As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING COMPLETION OF ENGINE GROUND RUNS AFTER AN ENGINE CHANGE, THE ENGINE BOTTOM GOVERNING FUNCTION COULD NOT BE CONSISTENTLY ENABLED AS REQUIRED BY THE CHECK. IT WOULD INTERMITTENTLY FAULT TO A LOWER THAN SELECTED RPM. THE HMU WAS REPLACED AND SENT TO THE MANUFACTURER FOR INSPECTION AND REPAIR.