(1) Electronic unit injector
(2) Heat exchanger
(3) Cylinder heads
(4) Fuel tank
(5) Primary fuel filter and water separator
(6) Fuel transfer pump
(7) Electronic Control Module (ECM)
(8) Fuel priming pump and secondary fuel filter
Note: The fuel cooler is part of the heat exchanger. , The fuel cooler is optional on Tier I engines with prefixes (S/N: RNC) and (S/N: T3T). The fuel cooler is standard for Tier II engines that are rated pleasure craft with the prefixes (S/N: RNR) and (S/N: RNZ).
The fuel supply circuit is a conventional design for unit injector diesel engines. The system consists of the following major components that are used to deliver low pressure fuel to the unit injectors:
Fuel tank - The fuel tank is used to store the fuel.
Fuel priming pump - The fuel priming pump is used to evacuate the air from the fuel system. As the air is removed the system fills with fuel.
Fuel filters - The primary fuel filter is used to remove abrasive material and contamination from the fuel system that may be large enough to damage the fuel transfer pump. The secondary fuel filter is used to remove abrasive material and contamination as small as two microns that could damage the injectors.
Supply lines and return lines - Supply lines and return lines are used to deliver the fuel to the different components.
The purpose of the low pressure fuel supply circuit is to supply fuel that has been filtered to the fuel injectors at a rate that is constant and a pressure that is constant. The fuel system is also utilized to cool components such as the fuel injectors and the Electronic Control Module (ECM).
Once the injectors receive the low pressure fuel, the fuel is pressurized again before the fuel is injected into the cylinder. The unit injector uses mechanical energy that is provided by the camshaft to achieve pressures that can be in excess of
Control of the fuel delivery is managed by the engine's ECM. Data from several of the engine systems is collected by the ECM and processed in order to manage these aspects of fuel injection control:
- Injection timing
- Fuel injection timing advance
- Injection duration
- Engine cold mode status
The mechanical electronic fuel system relies on a large amount of data from the other engine systems. The data that is collected by the ECM will be used in order to provide optimum performance of the engine.
The flow of fuel through the system begins at fuel tank (4). Fuel is drawn through the primary fuel filter and water separator (5) from the fuel tank by fuel transfer pump (6). The fuel transfer pump incorporates a check valve that will allow fuel to flow around the gears of the pump during priming of the fuel system. The fuel transfer pump also incorporates a pressure relief valve. The pressure relief valve is used in order to protect the fuel system from extreme pressure.
The fuel transfer pump is designed in order to produce an excess fuel flow throughout the fuel system. The excess fuel flow is used by the system to cool the fuel system components. The excess fuel flow also purges any air from the fuel system during operation. Air that can become trapped in the fuel system can cause cavitation that may damage the components of the unit injector.
After leaving the fuel transfer pump, the fuel flows to the ECM in order to cool the ECM. Next, the fuel flows to the secondary fuel filter and fuel priming pump (8). The fuel priming pump is located on the fuel filter base. The fuel filter base and the secondary fuel filter also incorporate a siphon break that prevents fuel from draining from the fuel system when the engine is not in operation. The priming pump is a hand operated pump that directs the flow of fuel during the priming pump's operation. The secondary fuel filter is a two micron fuel filter. The fuel is filtered in order to remove small abrasive particles that will cause premature wear to fuel system components. The filtered fuel then flows out of the fuel filter and returns to the passages in the fuel filter base. Prior to exiting the fuel filter base, the fuel pressure and the fuel temperature are sampled by the fuel pressure sensor and by the fuel temperature sensor. The signals that are generated by the sensors are used by the ECM in order to monitor the condition of the engine's components. This information is also used to adjust the fuel delivery of the engine in order to optimize efficiency.
After leaving the secondary fuel filter, the fuel flows to the heat exchanger (2) in order to be cooled. Some engines may not be equipped with a heat exchanger that cools the fuel. The fuel is then transfered by the fuel supply lines to the cylinder head (3). Only a portion of the fuel that is supplied to the fuel injectors is used for engine operation. This unused fuel is discharged into the return passages of the fuel gallery. The fuel is returned to the fuel tank by the fuel return lines. A continuous flow of fuel is experienced within the low pressure fuel system.
During engine operation, fuel injectors (1) receive fuel from the low pressure fuel system. The injector pressurizes the fuel to high pressure. The fuel is then injected into the cylinder. The excess fuel is returned to the tank.
