttle to idle from 25”, the “X” appeared for a few seconds then the pressure read again with engine at idle. I tried again starting at 20” and 15” each time got a “X”. Starting at 10” the “X” does not appear. Thinking vibration was the cause and still in flight I made small throttle changes from idle and up but could not make the “X” appear. Then my assumption was the sudden drop in pressure caused the sensor to foul. Once on the ground with the engine off I put a syringe on the hose to the sensor and pulled 25” and quickly released it the numbers fell as they should but I never saw the “x”. So it doesn’t seem to be vibration and doesn’t seem to be sudden pressure changes at least testing it the way I did.

 

[airguy]

I have seen the same behavior occasionally, if I pull the throttle all the way closed and the prop is driving the engine, resulting in MAP values around 4" or less, sometimes I'll get the Red X for a second or two. I have only seen this during a very low MAP scenario due to pulling the throttle completely closed at speed.