TM 53810-300-24&P-3
2.0
TROUBLE SHOOTING
FUEL PUMP
The fuel pump is so constructed as to be inherently
The most common reason for failure of a fuel pump to
trouble free.
By using clean, water-free fuel and
function properly is a sticking relief valve. The relief
maintaining the fuel filters in good condition, the fuel
valve, due to its close fit in the valve bore, may become
pump will provide long satisfactory service and
stuck in a fully open or partially open position due to a
require very little maintenance.
small amount of grit or foreign material lodged between
the valve and its bore or seat. This permits the fuel to
However, if the fuel pump fails to function satisfactorily,
circulate within the pump rather than being forced
first check the fuel level in the fuel tank, then make sure
through the fuel system.
the fuel supply valve is open. Also check for external
fuel leaks at the fuel line connections and filter gaskets.
Therefore, if the fuel pump is not functioning properly,
Make certain that all fuel lines are connected in their
remove the relief valve plug, spring and pin and check
proper order.
the movement of the valve within the valve bore. If the
valve sticks, recondition it by using fine emery cloth to
Next, check for a broken pump drive shaft or drive
remove any scuff marks. Otherwise, replace the valve.
coupling. Insert the end of a wire through the pump
Clean the valve bore and the valve components. Then
flange drain hole, then crank the engine momentarily and
lubricate the valve and check it for free movement
note whether the wire vibrates. Vibration will be felt if the
throughout the entire length of its travel. Reinstall the
pump shaft rotates.
valve.
All fuel pump failures result in no fuel or insufficient fuel
After the relief valve has been checked, start the engine
being delivered to the fuel injectors and may be indicated
and check the fuel flow at some point between the
by uneven running of the engine, excessive vibration,
restricted fitting in the fuel return manifold at the cylinder
stalling at idling speeds or a loss of power.
head and the fuel tank.
CHECKING FUEL FLOW
the fuel flow. Refer to Section 13.2 for the specified
1.
Disconnect the fuel return hose from the fitting at
quantity per minute.
the fuel tank and hold the open end in a convenient
3. Immerse the end of the fuel hose in the fuel in the
receptacle (Fig. 7).
container. Air bubbles rising to the surface of the
2.
Start and run the engine at 1200 rpm and measure
fuel will indicate air being drawn into the fuel system
on the suction side of the pump. If air is present,
tighten all fuel line connections between the fuel
tank and the fuel pump.
4. If the fuel flow is insufficient for satisfactory engine
performance, then:
a. Replace the element in the fuel strainer. Then
start the engine and run it at 1200 rpm to check
the fuel flow. If the flow is still unsatisfactory,
perform Step "b" below:
b. Replace the element in the fuel filter. If the flow
is still unsatisfactory, do as instructed in Step
"c".
c. Substitute another fuel pump that is known to
be in good condition and again check the fuel
Fig. 7 - Measuring Fuel Flow
flow. When changing a fuel pump, clean all of
the fuel lines with compressed air and be sure
all fuel line connections are tight. Check the
fuel lines for restrictions due to bends or other
damage.
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