Tach fluctuation

[Donald_Eccker]

After 750 hrs and a HDX up grade two yrs ago my Tach has started jumping all over. Some times a little sometimes allot.
RV10 slick mags (300hrs on Mags).
not sure if it’s a Dynon thing or Mag thing so I thought I’d check here first.

 

[Stevec]

I would suspect either the wiring or the sensor. In particular check the earth connection to the engine block is not corroded or loose. The other main failure point would be any connectors in the wire from the sensor to the EMS. You do not say what sort of sensor is used in your system but I suspect you may have it on one of the magnetos.

 

[RVDan]

I just experienced the same thing with HDX. Very erratic and large rpm variations. I have a Mag on the left and EI on the right. The mag is input to the EMS via the 30k resistor called for in the manual. The EMS is connected directly. All have worked flawlessly for several years.
First thing was to check wiring. At the connection for the Mag all wiring checked out while wiggling wires. Checked the P lead at the mag. Same goes for the EI wiring. Can’t duplicate on the ground.