856583A 5 Mercury CABLE ASSEMBLY

Illustration 1 g06285934
Fuel system for C32 engines.
(1) Cylinder head
(2) Unit injector
(3) Fuel transfer pump
(4) Secondary fuel filter
(5) Primary fuel filter and water separator
(6) Fuel tank
(7) Fuel pressure regulator/check valveThe 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 filters - The primary fuel filter is used to remove abrasive material and contamination from the fuel system 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 and a pressure that is constant. The fuel system is also utilized to cool components such as the fuel injectors.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 more than 200000 kPa (30000 psi).Control of the fuel delivery is managed by the engine ECM. Data from several of the engine systems is collected by the ECM and processed to manage these aspects of fuel injection control:
Injection timing
Fuel injection timing advance
Injection duration
Engine cold mode statusThe 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 to provide optimum performance of the engine.Low-Pressure Fuel Supply Circuit
The flow of fuel through the system begins at fuel tank (5). Fuel is drawn through the primary fuel filter and water separator (7) from the fuel tank by fuel transfer pump (3). The fuel transfer pump incorporates a check valve that allows fuel to flow around the gears during priming. The fuel transfer pump also incorporates a pressure relief valve. The pressure relief valve is used to protect the fuel system from extreme pressure.The fuel transfer pump is designed 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 (6) to cool the ECM. Next, the fuel flows to the secondary fuel filter (4). The fuel filter base and secondary fuel filter incorporate a siphon break that prevents fuel from draining when the engine is not in operation. The secondary fuel filter is a two micron fuel filter. The fuel is filtered 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 are sampled by the fuel pressure sensor and fuel temperature sensor. The signals that are generated by the sensors are used by the ECM to monitor the condition of the engine components. This information is also used to adjust the fuel delivery of the engine to optimize efficiency.The fuel is then transferred by the fuel supply lines to the cylinder head (1). 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 (2) 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 consistency prevents excessive heating of the fuel.Fuel System Electronic Control Circuit
The fuel system is equipped with an electronically controlled, mechanically actuated 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 to provide complete control of the engine.There are two major components of the electronic control system that are necessary to provide control of the mechanical electronic unit injectors:
ECM
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:
Horsepower
Torque curves
Engine speed (rpm)
Other characteristicsThe ECM, the personality module, the engine sensors, and the unit injectors work together 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 injection needed to achieve the desired engine speed.Fuel Injection
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 to energize the solenoid. The injectors will inject fuel only while the injector solenoid is energized. By