DETROIT DIESEL 53
TROUBLE SHOOTING 2.0
FUEL PUMP
MAINTENANCE
The fuel pump is so constructed as to be inherently trouble free. By using clean water-free fuel and
maintaining the fuel filters in good condition, the fuel pump will provide long satisfactory service and require
very little maintenance.
However, if the fuel pump fails to function satisfactorily, first check the fuel level in the fuel tank, then make
sure the fuel supply valve is open. Also check for external fuel leaks at the fuel line connections, filter gaskets
and air heater lines. Make certain that all fuel lines are connected in their proper order.
Next, check for a broken pump drive shaft or drive coupling. Insert the end of a-wire through one of the pump
flange drain holes, then crank the engine momentarily and note whether the wire vibrates. Vibration will be felt
if the pump shaft rotates.
All fuel pump failures result in no fuel or insufficient fuel being delivered to the fuel injectors and may be
indicated by uneven running of the engine, excessive vibration, stalling at idling speeds or a loss of power.
The most common reason for failure of a fuel pump to function properly is a sticking relief valve. The relief
valve, due to its close fit in the valve bore, may become stuck in a fully open or partially open position due to a
small amount of grit or foreign material lodged between the relief valve and its bore or seat. This permits the
fuel oil to circulate within the pump rather than being forced through the fuel system.
Therefore, if the fuel pump is not functioning properly, remove the relief valve plug, spring and pin and check
the movement of the valve within the valve bore. If the valve sticks, recondition it by using fine emery cloth to
remove any scuff marks. Otherwise, replace the valve. Clean the valve bore and the valve components.
Then lubricate the valve and check it for free movement throughout the entire length of its travel. Reassemble
the valve in the pump.
After the relief valve has been checked, start the engine and check the fuel flow at some point between the
restricted fitting in the fuel return manifold at the cylinder head and the fuel tank.
CHECKING FUEL FLOW
1. Disconnect the fuel return tube from the fitting at the fuel tank or source of supply and hold the open end of
the tube in a convenient receptacle.
2. Start and run the engine at 1200 rpm and measure the fuel flow return from the manifold. Refer to Section
13.2 for the specified quantity per minute.
3. Immerse the end of the fuel tube in the fuel in the container. Air bubbles rising to the surface of the 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. f 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 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.
If the engine still does not perform satisfactorily, one or more fuel injectors may be at fault and may be checked
as follows:
1. Run the engine at idle speed and cut out each injector in turn by holding the injector follower down with a
screw driver. If a cylinder has been misfiring, there will be no noticeable difference in the sound and operation
of the engine when that particular injector has been cut out. If the cylinder has been firing properly there will be
a noticeable difference in the sound and operation of the engine when the injector is cut out.
2. Stop the engine and remove the fuel pipe between the fuel return manifold and the injector.
3. Hold a finger over the injector fuel outlet and crank the engine with the starter. A gush of' fuel while turning
the engine indicates an ample fuel supply; otherwise, the injector filters are clogged and the injector must
be removed for service.
Page 12
