4. Fuel pump (supply pump, not an injection
5. Fuel strainer or primary filter.
6. Fuel filter (secondary).
7. Fuel lines.
8. One-way check valve.
9. Restricted fitting on in-line engines or a
restricted TEE on V-type engines.
The fuel pump is a positive displacement gear-type
unit that transfers fuel from the tank to the injectors at 65
to 75 psi (fig. 5-24). The standard pump has the ability
to deliver 1.5 gallons per minute, or 90 gallons per hour.
The fuel pump body and cover are aligned by means
of two dowels. The body and cover are machined
surfaces that contain no gasket between them, although
a thin coat of sealant applied to these surfaces is
recommended at installation. A relief valve bypasses
fuel back to the inlet side of the pump when pressure
reaches above the 65 to 75 psi.
There are two oil seals pressed into the pump bore
from the flanged end for the following purposes:
1. The seal closest to the drive coupling prevents
lube oil from entering the fuel pump.
2. The inner seal closest to the pump gears
prevents fuel leakage.
The installed seals do not butt up against each other,
but have a small space between them. Drilled and taped
Figure 5-24.Typical gear fuel pump assembly.
into this cavity in the fuel pump body are two small
holesone which is usually plugged and the other one
is open to allow any fuel or lube oil to drain, thereby
indicating damaged seals. Sometimes a small fitting
and tube extend from one of these holes to direct any
leakage to a noticeable spot. Acceptable leakage should
not exceed 1 drop per minute.
If you are ever in doubt as to the rotation of the fuel
pump, it can be identified as follows:
Stamped on the pump cover are the letters LH or
RH, plus an arrow indicating the direction of
On in-line engines, the rotation of the fuel pump
can be determined by its location on the engine.
When viewed from the flywheel end: left-hand
side location, LH pump rotation; right-hand side
location, RH pump rotation.
A similar method would be to grasp the pump in
your left or right hand, as it mounts on the
engine. Whichever thumb covers the relief
valves indicates the rotation of the pump.
The letter I/L (inlet) is also stamped on the pump
cover; however, if not visible, the inlet side is the hole
on the pump cover closest to the relief valve plug.
Since the pump constantly circulates a supply of
fuel to and through the injectors, the unused fuel cools
and lubricates the injectors and purges the system of any
air, then returns to the fuel tank via the restricted fitting
and return line.
All Detroit diesel engines are equipped with a
return Line restricted fitting, the actual size varying with
the engine injector size and application. Every
restricted fitting has the letter R followed by a number
that indicates its hole size in thousandths of an inch.
Therefore, a fitting with R80 stamped on it indicates a
0.080-inch-diameter hole drilled within the fitting.
These fittings may look like an ordinary brass
fittings externally; therefore, care must be taken to
ensure that, in fact, the proper restricted fitting, and not
just any fitting, is installed into the return line. Use of
too large a fitting can lead to a low fuel pressure within
the fuel manifold. This condition can cause poor engine
performance. A small fitting can lead to increased fuel
temperatures and some restriction against the fuel flow.
Refer to the service manual of the engine for any