The Multiport Fuel Injection System consists of sen-
sors, actuators and the powertrain control module
(PCM). The sensors detect the engine condition. The
PCM controls the system based on signals from
these sensors. The actuators work under the control
of the PCM. The PCM carries out activities such as
fuel injection control, throttle valve opening control,
idle air control, and ignition timing control. In addition,
the PCM has several diagnostic test modes which
simplify troubleshooting when a problem develops.

FUEL INJECTION CONTROL
The PCM controls injector drive times and injection
timing to supply the optimum air/fuel mixture to the
engine according to the continually-changing engine
operation conditions. A single injector is mounted at
the intake port of each cylinder. The fuel pump sup-
plies pressurized fuel from the fuel tank to the fuel
injectors. The fuel pressure regulator controls the
fuel pressure. Thus, the regulated fuel is distributed
to each injector. Fuel is normally injected for each
cylinder every two rotations of the crankshaft. The fir-
ing order is 1-3-4-2. Each cylinder has a dedicated
fuel injector. This is called "multiport". The PCM pro-
vides a richer air/fuel mixture by carrying out
"open-loop" control when the engine is cold or run-
ning under high load conditions. Thus, engine perfor-
mance is maintained. In addition, when the engine is
under normal operating temperature after warm-
ing-up, the PCM controls the air/fuel mixture accord-
ing to the heated oxygen sensor signal. This control
is a "closed-loop" control. The closed-loop control
achieves the theoretical air/fuel mixture ratio where
the catalytic converter can obtain 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 primary cur-
rent flow to the ignition coil. This maintains ignition
timing at an optimum level regardless of various
engine operating conditions. The PCM determines
the ignition timing according to engine speed, intake
air volume, engine coolant temperature, and atmo-
spheric pressure.

DIAGNOSTIC TEST MODE

• When a fault is detected in any 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 the scan tool MB991958 (MUT-III sub
assembly) under certain circumstances.

GENERAL DESCRIPTION

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MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-3

OTHER CONTROL FUNCTIONS

Fuel Pump Control

• Turns on the fuel pump relay so that current is

supplied to the fuel pump while the engine is
cranking or running.

A/C Compressor Clutch Relay Control

• Turns on and off the air conditioning compressor

clutch.

Engine Oil Control Valve Control

• The PCM effects duty cycle control on the engine

oil control valve, in accordance with the engine
speed. This regulates the supply of engine oil to
the intake rocker shaft, which switches the cams.

Fan Relay Control

• The radiator fan and condenser fan speeds are

controlled in response to the engine coolant tem-
perature and vehicle speed.

Generator Output Current Control

• Prevents generator output current from increas-

ing suddenly and idle speed from dropping at
times such as when the headlights are turned on.

Evaporative Emission Purge Control

• (Refer to GROUP 17, Emission Control System −

Evaporative Emission System

− General Informa-

tion.

P.17-85

)

EGR Control

• (Refer to GROUP 17, Emission Control System −

Exhaust Gas Recirculation (EGR) System

− Gen-

eral Information.

P.17-91

)

GENERAL DESCRIPTION

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MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-4

MULTIPORT FUEL INJECTION (MFI) SYSTEM DIAGRAM

NOTE: For the vacuum hose routing, refer to
GROUP 17, Vacuum Hoses

P.17-79

AK302201

1 MASS AIRFLOW SENSOR
2 INTAKE AIR TEMPERATURE SENSOR
3 THROTTLE POSITION SENSOR (MAIN/SUB)
4 MANIFOLD ABSOLUTE PRESSURE SENSOR
5 CAMSHAFT POSITION SENSOR
6 ENGINE COOLANT TEMPERATURE SENSOR
7 KNOCK SENSOR
8 CRANKSHAFT POSITION SENSOR
9 CYLINDER 1, 4 HEATED OXYGEN SENSOR
(FRONT)
10 CYLINDER 2, 3 HEATED OXYGEN SENSOR
(FRONT)
11 CYLINDER 1, 4 HEATED OXYGEN SENSOR
(REAR)
12 CYLINDER 2,3 HEATED OXYGEN SENSOR
(REAR)
13 FUEL TANK DIFFERENTIAL PRESSURE SENSOR
14 FUEL TANK TEMPERATURE SENSOR
15 FUEL LEVEL SENSOR

ACCELERATOR PEDAL POSITION SENSOR
(MAIN/SUB)
POWER STEERING PRESSURE SWITCH
ENGINE OIL PRESSURE SWITCH
OUTPUT SHAFT SPEED SENSOR
TRANSMISSION RANGE SWITCH
GENERATOR FR TERMINAL
IGNITION SWITCH - IG
IGNITION SWITCH - ST
POWER SUPPLY

1 THROTTLE ACTUATOR
CONTROL MOTOR
2 INJECTOR
3 ENGINE OIL CONTROL VALVE
4 EGR VALVE
(STEPPER MOTOR)
5 EVAPORATIVE EMISSION
PURGE SOLENOID
6 EVAPORATIVE EMISSION
VENTILATION SOLENOID

IGNITION COIL, IGNITION
POWER TRANSISTER
MULTIPORT FUEL
INJECTION (MFI) RELAY
FUEL PUMP RELAY
THROTTLE ACTUATOR
CONTROL MOTOR RELAY
GENARATOR G TERMINAL
HEATED OXYGEN SENSOR
HEATER
FAN CONTROL RELAY
(RADIATOR, A/C CONDENSER)
A/C COMPRESSOR CLUTCH
RELAY
DIAGNOSTIC OUTPUT

PCM (WITH
BAROMETRIC
PRESSURE
SENSOR)

SENSE

DECIDE

ACT

1 MASS AIRFLOW

SENSOR

AIR
INLET

2 INTAKE AIR TEMPERATURE

SENSOR

THROTTLE
ACTUATOR
CONTROL
MOTOR

3 THROTTLE POSITION SENSOR
(MAIN/SUB)

MANIFOLD
ABSOLUTE
PRESSURE
SENSOR

ENGINE
COOLANT
TEMPERATURE SENSOR

2 INJECTOR

8 CRANKSHAFT POSITION

SENSOR

CYLINDER 2, 3
HEATED OXYGEN
SENSOR (FRONT)

5 CAMSHAFT

POSITION
SENSOR

4 EGR VALVE

(STEPPER MOTOR)

5 EVAPORATIVE

EMISSION
PURGE SOLENOID

6 EVAPORATIVE

EMISSION
VENTILATION
SOLENOID

EVAPORATIVE EMISSION
VENTILATION VALVE

13 FUEL TANK

DIFFERENTIAL
PRESSURE
SENSOR

14 FUEL TANK

TEMPERATURE
SENSOR

FUEL TANK

EVAPORATIVE
EMISSION
CANISTER

FUEL PUMP

15 FUEL

LEVEL
SENSOR

3 ENGINE OIL

CONTROL
VALVE

KNOCK
SENSOR

FUEL PRESSURE
REGULATOR

9 CYLINDER 1, 4

HEATED OXYGEN
SENSOR (FRONT)

CYLINDER 1, 4
HEATED OXYGEN
SENSOR (REAR)

CYLINDER 2, 3
HEATED OXYGEN
SENSOR (REAR)

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