3-145. FUEL PUMP - MAINTENANCE INSTRUCTIONS.
a. The fuel pump is constructed to be basically trouble-free. Clean, water-free fuel, and maintenance of the
fuel filters, will give long, satisfactory service.
b. If the fuel pump fails to function satisfactorily:
check the level in the fuel tank.
Make sure the fuel supply valve is open.
Check for external fuel leaks at the fuel line connections, filter gaskets, and air heater lines.
Check for a broken drive shaft or drive coupling. Insert the end of a wire thru one of the pump
flange drain holes and crank the engine momentarily. Note if the wire vibrates. Vibration will be felt
if the pump shaft rotates.
c. All fuel pump failures result in no fuel or insufficient fuel being delivered to the fuel injectors and may be
Uneven running of the engine
Stalling at idling speeds
Loss of power
d. The most common reason for a fuel pump to function improperly is a sticking relief valve. The relief
valve, due to its close fit in the valve bore, may stick in a fully open, or partially open position. A small amount
of grit or foreign material, lodged between the relief valve and its bore or seat will cause the fuel oil to circulate
within the pump, rather than being forced thru the fuel system.
e. After the relief valve has been checked and the fuel pump reinstalled on the engine, start the engine.
Check the fuel flow between the restricted fitting in the fuel return manifold at the cylinder head, and the fuel