Multipoint Fuel; General; Outline Of Change - Mitsubishi MOTORS Space Runner 1999 Workshop Manual Supplement

13D-2
MULTIPOINT FUEL INJECTION (MPI)

GENERAL

OUTLINE OF CHANGE

The following service procedures have been established in line with the addition of SPACE RUNNER
vehicles with 4G63-MPI engine.
GENERAL INFORMATION
The Multipoint Fuel Injection System consists
of sensors which detect the engine conditions,
the engine-ECU which controls the system
based on signals from these sensors, and
actuators which operate under the control of
the engine-ECU. The engine-ECU carries out
FUEL INJECTION CONTROL
The injector drive times and injector timing are
controlled so that the optimum air/fuel mixture
is supplied to the engine to correspond to the
continually-changing engine operation condi-
tions.
A single injector is mounted at the intake port
of each cylinder. Fuel is sent under pressure
from the fuel tank by the fuel pump, with the
pressure being regulated by the fuel pressure
regulator. The fuel thus regulated is distributed
to each of the injectors.
Fuel injection is normally carried out once for
each cylinder for every two rotations of the
crankshaft. The firing order is 1-3-4-2. This is
called sequential fuel injection.
IDLE AIR CONTROL
The idle speed is kept at the optimum speed
by controlling the amount of air that bypasses
the throttle valve in accordance with changes
in idling conditions and engine load during
idling. The engine-ECU drives the idle speed
control (ISC) motor to keep the engine running
at the pre-set idle target speed in accordance
with the engine coolant temperature and air
IGNITION TIMING CONTROL
The power transistor located in the ignition
primary circuit turns ON and OFF to control
the primary current flow to the ignition coil. This
controls the ignition timing in order to provide
the optimum ignition timing with respect to the
MPI -
General/General Information
activities such as fuel injection control, idle
speed control and ignition timing control. In
addition, the engine-ECU is equipped with
several diagnosis modes
troubleshooting when a problem develops.
The engine-ECU provides a richer air/fuel
mixture by carrying out "open-loop" control
when the engine is cold or operating under
high load conditions in order to maintain engine
performance. In addition, when the engine is
warm or operating under normal conditions,
the engine-ECU controls the air/fuel mixture
by using the oxygen sensor signal to carry out
"closed-loop" control in order to obtain the
theoretical air/fuel mixture ratio that provides
the maximum cleaning performance from the
three way catalyst.
conditioner load. In addition, when the air
conditioner switch is turned off and on while
the engine is idling, the ISC motor operates
to adjust the throttle valve bypass air amount
in accordance with the engine load conditions
in order to avoid fluctuations in the engine
speed.
engine operating conditions. The ignition timing
is determined by the engine-ECU from the
engine speed, intake air volume, engine coolant
temperature and atmospheric pressure.
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