A pressure regulating valve is located in the fuel return. The pressure regulating valve allows the low pressure fuel system to maintain a constant pressure. A flow control orifice is also located in the fuel return. The flow control orifice maintains a system back pressure that is constant. The orifice allows the flow of fuel through the system to be constant. This prevents excessive heating of the fuel.
Fuel heaters prevent the waxing of the fuel, and the plugging of the fuel filters in cold weather. The engine does not dissipate enough heat in order to prevent waxing during cold weather conditions. There are two types of fuel heaters that can be used: thermostatically controlled and self-adjusting. Heaters that are not thermostatically controlled can heat the fuel in excess of
- Reduced engine efficiency
- Fuel pump damage
- Premature wear
Note: Never use fuel heaters without some type of temperature regulator. Ensure that fuel heaters are turned OFF during warm weather conditions.
The fuel system is equipped with an electronically controlled, mechanically actuated electronic unit injector in each cylinder. A solenoid on each injector controls the amount of fuel that is delivered by the injector. An ECM sends a signal to each injector solenoid in order to provide complete control of the engine.
There are two major components of the electronic control system that are necessary in order to provide control of the mechanical electronic unit injectors:
- Personality module (storage for the ECM flash file)
The ECM is the computer that is used to provide control for all aspects of engine operation. The personality module contains the software that defines the characteristics of the engine control. The personality module contains the operating maps. The operating maps define the following characteristics of the engine:
- Torque curves
- Engine speed (rpm)
- Other characteristics
The ECM, the personality module, the engine sensors, and the unit injectors work together in order to control the engine. Neither of the four can control the engine alone.
The ECM maintains the desired engine speed by sensing the actual engine speed. The ECM calculates the amount of fuel that needs to be injected in order to achieve the desired engine speed.
The ECM controls the amount of fuel that is injected by varying the signals that are sent to the injectors. The ECM sends a high voltage signal to the solenoid in order to energize the solenoid. The injectors will inject fuel only while the injector solenoid is energized. By controlling the timing and the duration of the high voltage signal, the ECM can control injection timing and the amount of fuel that is injected.
The ECM sets certain limits on the amount of fuel that can be injected. The Fuel Ratio Control (FRC) limit is an adjustment which controls the amount of air and of fuel for the purpose of emission control. This limit is based on the boost pressure. When the ECM senses a higher boost pressure, the ECM increases the FRC limit. The rated fuel position is also a limit that is based on the horsepower rating of the engine. This is similar to the rack stops and to the torque spring on a mechanically governed engine. The rated fuel position provides horsepower and torque curves for a specific engine family and for a specific engine rating. All of these limits are programmed into the personality module by the factory. These limits are not programmable by the service technician.
Injection timing depends on three factors: the engine speed (rpm), the engine load and the operational conditions of the engine. The ECM determines the top center position of No. 1 cylinder from the signal that is provided by the engine speed/timing sensor. The ECM decides when the injection should occur relative to the top center position. The ECM then provides the signal to the electronic unit injector at the desired time.
Electronic unit injector mechanism
(9) Electronic unit injector
(10) Adjusting nut
(11) Rocker arm assembly
(12) Camshaft lobe
The electronic unit injector mechanism provides the downward force that is required to pressurize the fuel in the electronic unit injector pump. The electronic unit injector (9) allows fuel to be injected into the combustion chamber with precise timing. Movement is transmitted from the camshaft lobe (12) for the electronic unit injector through the rocker arm assembly (11) to the top of the electronic unit injector. The adjusting nut (10) allows the injector lash to be adjusted. For the proper setting of the injector lash, refer to the topic on adjustment of the electronic unit injector in Testing and Adjusting, "Electronic Unit Injector - Adjust".
Electronic unit injector
(14) Solenoid connection to the Electronic Control Module (ECM)
(15) Solenoid valve assembly
(16) Plunger assembly
(23) 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 (13) is compressed and plunger (16) is driven downward. This action displaces fuel through the valve in solenoid valve assembly (15), and into the return manifold to the fuel tank. As the plunger travels downward, the passage in barrel (17) is closed by the outside diameter of the plunger. The passages within body (22) and along check valve (23) 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 Electronic Control Module (ECM).
When the solenoid valve assembly is energized from a signal across solenoid connection (14), the valve closes and fuel pressure is elevated in the injector tip. Injection begins at
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.