GENERAL INFORMATION
MULTIPOINT FUEL INJECTION (MPI)
13A-5
GENERAL INFORMATION
M1131000106680
The Multipoint Fuel Injection System consists of sen-
sors which detect the engine conditions, the
engine-ECU which controls the system based on sig-
nals from these sensors, and actuators which oper-
ate under the control of the engine-ECU. The
engine-ECU carries out activities such as fuel injec-
tion control, idle speed control and ignition timing
control. In addition, the engine-ECU is equipped with
several diagnosis modes which simplify trouble-
shooting 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.
THROTTLE VALVE OPENING CONTROL
This system electronically 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 valve control servo, which is mounted on
the throttle body, in order to attain the target throttle
valve opening that has been predetermined in
accordance with driving conditions.
IDLE SPEED 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 valve control
servo 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 A/C switch is turned off and on
while the engine is idling, the throttle valve control
servo adjusts the throttle valve passes through air
amount according to the engine load conditions 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 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.