Underreading tacho indication

[MJCATT]

Ran Superior XP-IO360 today for first time. RV-9A fitted with EMS-D120 and EFIS-D100. Everything normal except underreading tacho (by several hundred rpm). Will check with hand held tacho tomorrow but pretty sure there is a problem with the EMS somewhere.
Has anyone else had a similar problem?

 

[dynonsupport]

Keep in mind that the pulses per revolution is configurable under the EMS SETUP>SENSORS>TACH menu.