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| Illustration 1 | g01119154 |
(1) Injectors (2) Fuel priming pump and fuel filter (3) Fuel pump (4) Electronic Control Module (ECM) (5) Fuel supply rail (6) Fuel tank (7) Fuel pressure regulator (8) Injector wiring (9) Primary fuel filter and water separator | |
The Electronic Unit Injector system consists of the following systems: the mechanical system and the electronic system. The mechanical system is made up of the low pressure fuel supply system and the electronic unit injectors. The electronic system provides complete electronic control of all engine functions. The electronic control system consists of the following three types of components: input, control and output.
Most changes to engine horsepower or to the performance are accomplished by installing new electronic software or upgrading mechanical components.
There are five major components of the Electronic Unit Injector fuel system:
- Electronic unit injectors
- Fuel transfer pump
- Electronic Control Module (ECM)
- Sensors
- Actuators
The electronic unit injectors produce fuel injection pressures up to 207000 kPa (30000 psi). The electronic unit injectors also fire up to 19 times per second at rated speed. The fuel transfer pump supplies the injectors by drawing fuel from the tank and by pressurizing the fuel manifold between 60 and 125 PSI. The ECM is a powerful computer which controls all major engine functions. Sensors are electronic devices which monitor the engine performance. Examples of engine performance that are monitored are pressure, temperature and speed. This information is sent to the ECM via a signal voltage. Actuators are electronic devices which use electrical currents from the ECM to change engine performance. An example of an actuator is the injector solenoid.
Low Pressure Fuel System
The low pressure fuel system supplies fuel from the fuel tank to the injectors. The low pressure fuel system has three basic functions:
- The low pressure fuel system supplies fuel to the injectors for combustion.
- The low pressure fuel system supplies fuel to the injectors for cooling.
- The low pressure fuel system supplies fuel to the ECM for cooling.
- The low pressure fuel system supplies fuel to the fuel system in order to remove air.
- The low pressure fuel system removes water from the fuel system.
The major parts in a low pressure fuel system consist of the following components:
- Fuel tank
- Fuel transfer lines
- Fuel transfer pump
- Primary fuel filter and water separator
- Fuel priming pump and secondary fuel filter
- Fuel pressure regulator valve
The electronic unit injectors, the ECM, the sensors, and the actuators are also part of the low pressure fuel system.
In the low pressure fuel system, the fuel is pulled from the fuel tank through the primary fuel filter and the water separator. The fuel is then pulled through the ECM in order to cool the ECM. Then, the fuel flows to the fuel transfer pump. The fuel transfer pump is a gear pump that contains a pressure relief valve. Fuel flows from the outlet port of the transfer pump to the secondary fuel filter and fuel priming pump. All 1999 and newer engines use a 2 micron fuel filter. The 2 micron filter removes small abrasive contaminants from the fuel system, which can cause damage to the unit injectors.
The fuel filter base contains a hand operated fuel priming pump. The fuel priming pump removes air from the system when a fuel filter has been changed or a unit injector has been changed. The priming pump pulls fuel from the tank, around the transfer pump and into the filter. The transfer pump pushes fuel through the supply passage in the cylinder head and back to the tank. This removes any air that is trapped in the system.
The fuel pressure regulator consists of a check valve that is spring loaded. The pressure relief valve opens at approximately 60 to 125 PSI. When the engine is in the off position and the fuel pressure drops below 60 PSI, the check valve closes. The check valve closes in order to prevent the fuel in the cylinder head from draining back into the fuel tank. Retaining the fuel in the cylinder head maintains a fuel supply for the injectors during start procedures.
The electronic control module controls major engine functions. Sensors are electronic devices that monitor the engine performance. Pressure sensors, temperature sensors, and speed sensors provide information to the ECM by a signal voltage. Actuators are electronic devices which use electrical currents from the ECM to change engine performance. An example of an actuator is an injector solenoid.
Electronic Controls
The electronic control system provides complete electronic control of all major engine functions. The electronic control system consists of the following three types of components: input, control and output. Sensors monitor engine operating conditions. This information is sent to the ECM. The ECM has three main functions. The ECM provides power for the engine electronics and monitors input signals from the engine sensors. The ECM also acts as a governor to control engine speed. The ECM stores active faults, logged faults, and logged events. The personality module is the software in the ECM which contains the specific maps that define power, torque, and speed of the engine. The ECM sends electrical current to the output components in order to control engine operation. The ECM has the following connectors: two 70 pin harness connectors, one engine harness connector and one vehicle harness connector. The vehicle harness connects the ECM to the portion of the vehicle harness that is for engine control.
