As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DEPARTURE, THERE WAS A PARTIAL POWER LOSS. ACFT MADE AN UNSCHEDULED LANDING AT THE DEPARTURE AIRPORT. MAINTENANCE TECHS RAN ACFT ON THE GROUND WITH NO FAULT FOUND. INSPECTED THE ELECTRIC FUEL PUMP. INSPECTION REVEALED WASHER ENCIRCLING BALL VALVE WAS DISPLACED AND THE VALVE SEAT WAS SEVERELY WORN ALLOWING VALVE TO STICK CLOSED. SINCE THE FUEL SYSTEM IS ROUTED IN SERIES, THIS COULD CAUSE A RESTRICTION OF FUEL FLOW TO THE ENGINE AND SUBSEQUENT ENGINE POWER LOSS.