Diagram of the operation of a fuel injection pump
(1) Drive shaft
(6) Plunger spring
(3) Control sleeve
(8) Deliver Valve
The fuel injection pump transfers fuel to the fuel injection
nozzles at high pressure. A cam (5) is driven from the engine
by a gear (2). Lobes on the cam (5) cause the plunger to
reciprocate. The reciprocating motion first draws the fuel. The
reciprocating motion then pressurizes the fuel.
The plunger (7) also rotates with the cam (5) in order to
sequentially align the discharge groove of the cam with each of
the ports on the fuel injector pump. The plunger (7) moves a
distance which is established by the lobes of the cam.
The effective stroke is established by the position of the control
sleeve. When the control sleeve is moved to the left prior to
injection of the fuel, the spill port is uncovered. Uncovering the
spill port reduces the amount of fuel that is delivered to the
cylinder. When the control sleeve is moved to the right prior to
injection of the fuel, the spill port is covered. Covering the spill
port increases the amount of fuel that is delivered to the
The pump also includes an internal timer (not shown). The
timer allows early fuel injection by advancing the plunger. The
plunger is advanced in relation to the camshaft. The solenoid
(4) is normally closed. When the voltage is applied, the
plunger moves in order to block the fuel delivery which stops
The fuel injection pump pumps the fuel from the fuel tank
through filters. The fuel flows through the center of the rotor of
the injection pump into a circular groove on the rotor. The fuel
then flows to the automatic advance and through a connecting
passage to the metering valve. The radial position of the
metering valve is controlled by the governor.
The metering valve regulates the flow of the fuel to the
discharge ports. When the rotor revolves, the two inlet
passages of the rotor match up to the discharge ports which
are located in the hydraulic head. The discharge ports allow
the fuel to flow into the pumping chamber. When the rotor
rotates further, the discharge port of the rotor matches up with
one of the outlets of the hydraulic head. When the discharge
port is opened, the rollers contact the lobes of the cam which
forces the plungers together. Fuel that is trapped between the
plungers is then pressurized. Then, the fuel flows to the fuel
injection nozzle. The fuel injection nozzle delivers the fuel to
When fuel reaches the discharge ports, slots on the rotor allow
the fuel and any air which is entrapped to flow into the cavity of
the pump housing. A passage in the hydraulic head connects
the outlet side of the transfer pump with the pump housing.
This passage vents the air from the fuel injection pump through
the fuel return line. This passage also allows some fuel to leak
back to the fuel tank through the fuel return line.
The fuel which leaks back to the fuel tank performs the
following function before being discharged through the fuel
The housing is filled with fuel, which helps prevent
any buildup of air.
The internal components are lubricated.
The fuel injection pump is cooled.
Small air bubbles are removed.
When the fuel injection pump is operating normally, the
housing must be completely full of fuel. The fuel injection
pump is self-lubricating.
Fuel Injection Pump For Type I Engines and 9RM
For a complete description of Type 1 and Type 2
engines, refer to the Systems Operation, Testing
and Adjusting Module, "Engine Design for more