Dynon 180 issue

Lost in flight my rpm reading!
Start for a few minutes to read many numbers between 2000 and 2400 and goes to 0
Somebody had already this problem?
Installed on Lycoming 180 with normal magnetos
Thanks

Sounds like a bad ground or loose connection to the mag. Get the wiring diagram from the D180 installation and check both.

Check the back of the mag switch. This is the usual place the D180 tachometer wires connect. There will be a resistor in-line. The resistor breaks electrically from vibration because it is a single solid strand. Mounting it at this end requires care to isolate it from vibration but is superior from an electrical noise point of view.

Soni need to check behind the ignition key and at the magnetos ?

If it’s a loose P-lead at the mag it will cause this too I guess. But that is a more serious problem and more easily detectable at mag check. I’d check behind the key switch first.