17650-921-003ZB Honda SEE PART DETAILS - PRI; CONNECTOR, FUEL *NH1* (Honda Code 2920890). (BLACK)

Illustration 1 g01915500
(1) Fuel filter base
(2) Temperature sensor
(3) Fuel pressure sensor (secondary filter inlet)
(4) Fuel pressure sensor (secondary filter outlet)
(5) Cylinder head
(6) Fuel injector
(7) Low-pressure regulator
(8) Fuel tank
(9) Electric priming pump
(10) Primary fuel filter
(11) Fuel transfer pump
(12) Electronic control module (if equipped) The fuel supply circuit is a conventional design for electronic unit injector diesel engines. Fuel transfer pump (11) of the circuit is a gear-type pump with positive displacement. The fuel transfer pump is located in the front of the engine at the lower left corner. The fuel transfer pump is mounted to the front timing gear cover. The fuel transfer pump is driven by the front gear train.The fuel transfer pump draws fuel from fuel tank (8). The fuel passes through primary filter/water separator (9). The fuel passes into the fuel transfer pump and the fuel is then pressurized. The fuel transfer pump incorporates a check valve in order to permit a fuel flow around the gears for hand priming. The fuel transfer pump also incorporates a relief valve in order to protect the system from extreme pressure. The excess fuel flow that is provided by the fuel transfer pump is used in order to cool the electronic unit injectors. The excess fuel flow also purges the air from the fuel system.The fuel from the fuel transfer pump flows through the fuel filter at fuel filter base (1). Fuel temperature sensor (2) is mounted in the fuel filter base. The Engine Control Module (ECM) (12) uses the sensor to monitor the temperature of the fuel that is entering the engine. The information is used by the ECM to calculate a fuel correction factor during engine operation. Fuel priming pump (8) is positioned on the fuel filter base in order to prime the system when air has been introduced into the fuel system. For more information on priming the fuel system, refer to Testing and Adjusting, "Fuel System - Prime".The fuel leaves the fuel filter base and flows through the fuel supply line to the cylinder head. The fuel enters the cylinder head at the front of the engine. Fuel is delivered to the electronic unit injectors through fuel manifold that is drilled into the cylinder head during the manufacturing process.Excess fuel exits the cylinder head at the rear. The fuel returns to the fuel filter base through the fuel return line to the pressure regulating valve that is incorporated into the fuel filter base. The pressure regulating valve maintains a sufficient amount of back pressure in the system in order to fill the electronic unit injectors. After the fuel passes through the pressure regulating valve, the fuel returns to the fuel tank. The fuel flows continuously from the fuel supply through the electronic unit injectors in the head and back to the tank.Fuel System Electronic Control Circuit
The injection pump, the fuel lines, and the nozzles that are used in the traditional Caterpillar diesel engines have been replaced with a mechanically actuated electronically controlled unit injector in each cylinder. The engine has two solenoids on each injector that controls the amount of fuel that is delivered by the injector. The ECM sends a signal to each injector solenoid in order to provide complete control of the fuel to the engine.Electronic Controls
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.Fuel Injection Timing and Delivery
This engine uses an injection system control that allows variable control of the spray pattern of the injector during the duration of fuel injection into the cylinder. A pilot injection takes place in order to start fuel combustion in the cylinder. When the pilot injection has been completed, the fuel injection delivery is then controlled by the ECM in order to optimize the combustion efficiency for the current operating conditions. The pilot injection requires a new camshaft with a modified injector lobe.The ECM controls the amount of the fuel that is injected by varying the signals to the electronic unit injectors. The electronic unit injectors will inject fuel only if the electronic unit injector solenoid is energized. The ECM sends 120 VDC to the solenoid in order to energize the solenoid. By controlling the timing of the 120 V signal, the ECM can control injection timing. By controlling the duration of the 120 V signal, the ECM can control the injected fuel amount.The ECM sets certain limits on the amount of fuel that can be injected. The Fuel Ratio Control FRC fuel position is a limit that is based on boost pressure in order to control the air/fuel mixture for the emission control. When the ECM senses an increase in the boost pressure, the ECM increases the FRC fuel position. The rated fuel position is a limit that is based on the horsepower rating of the engine. The rated fuel position is similar to the rack stops and the torque spring on a mechanically governed engine. The rated fuel position provides the horsepower and the torque curves for a specific horsepower rating. The limits are programmed by the factory into the personality module.Injection timing depends on three factors: the engine speed, the engine load and other engine data. The ECM determines the top center position of cylinder number 1 from the signal that is provided by the crankshaft position sensor. The ECM determines when the fuel injection should occur relative to the top center