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| Illustration 1 | g02408599 |
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(1) Secondary fuel filter base with two 4 micron fuel filters
(2) Common rail for fuel supply in cylinder head (3) Mechanical Electronic Unit Injector (MEUI) (4) Return fuel pressure regulator (6) Diverter actuator (7) Electric priming pump (8) Primary fuel filter base (9) Fuel tank (10) 1900 kPa fuel pressure regulator (11) Primary fuel filter with water separator (12) Fuel transfer pump (13) Speed sensor (14) Pressure sensor (15) Battery (16) Temperature sensor (17) Timing calibration connector (18) Throttle position sensor (19) Level sensor (20) SAE J1939 Data Link (21) Electronic Control Module (ECM) (22) Warning lamp (23) Diagnostic lamp (24) Programmable outputs (25) PTO SET/RESUME switch (26) Power Take Off (PTO) ON/OFF switch (27) Keyswitch | |
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 mechanical 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.
There are six major components of the MEUI fuel system:
- Mechanical electronic unit injectors
- Fuel transfer pump
- ECM
- Sensors
- Solenoids
- Camshaft
The MEUI produces fuel injection pressures up to
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| Illustration 2 | g02408619 |
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(1) Secondary fuel filter
(2) Common rail in cylinder head (3) Mechanical Electronic Unit Injector (MEUI) (4) Return fuel pressure regulator (6) Diverter actuator (7) Electric priming pump (8) Primary fuel filter base (9) Fuel tank (10) 1900 kPa fuel pressure regulator (11) Primary fuel filter and water separator (12) Fuel transfer pump | |
The low-pressure fuel system supplies fuel from the fuel tank to the injectors. The low-pressure fuel system has four basic functions:
- Supply fuel for combustion
- Supply fuel in order to cool the injectors.
- Remove air from the fuel.
- Warm the fuel in the fuel tank.
The major parts in a low-pressure fuel system consist of the following components:
- Fuel tank
- Fuel transfer lines
- Primary fuel filter or water separator
- Fuel transfer pump
- Secondary fuel filter
- Fuel priming pump
- Return fuel pressure regulator
The mechanical electronic unit injectors, the fuel transfer pump, the ECM, sensors, and solenoids are part of the low-pressure fuel system.
In the low-pressure fuel system, the fuel is pulled from the fuel tank to the primary fuel filter or to the water separator. The primary fuel filter (11) removes debris from the fuel that is larger than 10 microns before the fuel flows into the fuel transfer pump (12). The fuel transfer pump is a gear pump that contains a pressure relief valve . The pressure relief valve opens at approximately 60 to 125 PSI. Fuel then flows from the outlet port of the fuel transfer pump to the secondary fuel filters. The 4 micron filters remove small abrasive contaminants from the fuel system, which can damage the unit injectors.
The primary fuel filter base (8) contains an electric priming pump (7). The electric priming pump forces the air out of the system through the orifice on the regulator. Priming usually takes place after servicing the fuel system such as the changing of the fuel filter. When air is trapped in the fuel filters, the fuel lines, and other fuel system components, the engine could be difficult to start. This problem can also occur when the engine has not run for a long time. When there is air in the fuel line, the electric priming pump is activated by flipping a switch or by turning the start switch, in order to prime the system. The length of time for priming the fuel system depends on the size of the system, the length of the fuel line, and the size of the filter. The time that is needed in order to prime the fuel system is about 30 seconds. This value varies with different applications.
The primary fuel filter base also contains a check valve that prevents reverse flow during priming.
The return fuel pressure regulator (4) consists of a check valve that is spring loaded. 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 head maintains a supply of fuel for the injectors during start-up.
The ECM controls major engine functions. Sensors are electronic devices that monitor the parameters of engine performance. The pressure sensor, the temperature sensor, and the speed sensor 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.
The electronic control 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. 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 rpm. 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 RPM 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 engine control portion of the vehicle harness. The engine control portion includes the following components.
- Transmission
- Brake
- Clutch switches
- PTO switch
- Data links
- Check engine light
- Warning light
- Engine retarder switch
- Speedometer
- Tachometer
- Cooling fan solenoid
The features in the following list 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, less smoke, faster cold starting and built-in engine protection.
The ECM 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 curves
- Rpm
- Other characteristics
The ECM, the personality module, the sensors, and the unit injectors work together in order to control the engine. The ECM, the personality module, the sensors, and the unit injectors cannot control the engine alone.
The ECM determines a desired rpm that is based on the following criteria:
- Throttle signal
- Certain diagnostic codes
- Vehicle speed signal
The ECM maintains the desired engine rpm by sensing the actual engine rpm. The ECM calculates the fuel amount that needed in order to achieve the desired rpm.
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| Illustration 3 | g01944393 |
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Typical examples of electronic unit injector fuel systems. (28) Unit injector (29) Adjusting nut (30) Rocker arm assembly (31) Pushrod (32) Camshaft | |
The unit injector (28) pressurizes the fuel. The correct amount of fuel is then injected into the cylinder block 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 (32) through the lifter to the pushrod (31). The force of the pushrod is transferred through the rocker arm assembly (30) and to the top of the unit injector. The transferred force pushes the plunger in the top of the injector downward. The movement of the plunger injects fuel into the cylinder. The adjusting nut (29) 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.
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| Illustration 4 | g01887475 |
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(33) Tappet
(34) Plunger (35) Barrel (36) Solenoid (A) Nozzle assembly | |
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 (36) is energized. The ECM sends a 90 V signal to the solenoid in order to energize the solenoid. By controlling the timing of the 90 V signal, the ECM controls injection timing. By controlling the duration of the 90 V signal, the ECM controls the injected fuel amount.
Injection timing is determined by engine rpm, and other engine data. 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.