Diesel MFI Pump: Description and Operation

The V6-262 diesel engine may be equipped with one of two fuel injection pumps: the Roosa Master which can be identified by a looped fuel inlet pipe, and CAV pump which can be identified by a straight fuel inlet pipe.

Injection timing is controlled by two pressure regulators. One regulator is the Housing Pressure Cold Advance (HPCA), located in the pump. The other pressure regulator, used on 1984 except California models and all 1985 models, is the Housing Pressure Altitude Advance (HPAA), located in the fuel return line. The HPCA is designed to advance injection timing about 4° during cold operation. The HPAA will regulate housing pressure according to altitude.

Fig. 43 Roosa Master pump solenoids and connectors location:

Fig. 44 CAV pump solenoids and connectors location:

The Metering Valve Sensor (MVS), used on 1984 California models and all 1985 models with Diesel Electronic Control System, is a variable resistor which electronically signals the diesel ECM as to the position of the metering valve.

The injection pump is mounted on top of the engine. It is gear driven off the camshaft and turns at camshaft speed. It is a high pressure rotary pump that injects a metered amount of fuel to each cylinder at the proper time. The six high pressure delivery pipes from the pump to the injection nozzle in each cylinder are the same length to prevent any difference in timing, cylinder-to-cylinder. The fuel injection pump provides the required timing advance under all operating conditions. Engine RPM is controlled by a rotary fuel metering valve. Pushing down on the accelerator pedal moves the throttle cable to open the metering valve and allow more fuel to be delivered. The injection pump also has a low pressure transfer pump to deliver fuel from the fuel line to the high pressure pump.

The fuel filter is located between the electric fuel pump and the injection pump.

The fuel tank is at the rear of the vehicle, connected by fuel pipes and hoses to the fuel pump. Excess fuel returns from the fuel injection pump to the fuel tank through pipes and hoses.

Fig. 38 Roosa-Master pump fuel flow schematic. 1982-83 shown, 1984-85 similar:

Fig. 39 CAV pump fuel flow schematic:

The fuel flow schematics, Figs. 38 and 39, show the major components and their relationships and also provides a means of determining the differences in the two systems.