The unit injector fuel injection system consists of sensors which detect the condition
of the diesel engine, an engine electronic control unit (engine-ECU) which controls the system
based on signals from these sensors, and actuators which operate according to control commands
from the engine-ECU. The engine-ECU carries out activities such as fuel injection control and
idle speed control. In addition, the engine-ECU is equipped with several self-diagnosis functions
which make troubleshooting easier in the event that a problem develops.
FUEL INJECTION CONTROL
The injector drive time, the injection timing and the fuel pressure are controlled so
that the appropriate quantities of fuel are supplied to the engine in response to engine conditions
which can change frequently. A single injector is mounted at each cylinder. The fuel is sent
from the fuel tank by the electrical fuel pump to the unit injector through the tandem pump.
The unit injector pump increases the fuel pressure to the pressure which is required for high-pressure
injection.
IDLE SPEED CONTROL
The idle speed is kept at the optimum speed by controlling the fuel injection quantity
in accordance with changes in idling conditions and engine load during idling. The engine-ECU drives the fuel injector to keep the engine running at the pre-set idle
target speed in accordance with the engine coolant temperature and A/C and other electrical
load.
SELF-DIAGNOSIS FUNCTION
When an abnormality is detected in any of the sensors or actuators, the engine
warning lamp illuminates to warn the driver.
When an abnormality is detected in any of the sensors or actuators, a diagnosis
code number corresponding to the problem which occurred is output.
The RAM data relating to the sensors and actuators which is stored in the engine-ECU
can be read using the M.U.T.-III. In addition, the actuator can be force-driven under certain conditions.
OTHER CONTROL FUNCTIONS
Fuel Pump Control Turns the fuel pump relay ON so that current is supplied to the fuel pump while the engine
is cranking or running.
Glow Control The engine-ECU sends the information for the glow function to the automatic glow period
control unit.
EGR Control The engine-ECU controls the EGR control solenoid valve, intake air control flap, and EGR cooler
solenoid valve to supply optimum EGR amount according to the drive conditions.
Boost Pressure Control The variable geometry solenoid valve is duty controlled by the engine-ECU to control the variable
nozzle-opening angle of the variable geometry turbocharger. This allows obtaining the characteristic
of boost pressure corresponding to the engine operation condition.
A/C Compressor Control Actuated the A/C compressor in accordance with the signals provided by the A/C-ECU via Controller
Area Network (CAN) communication.
Alternator Control The engine-ECU supplies the excitation current to the alternator and monitors the alternator
load. The engine-ECU requests the charging warning lamp to go ON/OFF based on the alternator
load and the battery voltage.
Starter Relay Control When an ignition switch-ST signal is input from the ignition switch, the engine-ECU turns
ON the power transistor for controlling the starter relay. As a result, current flows through
the coil of the starter relay, turns ON the relay switch, and actuates the starter motor.
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