DESCRIPTION
SERVICE MANUAL NUMBER 22
90-860074--1 FEBRUARY 2002
Page 5A-27
Modes Of Operation
PREHEATING THE GLOW PLUGS (IF EQUIPPED)
The operation of the glow plugs and the glow plug preheating on-time is controlled by the
ECM. The time period during which the glow plugs are ON (supplied 12 volts) depends
directly on the temperature of the engine coolant (coolant temperature sensor) and the
altitude of the engine. The altitude is determined by the BARO Barometric Absolute
pressure sensor located inside the ECM. The ignition OFF time in which the engine can be
restarted without the preheat cycle is about 20 seconds.
The ECM also uses a post heat strategy, in which power to the glow plugs (12 v) is
maintained after engine start-up. This time period is calculated by the ECM and is based
on engine ECT sensor signal equivalent to approximately 60
°
C (140
°
F) and engine speed
up to 1500 rpm. By using coolant temperature and engine rpm references it is possible to
reduce cold engine noise as well as emissions after starting.
ENGINE STARTING
During engine starting the ECM does not look at the throttle position information. The throttle
position has no influence on the starting procedure. Additionally, the ECM ignores the input
signal from the instrumented first injector. While starting, the fuel flow rate is determined
exclusively on the basis of the engine speed and the engine coolant temperature input
information. The ECM sets the fuel injection timing based on the signal from the coolant
temperature sensor.
ENGINE OPERATION
During engine operation, the ECM calculates the fuel flow rate based on signals from the
throttle position sensor and Engine rpm Speed sensor. This information is then sent to the
injection pump, which regulates the rate of the fuel flowing into the cylinders of the engines.
The injection pump uses a rotating electromagnetic actuator to move the delivery plunger
which controls the pumps working stroke and the amount of fuel flow. The quantity of fuel
to be injected is also corrected based on the following parameters:
•
Fuel temperature. The ECM uses this information to calculate the exact weight of the
fuel injected. The pump actually controls the volume of fuel, but the calculation of the
air/fuel ratio by the ECM requires knowledge of the weight of the fuel injected. The
weight of the fuel is determined by fuel temperature.
•
Air intake temperature and absolute barometric pressure. These inputs are needed
by the ECM to optimize the ideal air/fuel ratio for the prevailing engine operating
conditions.
The maximum flow rate of the fuel entering the engine is limited according to the torque
curve based on the engine speed. The actual position of the fuel quantity actuator, which
is necessary to send the correct amount of fuel to the injectors, is detected by the Fuel
Quantity Sensor (an inductive control-collar position sensor or potentiometer) located on
the actuator. By comparing the real data and the calculated data, the ECM constantly
changes the position of the actuator.
