Mercury MerCruiser D2.8L D-Tronic Service Manual page 495

SERVICE MANUAL NUMBER 22
INJECTOR TIMING REGULATION
Determining the proper fuel injection point (timing) depends on the quantity of fuel, engine
rpm and coolant temperature. The ECM controls the timing using the signal from the number
one instrumented injector and corrects the timing to the nominal timing rate. Timing is
changed by modulating the pressure in the upper (high pressure) chamber communicating
with the pump body through the Timing Solenoid Valve.
During operation, the fuel pressure in the pump upper chamber exerts pressure on the
injection timing actuator piston. The piston has a spring on the lower side which, along with
the pressure chamber, allows the piston to maintain a regulated pressure in the upper
chamber that the ECM can monitor and adjust.
The Timing Solenoid Valve is operated by the ECM. The ECM will adjust the pressure in the
upper chamber to the level that provides the required timing and discharges the excess
pressure into the lower chamber. From the lower chamber, the excess fuel is returned to the
tank. The position of the Timing Solenoid Valve piston is actually determined by the
difference in the pressure acting on the face of the piston. The position of the injection timing
adjustment piston also determines the position of the piston in its valve seat. Rotating the
bearing ring changes the piston valve seat phasing compared to the position of the rotating
cam disk. This advances the intake phase. With the valve open, the injection is delayed.
Reducing the inlet orifice by closing the valve, advances the timing based on the resulting
pressure drop. The solenoid is closed if power (12 v) is removed.
NOTE: The electronic injection pump is not serviceable. If a pump needs service, consult
your Mercury MerCruiser Dealer or the nearest Bosch Dealer Service Network office.
ENGINE SHUT OFF
The principle of auto-ignition as applied to the diesel engine means that the engine can only
be switched off by interrupting its supply of fuel.
When equipped with Electronic Diesel Injection control, the engine is switched OFF by the
Fuel Quantity Actuator (an input signal from the ECM: injected fuel quantity = zero). The Fuel
Shut Off Valve, a separate electrical engine shut off device on the fuel pump, serves as a
standby shut off in case the actuator should fail.
90-860074--1 FEBRUARY 2002
DESCRIPTION
Page 5A-29