Mercury MerCruiser D2.8L D-Tronic Service Manual page 494

DESCRIPTION
ENGINE SPEED CHANGES
The ECM adjusts the engine operating strategy during acceleration and deceleration in
order to avoid unstable operating conditions such as jerkiness and roughness.
FUEL FLOW PROPORTIONING
The ECM uses information from the Throttle Position sensor and the Engine rpm Speed
sensor along with the strategies in its memory to determine the proper fuel quantity to be
injected into the engine. After comparing the nominal position on the control collar with the
actual position of the control collar, a fuel quantity adjustment is made based on the fuel
temperature detected by the sensor on the pump. The adjustment will be made until the
actual position of the control collar coincides with its nominal position.
In this way the quantity of fuel appropriate for the selected operating conditions is delivered.
The maximum flow rate of the fuel is determined by engine rpm. The flow rate adjustment
also takes into account the input information detected by the ECM from the engine coolant
temperature sensor and the air intake temperature sensor. The ECM also handles an
engine operation control function, particularly during acceleration and deceleration.
ELECTRONIC INJECTION PUMP
The electronic injection pump with its upper chambers (high pressure) and lower chamber
(low pressure) pump and actuators are the same as the mechanically controlled injector
pump.
The pump interior pressure is dependent upon pump speed. Similar to the mechanical
timing device, this pressure is applied to the timing-device piston. This pressure on the
timing-device pressure side is modulated by the Timing Solenoid Valve (a clocked solenoid
valve).
With this solenoid valve permanently opened (pressure reduction), start of injection is
retarded. With it fully closed (pressure increase), start of injection is advanced. In the
intermediate range, the ON/OFF ratio (the ratio of solenoid valve open to solenoid valve
closed) can be infinitely varied by the ECM.
SENSORS
The position of the throttle and the control collar in the injection pump are registered by the
angle sensors. These use either contacting or non-contacting methods. Engine speed and
TDC are registered by inductive sensors. Sensors with high measuring accuracy and
long-term stability are used for pressure and temperature measurements. The start of
injection is registered by a sensor that is directly integrated in the nozzle holder and which
detects the start of injection by sensing the needle movement.
Page 5A-28
SERVICE MANUAL NUMBER 22
90-860074--1 FEBRUARY 2002