MPI <4G9> –
General Information
13C-2
GENERAL
OUTLINE OF CHANGES
The following contents have been established to correspond to the addition of vehicles with 4G9-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
activities such as fuel injection control, idle
speed control and ignition timing control. In
addition, the engine-ECU is equipped with
several diagnosis modes which simplify
troubleshooting when a problem develops.
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. 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.
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
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.
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
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.
SELF-DIAGNOSIS FUNCTION
D
When an abnormality is detected in one
of the sensors or actuators related to
emission control, the engine warning lamp
(check engine lamp) illuminates as a
warning to the driver.
D
When an abnormality is detected in one
of the sensors or actuators, a diagnosis
code corresponding to the abnormality is
output.
D
The RAM data inside the engine-ECU that
is related to the sensors and actuators can
be read by means of the MUT-
II
. In addition,
the actuators can be force-driven under
certain circumstances.