Diesel MFI Pump: Description and Operation

Fuel Flow:

The fuel injection pump accurately meters and delivers fuel to a nozzle in each cylinder at high pressure and at precisely timed intervals.
The injection pump is an opposed plunger, inlet metered, positive displacement, distributor type pump. The pump incorporates a single pumping chamber, an integral fuel transfer pump and governor, and an automatic injection advance mechanism. On-off control is provided by means of an electric solenoid located in the housing cover.
Fuel flows into the injection pump inlet through an inlet filter screen (1). Fuel then flows to the vane-type fuel transfer pump (2). Excess fuel from the transfer pump is bypassed through the pressure regulator assembly to the suction side.

Injection Pump Internal View:

Fuel under the transfer pump pressure flows through the center of the transfer pump rotor, past the rotor retainer (4) into the hydraulic head. It will then flow through a connecting passage (5) in the head to the automatic advance (6) and up through a radial passage to the metering valve (8). The position of the metering valve, controlled by the governor, regulates fuel flow into the radial charging passage (9) which incorporates the head charging parts. As the rotor revolves, the two rotor inlet passages (10) align with the charging ports in the hydraulic head, allowing fuel to flow into the pumping chamber. With addition rotation, the inlet passages move out of alignment and the discharge port of the rotor aligns with one of the head outlets. While the discharge port is opened, the rollers (11) contact the cam lobes forcing the plungers together. Fuel trapped between the plungers is then pressurized and delivered by the nozzle to the combustion chamber.
The air vent passage in the hydraulic head connects the outlet side of the transfer pump with the pump housing. This allows air and some fuel to be bled back to the fuel tank through the return lines. Fuel bypassed in this way fills the housing, lubricates the internal components, cools and carries off any small air bubbles.