The following list of features are part of the electronic control system:
- Cold start strategy
- Oil pressure
- Coolant temperature warning indicator
- Automatic altitude compensation
- Variable injection timing
- Electronic engine speed governing
These features result in the following items: precise engine speed control, emission control and built-in engine protection.
The electronic control module consists of the following two main components: the ECM and the personality module.
The ECM is a computer and the personality module is the software for the computer. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
- Horsepower
- Torque curve
- RPM limits
The ECM, the personality module, the sensors, and the unit injectors work together in order to control the engine. The ECM maintains the desired engine speed by comparing the actual speed and desired speed. The ECM adjusts the fuel delivery that needs to be injected in order to achieve the acceptable differences between actual engine speed and desired speed.
Fuel Injection Timing and Delivery
The ECM controls the injected fuel amount by varying the signals to the unit injectors. The unit injectors will inject fuel only if the unit injector solenoid is energized. The ECM sends a 90 volt signal to the solenoid for energizing the solenoid. By controlling the timing of the 90 volt signal, the ECM controls injection timing. By controlling the duration of the 90 volt signal, the ECM controls the injected fuel amount.
Injection timing is determined by engine speed, and load. The ECM senses the top center position of cylinder number 1 from the signal that is provided by the engine speed sensor. The ECM decides when the injection should occur relative to the top center position. The ECM provides the signal to the unit injector at the desired time.
Unit Injector Mechanism
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| Illustration 2 | g01119416 |
Electronic Unit Injector fuel system (1) Adjusting nut (2) Rocker arm assembly (3) Unit injector (4) Pushrod | |
Injection Actuation System
The unit injector pressurizes the fuel. The correct amount of fuel is then injected into the cylinder at precise times. The ECM determines the injection timing and the amount of fuel that is delivered. The unit injector is operated by a camshaft lobe and a rocker arm. The camshaft has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and the other lobe operates the unit injector mechanism. Force is transferred from the unit injector lobe on the camshaft through the lifter to the pushrod (4). The force of the pushrod (4) is transferred through rocker arm assembly (2) and to the top of the unit injector. The adjusting nut (1) allows setting of the unit injector adjustment. Refer to Systems Operation/Testing and Adjusting, "Electronic Unit Injector - Adjust" for the proper setting of the unit injector adjustment.
Unit Injector
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| Illustration 3 | g01119426 |
Electronic unit injector (1) Spring (2) Solenoid connection to the ECM (3) Solenoid valve assembly (4) Plunger assembly (5) Barrel (6) Seal (7) Seal (8) Spring (9) Spacer (10) Body (11) Check valve | |
Fuel at low pressure from the fuel supply manifold enters the electronic unit injector at the fill port through drilled passages in the cylinder head.
As the electronic unit injector mechanism transfers the force to the top of the electronic unit injector, spring (1) is compressed and plunger (4) is driven downward. This action displaces fuel through the valve in solenoid valve assembly (3), and into the return manifold to the fuel tank. As the plunger travels downward, the passage in barrel (5) is closed by the outside diameter of the plunger. The passages within body (10) and along check valve (11) to the injector tip already contain fuel for injection. After the passage in the plunger barrel is closed, the injector is ready for injection at any time. The start of injection relies on the software in the ECM.
When the solenoid valve assembly is energized from a signal across solenoid connection (2), the valve closes and fuel pressure is elevated in the injector tip. Injection begins as the force of spring (8) above spacer (9) is overcome. The check valve begins to lift from the valve seat. The pressure continues to rise as the plunger cycles through a full stroke. After the correct amount of fuel has been discharged into the cylinder, the ECM removes the signal to the solenoid connection. The solenoid valve assembly is de-energized and the valve in the solenoid valve assembly is opened. The high pressure fuel is then dumped through the spill port and into the fuel return manifold. The fuel is then returned to the fuel tank. The check valve in the injector tip seats as the pressure in the tip decreases.
The duration of injection meters the fuel that is consumed during the fuel injection process. Injection duration is controlled by the governor logic that is programmed into the ECM.
As the camshaft lobe rotates past the point of maximum lobe lift, the force on top of the electronic unit injector is removed and the spring for the injector mechanism is allowed to expand. The plunger returns to the original position. This uncovers the fuel supply passage into the plunger barrel in order to refill the injector pump body. The fuel at low pressure is again allowed to circulate through the fuel injector body. After circulating through the fuel injector body, the fuel flows out of the spill port. This continues until the solenoid valve assembly is re-energized for another injection cycle.