DETROIT DIESEL 53
2.0 Trouble Shooting
FUEL PUMP MAINTENANCE
The most common reason for failure of a fuel pump
The fuel pump is so constructed as to be inherently
to function properly is a sticking relief valve. The
trouble free. By using clean water-free fuel and
relief valve, due to its close fit in the valve bore. may
maintaining the fuel filters in good condition, the fuel
become stuck in a fully open or partially open position
pump will provide long satisfactory service and
due to a small amount of grit or foreign material
require very little maintenance.
lodged between the relief valve and its bore or seat.
H o w e v e r , if the fuel pump fails to function
This permits the fuel oil to circulate within the pump
satisfactorily, first check the fuel level in the fuel tank,
rather than being forced through the fuel system.
then make sure the fuel supply valve is open. Also
check for external fuel leaks at the fuel line
Therefore, if the fuel pump is not functioning
connections, filter gaskets and air heater lines. Make
properly. remove the relief valve plug. spring and pin
certain that all fuel lines are connected in their proper
and check the movement of the valve within the valve
order.
bore. If the valve sticks, recondition it by using fine
emery cloth to remove any scuff marks. Otherwise,
Next, check for a broken pump drive shaft or drive
replace the valve. Clean the valve bore and the valve
coupling. Insert the end of a wire through one of the
components. Then lubricate the valve and check it for
pump flange drain holes, then crank the engine
free movement throughout the entire length of its
momentarily and note whether the wire vibrates.
travel. Reassemble the valve in the pump.
Vibration will be felt if the pump shaft rotates.
After the relief valve has been checked, start the
All fuel pump failures result in no fuel or insufficient
engine and check the fuel flow at some point between
fuel being delivered to the fuel injectors and may be
the restricted fitting in the fuel return manifold at the
indicated by uneven running of the engine, excessive
cylinder head and the fuel tank.
vibration, stalling at idling speeds or a loss of power.
CHECKING FUEL FLOW
When changing a fuel pump. clean all of the fuel
1. Disconnect the fuel return tube from the fitting at
lines with compressed air and be sure all fuel line
the fuel tank or source of supply and hold the open
connections are tight. Check the fuel lines for
end of the tube in a convenient receptacle.
restrictions due to bends or other damage.
2. Start and run the engine at 1200 rpm and measure
the fuel flow return from the manifold. Refer to
If the engine still does not perform satisfactorily, one
Section 13.2 for the specified quantity per minute.
or more fuel injectors may be at fault and may be
checked as follows:
3. Immerse the end of the fuel tube in the fuel in the
container Air bubbles rising to the surface of the fuel
1. Run the engine at idle speed and cut out each
wiII indicate air being drawn into the fuel system on
injector in turn by holding the injector follower down
the suction side of the pump. If air is present, tighten
with a screw driver. If a cylinder has been misfiring,
aII fuel line connections between the fuel tank and the
there will be no noticeable difference in the sound and
fuel pump.
operation of the engine when that particular injector
has been cut out. If the cylinder has been firing
4. If the fuel flow is insufficient for satisfactory engine
properly there will be a noticeable difference in the
performance. then:
sound and operation of the engine when the injector is
a. Replace the element in the fuel strainer. Then
cut out.
start the engine and run it at 1200 rpm to check
2. Stop the engine and remove the fuel pipe between
the fuel flow. If the flow is still unsatisfactory.
the fuel return manifold and the injector.
perform Step "b" below.
3. Hold a finger over the injector fuel outlet and crank
b. Replace the element in the fuel filter. If the flow is
the engine with the starter. A gush of fuel while
still unsatisfactory, do as instructed in Step "c".
turning the engine indicates an ample fuel supply:
c. Substitute another fuel pump that is known to be
otherwise, the injector filters are clogged and the
injector must he removed for service.
in good condition and again check the fuel flow.
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