The Multipoint Fuel Injection System consists of sen-
sors 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 air control, and ignition timing
control.
In addition, the ENGINE-ECU is equipped with a
number of diagnostic test modes which simplify trou-
bleshooting when a problem develops.

FUEL INJECTION CONTROL

The injector drive times and injector timing are con-
trolled so that the optimum air/fuel mixture is sup-
plied to the engine to correspond to the
continually-changing engine operation conditions.
A single injector is mounted at the intake port of each
cylinder. Fuel is sent under pressure from the fuel
tank to the fuel injectors by the fuel pump, with the
pressure being regulated by the fuel pressure regula-
tor. The regulated fuel 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 1-2-3-4-5-6. Each cylinder has a
dedicated fuel injector. This is called multiport.
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 under normal operating tempera-
ture after warming-up, the ENGINE-ECU controls the
air/fuel mixture by using the heated oxygen sensor
signal to carry out "closed-loop" control. The
closed-loop control achieves the theoretical air/fuel
mixture ratio where the catalytic converter can
obtains the maximum cleaning performance.

THROTTLE VALVE OPENING CONTROL

This system electrically controls the opening of the
throttle valve. The ENGINE-ECU detects the amount
of travel of the accelerator pedal via the accelerator
pedal position sensor, and controls the actuation of
the throttle actuator control motor, which is mounted
on the throttle body, in order to attain the target throt-
tle valve opening that has been predetermined in
accordance with driving conditions.

IDLE AIR CONTROL

The idle speed is kept at the optimum speed by con-
trolling the amount of air that passes through the
throttle valve in accordance with changes in idling
conditions and engine load during idling.
The ENGINE-ECU drives the throttle actuator control
motor 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. In
addition, when the air conditioning switch is turned
off and on while the engine is idling, the throttle actu-
ator control motor adjusts the throttle valve passes
through air amount according to the engine load con-
ditions to avoid fluctuations in the engine speed.

IGNITION TIMING CONTROL

The ignition power transistor located in the ignition
primary circuit turns ON and OFF to control the pri-
mary current flow to the ignition coil. This controls the
ignition timing to provide the optimum ignition timing
with respect to the engine operating conditions. The
ignition timing is determined by the ENGINE-ECU
from engine speed, intake air volume, intake air tem-
perature and engine coolant temperature.

DIAGNOSTIC TEST MODE

• When a fault is detected in one of the sensors or

actuators related to emission control or major
engine control system, the (Check Engine Warn-
ing Lamp) illuminates to warn the driver.

• When a fault is detected in one of the sensors or

actuators, a diagnostic trouble code correspond-
ing to the fault is stored in the ENGINE-ECU.

• The RAM data inside the ENGINE-ECU that is

related to the sensors and actuators can be read
with the diagnostic tool. In addition, the actuators
can be controlled by diagnostic tool (MUT-III sub
assembly) under certain circumstances.

GENERAL DESCRIPTION

MULTIPOINT FUEL INJECTION (MPI)

13A-3

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.

A/C Compressor Clutch Relay Control

• Turns the compressor clutch of the A/C ON and

OFF.

Fan Control (PWM)

• The radiator fan and condenser fan speeds are

controlled by the Fan Controller unit (PWM) in
response to the engine coolant temperature and
vehicle speed via the engine ECU.

Evaporative Emission Purge Control

• (Refer to GROUP 17, Emission Control System −

Evaporative Emission System

− General Descrip-

tion

P.17-81

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