Fuel System Description. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 Fuel System Description

The fuel injection system has a PCM controlled fuel injection pump which is mounted on top of the engine under the intake manifold. The pump is driven by the camshaft through two gears, one attached to the front of the camshaft and the other attached to the end of the pump shaft. These gears are the same size and have the same number of teeth; therefore, the injection pump shaft turns at the same speed as the camshaft.

Electronic Fuel Injection Pump


(1)	Fuel Solenoid Driver
(2)	Optical/Fuel Temperature Sensor
(3)	Fuel Inlet
(4)	Engine Shutoff Solenoid
(5)	Two Stage Housing Pressure Regulator
(6)	Injector Timing Stepper Motor
(7)	Fuel Solenoid

The injection pump is a high pressure rotary type that is controlled by the PCM. The injection pump meters, pressurizes, and distributes fuel to the eight injector nozzles by way of eight high pressure lines. An outlet port in the injection pump allows the fuel to enter the fuel return system and then travel back to the fuel tank.

Each cylinder has an identical fuel injection nozzle mounted in the pre-combustion chamber. As the pressure wave of injection reaches a nozzle, the needle valve is lifted against spring force, allowing the fuel to exit into the pre-combustion chamber of the cylinder as a highly atomized spray. A small amount of fuel travels between the needle valve and pintle nozzle, providing a lubrication. The two passages inside of the upper half of the nozzle body allows fuel which has lubricated the needle valve in order to exit into the fuel return system.


(1)	Cylinder 8
(2)	Cylinder 7
(3)	Cylinder 2
(4)	Cylinder 6
(5)	Cylinder 5
(6)	Cylinder 4
(7)	Cylinder 3
(8)	Cylinder 1

The injection lines connect the high pressure discharge fittings on the head of the injection pump to the injection nozzles. The injection lines are pre-bent for correct routing and connect to the injection pump head as shown in the figure above. The injection lines are equal in length and interior volume.

Fuel Metering

The fuel metering is accomplished by the fuel solenoid driver by using the signals from the PCM in order to control the fuel injection solenoid.

Injection Timing

The injection timing stepper motor advances or retards the injection timing by the signals that are received from the PCM.

Engine Shutoff Solenoid

With the ignition on, the PCM completes the ground and activates ESO (allows fuel to flow into the transfer pump). When not activated by the PCM, the engine shutoff solenoid blocks the fuel flow from entering the transfer pump and stops the engine from operating.