What was found
PILOT REPORTED ERRATIC FUEL PRESSURE INDICATION DURING FLIGHT. AIRCRAFT ARRIVED AT MAINTENANCE BASE WHERE INSPECTION OF THE FUEL PUMP REVEALED FUEL SEEPING FROM PRESSURE RELIEF DIAPHRAGM VENT. UPON REMOVAL OF THE DIAPHRAGM, IT WAS NOTED THAT THE DIAPHRAGM RETAINING NUT WAS LOOSE DUE TO IMPROPER ENGAGEMENT OF THE LOCKING CLIP. DUE TO THE LOOSENESS OF THE RETAINING NUT, FUEL WAS ALLOWED TO LEAK PAST THE DIAPHRAGM CRUSH GASKET, FLOODING THE AMBIENT SIDE OF THE DIAPHRAGM. THIS ACTION PREVENTED THE RELIEF MECHANISM TO PROPERLY REGULATE THE FUEL PRESSURE. IT IS IMPORTANT TO REMOVE ANY FUEL PUMP OF THIS TYPE FROM SERVICE IF THERE IS ANY SIGN OF LEAKAGE FROM THE VENT AREA.