As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE REPORTEDLY BACKFIRED AND SURGED AT HIGH POWER SETTINGS WHEN MAKING CHANGES IN POWER SETTING. ENGINE PASSED ALL GROUND PERFORMANCE CHECKS SO A FCU WAS REPLACED FOR TROUBLESHOOTING. ITS UNKNOWN WHAT CAUSED THE FCU TO MALFUNCTION DURING THE ACCELERATION MODE.