Fuel Injection System

FUEL INJECTION
Fuel Injection System
The Engine Control Module (ECM) and Fuel Injection Pump Control Module (FPCM) are used primarily for fuel system control. The ECM is a separate replaceable component, while the FPCM is internal to the fuel injection pump and is a non-serviceable part. The ECM and FPCM are interconnected (wired together) for fuel injection control.

The Powertrain Control Module (PCM) is used to regulate or control the A/C, charging and speed control systems. It is also used to partially control certain electronic automatic transmission components. The PCM also has control over certain instrument panel components.

Fig. 1 Fuel System Components:

Refer to either Powertrain Control Module (PCM) or Engine Control Module (ECM) for additional information. Refer to for a partial list of fuel system components.

Fig. 4 APPS Assembly Location:

Fig. 5 APPS Sensor Location (Rear View):

ACCELERATOR PEDAL POSITION SENSOR
The APPS assembly is located at the top-left-front of the engine. A plastic cover is used to cover the assembly. The actual sensor is located behind its mounting bracket.

The Accelerator Pedal Position Sensor (APPS) is a linear potentiometer. It provides the Engine Control Module (ECM) with a DC voltage signal proportional to the angle, or position of the accelerator pedal. In previous model years, this part was known as the Throttle Position Sensor (TPS).

These engines used in previous model years used a mechanical cable between the accelerator pedal and the TPS lever. Linkage and bellcranks between the TPS cable lever and the fuel injection pump were also used. Although the cable has been retained with the APPS, the linkage and bellcranks between the cable lever and the fuel injection pump are no longer used.

The APPS is serviced (replaced) as one assembly including the lever, brackets and sensor. The APPS is calibrated and permanently positioned to its mounting bracket.

CAUTION: Do not attempt to remove sensor from its mounting bracket as electronic calibration will be destroyed (sensor-to-bracket mounting screws are permanently attached). Two accelerator lever set screws are used to position lever. Do not attempt to alter positions of these set screws as electronic calibration will be destroyed.

FUEL INJECTOR

Fig. 10 Fuel Injector Location:

Six individual, high-pressure fuel injectors are used. The injectors are vertically mounted into a bored hole in the top of the cylinder head. This bored hole is located between the intake/exhaust valves.

High-pressure fuel is supplied from the injection pump, through a high-pressure fuel line, through a steel connector and into the fuel injector. When fuel pressure rises to approximately 31,026 kPa (4,500 psi), the needle valve spring tension is overcome. The needle valve rises and fuel flows through the spray holes in the nozzle tip into the combustion chamber. The pressure required to lift the needle valve is the nozzle opening pressure. This is sometimes referred to as the "pop" pressure setting.

Fig. 11 Fuel Injector Connections:

Each fuel injector is connected to each high-pressure fuel line with a steel connector. This steel connector is positioned into the cylinder head and sealed with an O-ring. The connectors are sealed to the high-pressure fuel lines with fittings. The ferrule on the end of the high-pressure fuel line pushes against the steel connector when the fuel line fitting is torqued into the cylinder head. This torquing force provides a sealing pressure between both the fuel line-to-connector and the fuel connector-to-fuel injector. The fitting torque is very critical. If the fitting is under torqued, the mating surfaces will not seal and a high-pressure fuel leak will result. If the fitting is over torqued, the connector and injector will deform and also cause a high-pressure fuel leak. This leak will be inside the cylinder head and will not be visible. The result will be a possible fuel injector miss-fire and low power.

Fig. 12 Fuel Injector Spray Pattern:

The fuel injectors use hole type nozzles. High-pressure flows into the side of the injector and causes the injector needle to lift and fuel to be injected. The clearances in the nozzle bore are extremely small and any sort of dirt or contaminants will cause the injector to stick. Because of this, it is very important to do a thorough cleaning of any lines before opening up any fuel system component.

Always cover or cap any open fuel connections before a fuel system repair is performed.

Fig. 13 Fuel Injector Edge Filter:

Each fuel injector connector tube contains an edge filter that breaks up small contaminants that enter the injector. The edge filter uses the injectors pulsating high-pressure to break up most particles so they are small enough to pass through the injector. The edge filters are not a substitute for proper cleaning and covering of all fuel system components during repair.

