the fuel supply valve is open. Also
NOTE
check for external fuel leaks at the fuel
line connections and filter gaskets.
With the engine at rest, all injec-
Make certain that all fuel lines are con-
tors will leak to some extent when
nected in their proper order.
pressurized. The leakage occurs
because there is no place else for
Next, check for a broken pump drive
the pressurize fuel to go. When
shaft or drive coupling. Insert the end
the low and high pressure cavities
of a wire through the pump flange drain
in the injector are subjected to the
hole, then crank the engine momentarily
high test pressure, fuel is forced
and note whether the wire vibrates. Vi-
past the plunger into the rack and
bration will be felt it the pump shaft
gear cavity. Result: Droplets of
rotates.
fuel form at the rack and drip off.
All fuel pump failures result in no fuel or
Slightly worn plungers may leak
insufficient fuel being delivered to the
more under these conditions. This
fuel injectors and may be indicated by
leakage will not occur while the
uneven running of the engine, excessive
engine is running because of the
vibration, stalling at idling speeds or a
dynamic and pressure conditions
l o s s of power.
that exists.
The most common reason for failure of a
If injectors are suspected of leak-
fuel pump to function properly is a stick-
ing and contributing to dilution of
ing relief valve. The relief valve, due
the lube oil, they should not be
to its close fit in the valve bore, may be-
tested by pressurizing the fuel
come stuck in a fully open or partially
system as described in 2 above.
open position due to a small amount of
Injectors should be removed from
grit or foreign material lodged between
the engine and tested for pressure
the valve and its bore or seat. This
holding capability.
permits the fuel to circulate with the
pump rather than being forced through
the fuel system.
Lube oil puddle inspection is the key to
pressure testing the fuel system for in-
Therefore, if the fuel pump is not func-
ternal leaks. This test can be performed
tioning properly, remove the relief valve
any time the rocker covers are removed,
plug, spring and pin and check the
after the fuel pipes and connectors have
movement of the valve within the valve
been splashed with oil and there is nor-
bore. If the valve sticks, recondition it
mal fuel pressure in the system. The
by using fine emery cloth to remove any
weak or missing puddles show where the
scuff marks. Otherwise, replace the
leaks are.
valve. Clean the valve bore and the
valve components. Then lubricate the
All leakage or spillage of fuel during leak
valve and check it for free movement
detection testing further dilutes the lube
thoroughout the entire length of its
oil, so the final step in maintenance of
travel. Reinstall the valve.
this type should include lube oil and lube
oil filter changes.
After the relief valve has been checked,
start the engine and check the fuel flow
at some point between the restricted fit-
TROUBLESHOOTING
ting in the fuel return manifold at the
cylinder head and the fuel tank.
F u e l Pump
C h e c k i n g Fuel Flow
The fuel pump is so constructed as to be
inherently trouble free. By using clean,
1. Disconnect the fuel return hose from
water-free fuel and maintaining the fuel
the fitting at the fuel tank and hold the
filters in good condition, the fuel pump
open end in a convenient receptacle.
will provide long satisfactory service and
(see Figure 11C-79 on page 11C-51).
require very little maintenance.
2. Start and run the engine at 1200 RPM
However, if the fuel pump fails to func-
and measure the fuel flow.
Refer to the
tion satisfactorily, first check the fuel
level in the fuel tank, then make sure
