Erratic tach readings

[Walt]

While flying yesterday, my tach readout on my Dynon Skyview started going crazy…. rpm were jumping all over the place between 2600 to 4000rpm!
It did this for about 10 minutes and then returned to normal for the last 10 min of the flight. The Dynon EMS is connected to the right mag only,( Have SureFly on left side). I checked the leads connections on the mag and they were tight…..
Any thoughts/ advice is appreciated!

Walt

Engine is a AeroSports Power O-375 . SureFly EIS / Slick mag
Dynon Skyview Classic EFIS
Total hours : 600

 

[Carl_Froehlich]

Try a higher value resistor in the mag tach lead, perhaps 40K-50K. See page 7-47 of the install manual.

Why do you not have the SureFly connected to the EMS tach input as well as the mag?

Carl

 

[Walt]

Try a higher value resistor in the mag tach lead, perhaps 40K-50K. See page 7-47 of the install manual.

Why do you not have the SureFly connected to the EMS

Try a higher value resistor in the mag tach lead, perhaps 40K-50K. See page 7-47 of the install manual.

Why do you not have the SureFly connected to the EMS tach input as well as the mag?

Carl

Thanks for the response….I’ve been flying the airplane for over 2.5 years, ( 230hours) and this is the first time this has happened.
I am not the builder so I’m not sure what resistor is installed, but why do you think it would all of a sudden need a higher value resistor? ( been working fine for 600 hours!)
After installing the SureFly, I discovered that the Dynon Skyview cannot read the tach output signal from the SureFly. Apparently there is a circuit board that must be installed to fix this….. I just have not gotten around to installing it.

 

[Carl_Froehlich]

Thanks for the response….I’ve been flying the airplane for over 2.5 years, ( 230hours) and this is the first time this has happened.
I am not the builder so I’m not sure what resistor is installed, but why do you think it would all of a sudden need a higher value resistor? ( been working fine for 600 hours!)
After installing the SureFly, I discovered that the Dynon Skyview cannot read the tach output signal from the SureFly. Apparently there is a circuit board that must be installed to fix this….. I just have not gotten around to installing it.

A magneto can put out a lot of noise, and this can show up on the p-lead. This noise can be mistaken by the EMS as a valid tach signal. The resistor helps to lower the overall signal, including the noise. The right value resistor will leave enough signal to trigger a real tach pulse but drive the noise (false signals) below what the EMS can pick up.

Don’t assume your magneto does not change over time, or for that matter moving wires around can influence the p-lead signal. Check your plugs and leads? Any recent maintenance ? Any change in the ignition noise in your headset of late?

I’m surprised SureFly cannot feed a tach signal to the EMS right out of the box. I only use pMags (four and six cylinder versions) so not familiar with SureFly.

Carl

 

[preid]

Is this the only time it has happened? has it happened before and not as bad?
if first time, wait until it does it a few times, Ive had this happen randomly if its happened before, Ive had that as well over time.
Ive replaced the resistor between the plead and mag a couple of times as it works fine for about 100 so hours than starts doing it again. It is especially apparent on my second flight when everything is really hot getting up to altitude. than it wont do it for a few flights.
If this happens randomly, check the wiring the resisitor is connected to, sometimes that connection gets loose and causes issues.
Suggestions
1) leave it alone unless it does it more often. if is does
a) check connection of resisitor for good connection,
b) OR while youre looking take a picture of resistor, and replace with new resistor