The bottom of each fuel injector is sealed to the cylinder head with a 1.5mm thick copper shim (gasket). The correct thickness shim must always be re-installed after removing an injector.

Fuel pressure in the injector circuit decreases after injection. The injector needle valve is immediately closed by the needle valve spring and fuel flow into the combustion chamber is stopped. Exhaust gases are prevented from entering the injector nozzle by the needle valve.

FUEL INJECTION PUMP RELAY
The fuel injection pump relay is located in the Power Distribution Center (PDC). Refer to label under PDC cover for relay location.

The Engine Control Module (ECM) energizes the electric fuel injection pump through the fuel injection pump relay. Battery voltage is applied to the fuel injection pump relay at all times. When the key is turned ON, the relay is energized when a 12-volt signal is provided by the ECM. When energized, 12-volts is supplied to the Fuel Pump Control Module. The Fuel Pump Control Module is located on the top of the fuel injection pump and is non-serviceable.

FUEL TEMPERATURE SENSOR
Two different fuel temperature sensors are used. One of the sensors is located inside of the Bosch VP44 fuel injection pump and is a non-serviceable part. The other fuel temperature sensor is located in the top of the fuel filter housing and is serviceable (serviceable if replacing the fuel heater).

The sensor located in the Bosch VP44 fuel injection pump is used to check fuel temperature within the injection pump and to set a Diagnostic Trouble Code (DTC) if a specific high fuel temperature has been reached. If high temperature has been reached, engine power will be de-rated by the Engine Control Module (ECM).

The sensor located in the top of the fuel filter housing is used to control the fuel heater element. Refer to Fuel Heater Description and Operation for additional information.

Fig. 25 Air Heater Elements Location:

INTAKE AIR HEATER
The intake manifold air heater element assembly is located in the top of the intake manifold.

The air heater elements are used to heat incoming air to the intake manifold. This is done to help engine starting and improve driveability with cool or cold outside temperatures.

Electrical supply for the 2 air heater elements is controlled by the Engine Control Module (ECM) through the 2 air heater relays. Refer to Intake Manifold Air Heater Relays for more information.

Two heavy-duty cables connect the 2 air heater elements to the 2 air heater relays. Each of these cables will supply approximately 95 amps at 12 volts to an individual heating element within the heater block assembly.

Refer to the Powertrain Diagnostic Procedures for an electrical operation and complete description of the intake heaters, including pre-heat and post-heat cycles.

Fig. 29 Intake Manifold Air Heater Relays Location:

INTAKE AIR HEATER RELAY
The 2 intake manifold air heater relays are located in the engine compartment, attached to the left inner fender below the left battery.

The Engine Control Module (ECM) operates the 2 heating elements through the 2 intake manifold air heater relays.

Refer to Powertrain Diagnostic Procedures for an electrical operation and complete description of the intake heaters, including pre-heat and post-heat cycles.

Fig. 31 Intake Manifold Air Temperature (IAT) Sensor Location:

INTAKE AIR TEMPERATURE SENSOR
The intake manifold air temperature sensor is installed into the rear of the intake manifold with the sensor element extending into the air stream.

The IAT provides an input voltage to the Engine Control Module (ECM) indicating intake manifold air temperature. The input is used along with inputs from other sensors for intake air heater element operation, for engine protection, fuel timing and fuel control. As the temperature of the air-fuel stream in the manifold varies, the sensor resistance changes. This results in a different input voltage to the ECM.

MAP SENSOR
The MAP sensor is installed into the rear of the intake manifold.

The MAP sensor reacts to air pressure changes in the intake manifold. It provides an input voltage to the Engine Control Module (ECM). As pressure changes, MAP sensor voltage will change. The change in MAP sensor voltage results in a different input voltage to the ECM. The ECM uses this input, along with inputs from other sensors to provide fuel timing, fuel control and engine protection. Engine protection is used to derate (drop power OFF) the engine if turbocharger pressure becomes to high.

PTO SWITCH
This Engine Control Module (ECM) input is used only on models equipped with aftermarket Power Take OFF (PTO) units.

The input is used to tell the ECM that the PTO has been engaged. When engaged, the ECM will disable certain OBD II functions until the PTO has been turned OFF.