GM 6.5L V8 – Fuel System – Fuel Injection Pump Assembly

Injection Pump Mounting and Drive

The fuel injection pump assembly mounts on the rear of the front cover, using a pilot bore, three stud/nut fasteners and a gasket. The injection pump mounting flange has a timing mark that aligns with a timing mark on the front cover during the installation procedure (see Figure 7-19, view A).
The injection pump drive gear is held on the front of the camshaft with a bolt and alignment dowel, and rotates a driven gear with a 1:1 ratio. The drive and driven gears have alignment marks for installation to assure correct timing (see Figure 7-19, view B).

The fuel injection pump driven gear mounts on the injection pump drive shaft flange, using a pilot bore, an alignment dowel and three bolts coated with thread-locking compound. The injection pump drive shaft has a center bore that allows a spring-loaded plunger to contact a metal finger on the back side of the water pump plate (see Figure 7-20, view A).
Because the gears use teeth cut in a helical pattern, end-play causes changes in fuel injection timing. The spring-loaded plunger provides thrust force on the injection pump drive shaft to control the end-play of internal parts. It also keeps the timing between the drive and driven gears from changing as the result of driven gear endwise movement.
During injection pump replacement, access to the three driven gear mounting bolts is possible after the oil fill pipe and grommet are removed (see Figure 7-20, view B). The crankshaft must be rotated for access to each of the bolts.

Injection Pump External Linkage

The fuel injection pump has an external bracket that supports the throttle cable assembly (see Figure 7-21, view A). The throttle cable attaches to the injection pump throttle shaft and connects with the accelerator pedal in the passenger compartment. Vehicles equipped with cruise control have a similar cable attachment to the injection pump.
The injection pump throttle shaft has a full-throttle stop screw that is pre-adjusted during calibration, as well as an idle speed screw that provides adjustment during service (see Figure 7-21, view B). A throttle return spring fastened between the bracket and injection pump keeps the throttle shaft in a closed position for engine idling.

Injection Pump Electrical Connections

The fuel injection pump has electrical connectors for four devices. The top of the injection pump (called the governor cover) contains an internal fuel shut-off solenoid with a B+ terminal that receives power when the ignition switch is in either the START or RUN position (see Figure 7-22). The shut-off solenoid ground is provided through the injection pump housing mounting to the engine.
Another electrical control inside the injection pump governor cover is the Housing Pressure Cold Advance (HPCA) solenoid. Like the shut-off solenoid, it has a B+ terminal and ground connection through the housing.
A third control, the fast idle solenoid, mounts on the external bracket, aligns with the throttle shaft and has a single B+ terminal. The fourth electrical device is the Throttle Position Sensor (TPS), an input to the Transmission Control Module (TCM).
Refer to Section 8 for more information about these electrical circuits.

Injection Pump Fuel System Connections

The fuel injection pump has a fitting on its transfer pump end cap for the hose from the fuel filter assembly. Fuel under lift pump pressure enters the injection pump at this location.
The governor cover of the injection pump has a fitting at its housing pressure regulator for a hose connecting to the fuel return system (see Figure 7-23, view A). The return system sends fuel heated by internal part movement inside the injection pump and injection nozzles to the fuel tank.
The injection pump head assembly has eight high-pressure outlet fittings for the lines connecting to nozzles in the cylinders (see Figure 7-23, view B). Each fitting connects with a specific cylinder.

Injection Pump Construction

The fuel injection pump pressurizes and distributes a metered amount of fuel to each cylinder nozzle at the proper time, based on the calibrated needs of the engine. The injection pump uses a variety of internal components that require lubrication from the very highly filtered fuel flowing around them (refer to Figure 7-24).
Some parts have surfaces with machining tolerances measured in microns (millionths of an inch) and require handling by skilled technicians operating in a “clean room” environment with a ventilation system using temperature, humidity and dust control. Other internal injection pump parts have adjustments that are made during a calibration procedure with a special test stand. For these reasons, very few repairs are made by dealership service technicians.

Injection Pump Operation

The operation of the fuel injection pump has four functions related to the delivery of fuel to the injection lines and nozzles:
• Metering
• Pressurization and distribution
• Lubricating
• Timing

The injection pump accomplishes its functions using fuel as a hydraulic fluid (refer to Figures 7-25 and 7-26).
Several different pressures exist in the injection pump as it operates. During service, test gauges may be installed to diagnose the fuel system.


Fuel under lift pump pressure enters the inlet of the transfer pump (refer to Figures 7-27 and 7-28). The drive shaft rotates the rotor, which has slots in its end to operate the blades of the transfer pump inside a stationary cam ring.
The transfer pump varies the pressure of the fuel, depending on the speed of the engine. At idle, the transfer pump outlet pressure is approximately 20 to 30 psi. At full engine speed, the transfer pump outlet pressure may be over 100 psi.
A regulator valve controls the transfer pump outlet pressure and has an adjustment made during injection pump calibration.

Fuel under transfer pump pressure travels through passages to several components, including a metering valve (refer to Figures 7-29 and 7-30). The metering valve directly affects the speed and power of the engine.
The metering valve controls how much fuel under transfer pump pressure enters a circular charging passage in the high-pressure part of the injection pump. When the valve rotates in a clockwise direction, less fuel enters the charging passage. As the valve rotates in a counterclockwise direction, more fuel enters the charging passage.

A governor mechanism positions the metering valve by balancing the opposing forces of the throttle shaft position and the speed of the injection pump. The governor mechanism includes the following parts (refer to Figure 7-31):
• The metering valve
• Linkage connected to the metering valve (not shown)
• The governor arm, connected to the linkage and pivoting on a pin in the injection pump housing
• Two parts that contact the governor arm:
– A governor weight assembly
– A min-max governor assembly

The governor weight assembly has these parts:
• A weight retainer, mounted on the rotor and rotated by the drive shaft
• Six weights that pivot further outward as injection pump speed increases
• A governor sleeve that is moved by the action of the weights and in turn moves the bottom end of the
governor arm

The min-max governor assembly has the parts shown in Figure 7-32, view A. It mounts in the injection pump housing by sliding on a guide stud and connects the throttle shaft to the upper end of the governor arm (see Figure 7-32, view B).

The governor mechanism operates as follows (refer to Figures 7-33 and 7-34):
• A fuel shut-off solenoid contacts the metering valve linkage when it is OFF, blocking fuel from entering the charging passage and stopping engine operation.
• At any engine speed, the metering valve is positioned by opposing forces:
– The throttle shaft position, acting on the governor arm/linkage with the min-max governor and the tension of its springs:
• Low idle
• Outer
• Inner
– The injection pump drive shaft speed, acting on the governor arm/linkage with force from the rotating weights and governor sleeve

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