42725A 3 Mercruiser FUEL PUMP ASSEMBLY

Illustration 1 g06389637
Typical example
(1) In-line fuel filter
(2) Electric transfer pump
(3) Primary fuel filter
(4) ECM that is fuel cooled.
(5) Secondary fuel filter
(6) Fuel Injection Pump
(7) Inlet pressure regulator
(8) Fuel manifold (rail)
(9) Pressure relief valve
(10) Electronic unit injector
(11) Fuel cooler (optional)
(A) Fuel tankFuel is drawn from the fuel tank through an in-line fuel filter to an electric transfer pump. The fuel then flows to the 10 micron primary fuel filter/water separator.The fuel may flow to a fuel cooled ECM. The fuel then flows to a 4 micron secondary fuel filter.The fuel flows from the secondary fuel filter to a pressure regulator. A pressure regulator that is installed in the low-pressure fuel system controls the fuel pressure to the fuel injection pump. The pressure regulator regulates the fuel at an absolute pressure of 150 kPa (22 psi) when the engine is at idle speed.From the pressure regulator, the fuel flows to the fuel injection pump. The fuel is pumped at an increased pressure of 200 MPa (29000 psi) to the fuel manifold (rail).Fuel that has too high a pressure from the fuel manifold (rail) returns through the pressure relief valve to the return line. Fuel that is leak off from the electronic unit injectors flows to the return line. The fuel may then flow through an optional fuel cooler on the way back to the fuel tank.High Pressure Fuel System
Illustration 2 g02216334
Typical example
(1) Fuel injection pump
(2) Fuel temperature sensor
(3) Suction control valve for the fuel injection pump
(4) Pressure relief valve
(5) Electronic unit injector
(6) Fuel manifold (rail)
(7) Fuel pressure sensor
(8) Fuel transfer pumpThe fuel injection pump (1) feeds fuel to the high-pressure fuel manifold (rail) (6). The fuel is at a pressure of up to 200 MPa (29000 psi). A pressure sensor (7) in the high-pressure fuel manifold (rail) (6) monitors the fuel pressure in the high-pressure fuel manifold (rail) (6). The ECM controls a suction control valve (3) in the fuel injection pump (1) to maintain the actual pressure in the high-pressure fuel manifold (6) at the desired level. The high-pressure fuel is continuously available at each injector. The ECM determines the correct time for activation of the correct electronic unit injector (5) which allows fuel to be injected into the cylinder. The leakoff fuel from each injector passes into a drilling which runs along the inside of the cylinder head. A pipe is connected to the rear of the cylinder head to return the leakoff fuel to the fuel tank.Components of the Fuel Injection System
The fuel injection system has the following mechanical components:
In-line fuel filter
Primary filter/water separator
Electric transfer pump
Fuel transfer pump
Secondary fuel filter
Fuel injection pump
Fuel injectors
Fuel manifold
Pressure relief valve
Fuel pressure sensor
Fuel temperature sensor
Water in fuel sensorThe following list contains examples of both service and repair procedures after which you must prime the system:
A fuel filter is changed.
A low-pressure fuel line is replaced.
The fuel injection pump is replaced.
The ECM is replaced.
Draining water from the water separator.For the correct procedure to prime the fuel system, refer to Systems Operation, Testing and Adjusting, "Fuel System - Prime".Primary Filter/Water Separator
Illustration 3 g02214535
Typical example
The primary filter/water separator (1) is located between the electric transfer pump and the secondary fuel filter. The primary filter/water separator (1) provides a 10 micron filtration level.The primary filter/water separator can either be engine mounted or supplied loose. The primary filter/water separator is supplied with water in fuel sensor (2).Secondary Fuel Filter
Illustration 4 g02214536
Typical example
The secondary fuel filter (1) is located after the primary fuel filter. The secondary fuel filter (1) provides a 4 micron filtration level.Fuel Pump Assembly
Illustration 5 g02216343
Typical example
The fuel pump assembly consists of a low-pressure transfer pump and a high-pressure fuel injection pump. The pump assembly is driven from a gear in the front timing case at engine speed. The fuel injection pump (1) has three plungers that are driven by a camshaft. The fuel injection pump (1) delivers a volume of fuel three times for each revolution. The stroke of the plungers is fixed.The injector will use only part of the fuel that is delivered by each stroke of the pistons in the pump. The suction control valve (3) for the fuel injection pump (1) is controlled by the ECM. This valve maintains the fuel pressure in the fuel manifold (rail) at the correct level. A feature of the fuel injection pump (1) allows fuel to return to the tank continuously.The fuel temperature sensor (2) measures the temperature of the fuel. The ECM receives the signal from the fuel temperature sensor (2). The ECM calculates the volume of fuel.The fuel injection pump has the following operation:
Generation of high-pressure fuelThe fuel output of the fuel injection pump is controlled by the ECM in response to changes in the demand of fuel pressure.Shutoff
The engine shuts off by preventing the electronic unit injectors from injecting. The ECM then closes the suction control valve to prevent the pressure in the fuel manifold (rail) from increasing.Control
Illustration 6 g06370030
Typical example of the electrical control system for the fuel system
(1) Electronic Control Module (ECM)
(2) Throttle position sensor
(3) Wastegate regulator
(4) Fuel rail pressure sensor
(5) Inlet manifold pressure sensor
(6) Differential pressure sensor (NRS)
(7) Coolant temperature sensor
(8) Inlet manifold air temperature sensor
(9) Secondary speed/timing sensor