The Multiport Fuel Injection System consists of sen-
sors which detect the engine conditions, the POW-
ERTRAIN CONTROL MODULE (PCM) which
controls the system based on signals from these
sensors, and actuators which operate under the con-
trol of the PCM.
The PCM carries out activities such as fuel injection
control, idle air control, and ignition timing control.
In addition, the PCM is equipped with several diag-
nostic test modes which simplify troubleshooting
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 PCM provides a richer air/fuel mixture by carry-
ing 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 temperature after
warming-up, the PCM 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 PCM 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 throttle
valve opening that has been predetermined in accor-
dance 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 PCM drives the throttle actuator control motor to
keep the engine running at the pre-set idle target
speed in accordance with the engine coolant temper-
ature 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 actuator control
motor 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 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 PCM from engine
speed, intake air volume, engine coolant tempera-
ture, and atmospheric pressure.

DIAGNOSTIC TEST MODE

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

actuators related to emission control, the Mal-
function Indicator Lamp (SERVICE ENGINE
SOON or Check Engine 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 PCM.

• The RAM data inside the PCM that is related to

the sensors and actuators can be read with the
scan tool. In addition, the actuators can be con-
trolled by scan tool MB991958 (MUT-III sub
assembly) under certain circumstances.

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