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 con-
trol, 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 injection 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 by the fuel pump, with the pressure being regu-
lated 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 condi-
tions 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 con-
trolling 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 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 condi-
tioner switch is turned off and on while the engine is
idling, the idle speed control motor operates to adjust
the throttle valve bypass air amount in accordance
with the engine load conditions in order to avoid fluc-
tuations in the engine speed.

IGNITION TIMING CONTROL
The power transistor located in the ignition primary
circuit turns ON and OFF to control the primary cur-
rent 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

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.

When an abnormality is detected in one of the
sensors or actuators, a diagnosis code corre-
sponding to the abnormality is output.

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.

OTHER CONTROL FUNCTIONS

1. Fuel Pump Control

Turns the fuel pump relay ON so that current is sup-

plied to the fuel pump while the engine is crank-
ing or running.

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