3C7-76003-0 Tohatsu SPACER, 8.4 - 12 - 21.5

Illustration 1 g01061346
Fuel system schematic
(1) Fuel supply line
(2) Electronic unit injectors
(3) Fuel gallery
(4) Electronic Control Module (ECM)
(5) Fuel pressure sensor
(6) Fuel temperature sensor
(7) Pressure regulating valve
(8) Secondary fuel filter
(9) Fuel priming pump
(10) Fuel transfer pump
(11) Primary fuel filter
(12) Fuel tank The fuel supply circuit is a conventional design for engines with electronic unit injection. A fuel tank (12) is used to store the fuel prior to use by the engine. A primary fuel filter/water separator (11) is placed into the fuel supply circuit in order to remove large debris from the fuel. This debris may have entered the fuel tank during fueling. The debris may have also entered the fuel tank through the vent for the fuel tank. The primary filter element also separates water from the fuel. The water is collected in the bowl at the bottom of the primary fuel filter/water separator.Fuel is drawn from the fuel tank by the fuel transfer pump (10). The fuel transfer pump is a gear pump with fixed clearances. The fuel transfer pump incorporates an internal relief valve that protects the fuel system from extreme pressure. In the case of extreme pressure, fuel is redirected back to the inlet of the fuel transfer pump. There are internal check valves that are also incorporated into the fuel transfer pump. An inlet check valve prevents fuel from draining back to the fuel tank while the fuel transfer pump is not in operation. An outlet check valve is used in order to prevent pressurized fuel leakage back through the pump. The fuel transfer pump is located in the front of the engine. The fuel transfer pump is driven by the front gear train.Note: The inlet fuel temperature to the fuel transfer pump must not exceed 79 °C (175 °F) when the engine has reached normal operating temperature. Fuel temperatures above 79 °C (175 °F) will reduce the life of the fuel transfer pump check valves. The fuel efficiency and the engine power output are reduced when the fuel temperature increases from 30 °C (86 °F) to 70 °C (158 °F). The fuel heaters should be turned "OFF" during warm weather. Fuel from the fuel transfer pump flows to the fuel filter base. The fuel flows through cored passages in the fuel filter base. The fuel priming pump (9) is mounted on the fuel filter base. The fuel priming pump is used in order to manually pump the fuel into the fuel system after the system, or parts of the system have been drained. The fuel priming pump is used in order to refill the fuel system after air has been introduced into the system. For more information on priming the fuel system, refer to Testing and Adjusting, "Fuel System - Prime".As the fuel flows through cored passages in the fuel filter base, the fuel is directed into a 2 micron fuel filter (8). The fuel is filtered in order to remove small abrasive particles that will cause premature wear to fuel system components. Fuel 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 is sampled by the fuel pressure sensor (5) and by the fuel temperature sensor (6). The signals that are generated by the sensors are used by the engine control 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.The fuel flows from the fuel filter base to the Electronic Control Module (ECM) (4). The pressurized fuel is used in order to cool the electronic components that are in the ECM. Excessive heat will damage the electronic components in the ECM. The electronics are used to control engine operation. The fuel is then directed through the fuel supply line (1) to fuel manifold (3) that runs the length of the cylinder head. The fuel enters the cylinder head at the front of the engine. A continuous flow of fuel is supplied to the electronic unit injectors (2) in order to perform the following tasks:
Supply fuel for injection
Remove excessive heat from the injectors.
Remove air that may accumulate in the fuel system.The excess fuel flow that pumped through the system exits the cylinder head near the rear of the engine.The fuel exits the fuel gallery and returns to the fuel filter base. A pressure regulating valve (7) that is located in the fuel filter base regulates the pressure for the fuel system. A sufficient amount of back pressure is maintained in the system in order to ensure a continuous availability of fuel to the electronic unit injectors.Fuel Heaters
Fuel heaters prevent the waxing of the fuel in cold weather. The engine does not dissipate enough heat in order to prevent waxing during cold weather conditions. Heaters that are not thermostatically controlled can heat the fuel in excess of 65 °C (149 °F). High fuel temperatures can have the following effects:
Reduced engine efficiency
Fuel pump damage
Premature wearNote: Fuel heaters without thermostatic controls must never be used.The two types of fuel heaters that can be used: thermostatically controlled and self-adjusting.Electronic Controls
There are two major components of the electronic control system that are necessary in order 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 in order to control the engine. Neither of the four can control the engine alone. The ECM maintains