834985 Mercruiser GROMMET

Illustration 1 g00418398
Fuel System Schematic (1) Fuel filter base (2) Siphon break (3) Vent plug (4) Unit injectors (5) Fuel supply manifold (6) Drain plug (7) Fuel priming pump (8) Fuel return manifold (9) Secondary fuel filter (10) Fuel regulator valve (11) Fuel return port (12) Electronic control module (ECM) (13) Fuel transfer pump (14) Pressure regulating valve (15) Check valve (16) Fuel tankThe fuel supply circuit is a conventional design for unit injector diesel engines. Fuel transfer pump (13) is a gear type pump. The clearance in the fuel transfer pump is constant. The fuel transfer pump delivers fuel from the tank to unit injectors (4). Fuel is pulled from the fuel tank by the fuel transfer pump. The fuel transfer pump incorporates check valve (15) in order to allow fuel flow around the gears for hand priming. Pressure regulating valve (14) is used to protect the system from extreme pressure. The fuel transfer pump creates excess fuel flow that cools the unit injectors. The excess fuel flow also purges the air from the unit injectors. After the fuel transfer pump, the fuel flows through the cored passages in the electronic control module housing in order to cool the module. The fuel then flows through secondary fuel filter (9). Fuel priming pump (7) is located on the fuel filter base. The fuel priming pump is used to fill the system after draining the fuel supply and return manifolds. Fuel filter base (1) also incorporates siphon break (2) in order to prevent fuel from exiting the cylinder head during long periods of storage. Fuel priming pump (7) minimizes the fuel that returns to the tank by utilizing two check valves. The fuel flows continuously from the fuel supply manifold through the unit injectors and excess fuel is returned to the tank by fuel return manifold (8). The plunger displaces some fuel that is not injected into the cylinder. This fuel is also returned to the tank by the fuel return manifold. Refer to Systems Operation/Testing and Adjusting, "Unit Injector" for an explanation of the injection process.A flow control orifice is located in the fuel return manifold. The flow control orifice maintains sufficient system back pressure in order to fill the unit injectors. Superb fuel flow is provided to the unit injectors without excessive heating of the fuel tank. Fuel transfer pump (13) is located at the left front lower corner of the engine. The fuel transfer pump is driven by the lower accessory drive gear. The fuel supply and return manifolds are drilled passages in a common manifold which is mounted to the cylinder head. Fuel from fuel supply manifold (5) flows through drilled passages in the cylinder head, and into unit injectors (4). Fuel return port (11) is located at the end of fuel return manifold (8). The fuel return port is a part of fuel filter base (1). The pressure regulating orifice maintains the needed back pressure in order to fill the unit injectors. The pressure regulating orifice also provides a constant fuel flow through the unit injectors. Fuel System Electronic Control Circuit
Illustration 2 g00549482
Logic for Engine Speed Control (A) Coolant temperature sensor (B) Cold mode operation (C) Logic for engine control (D) Customer parameters (E) Throttle position sensor (1) Engine speed in rpm (2) Desired RPM (3) Transmission clutch/brake pedal
Illustration 3 g00549489
Electronic Governor (A) Fuel injection control (B) Electronic governor (C) FRC maps (D) Torque maps (E) Atmospheric pressure sensor (F) Coolant temperature sensor (G) Fuel temperature sensor (H) Fuel pressure sensor (I) Engine speed signal interpreter (J) Boost pressure sensor (K) Engine speed sensor (1) Signals to unit injectors (2) Fuel position (3) Desired RPM (4) Engine RPM (5) FRC fuel position (6) Rated fuel position (7) Atmospheric pressure (8) Coolant temperature (9) Fuel temperature (10) Fuel pressure (11) Top center for No. 1 cylinder (12) Boost pressureThe following traditional Caterpillar fuel system components have been replaced with an electronically controlled, mechanically actuated unit injector in each cylinder.
Fuel injection pump
Fuel injection lines
Fuel injector nozzlesA solenoid on each unit injector controls the amount of fuel that is delivered by the unit injector. The Electronic Control Module (ECM) sends a signal to each unit injector solenoid in order to provide complete control of the engine.Electronic Controls
The electronic control system for the engine consists of two main components:
Electronic Control Module (ECM)
Personality ModuleThe ECM is the computer. 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 characteristicsThe ECM, the personality module, the sensors, and the unit injectors work together in order to control the engine. Neither of the four can control the engine alone.The ECM determines a desired rpm that is based on the following criteria:
Throttle signal
Certain diagnostic codes
Vehicle speed signalThe ECM maintains the desired engine rpm by sensing the actual engine rpm. The ECM calculates the fuel amount that needs to be injected in order to achieve the desired rpm.Fuel Injection
The ECM controls the amount of fuel that is injected by varying the signals to the unit injectors. The unit injectors will inject fuel ONLY if the unit injector solenoid is energized. The ECM sends a 90 volt signal to the solenoid for energizing the solenoid. By controlling the timing of the 90 volt signal, the ECM can control injection timing. By controlling the duration of the 90 volt signal, the ECM can control the amount of fuel that is injected.The ECM sets certain limits on the amount of fuel that can be injected. FRC Fuel POS is a limit that is based on boost pressure in order to control the fuel air mixture for the emission control. When the ECM senses an increase in the boost pressure, the ECM increases the FRC Fuel POS. Rated Fuel POS is a limit that is based on the horsepower rating of the engine. Rated Fuel POS is similar to the rack stops and the torque spring on a mechanically governed engine. Rated Fuel POS