As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) UPON GROUND RUNUP THE TACOMETER WAS OBSERVED TO HAVE A NEEDLE JUMPING/HUNTING BETWEEN 200 RPM, 100 UP AND 100 DOWN AT ANY RPM THIS WOULD HAPPEN. UPON USING A TACHOMETER CHECKER IT WAS OBSERVED THAT THE TACHOMETER WAS ACTUALLY READING 400 LOW ON THE RPM READ OUT. TACHOMETER WAS REPLACED AND TACHOMETER CABLE WAS ALSO REPLACED. UPON GROUND RUN UP REPLACED TACHOMETER AND CABLE FOUND TO BE OPERATING SERVICABLE.