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 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 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 dedi-
cated 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.

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 PCM drives the idle air control (IAC) 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 A/C switch is turned off and on while the

engine is idling, the IAC motor adjusts the throttle

valve bypass 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 an abnormality is detected in one of the

sensors or actuators related to emission control,
the Malfunction Indicator Lamp (SERVICE
ENGINE SOON or Check Engine Lamp) illumi-
nates to warn the driver.

• When an abnormality is detected in one of the

sensors or actuators, a diagnostic trouble code
corresponding to the abnormality 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.

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.

Evaporative Emission Purge Control

• (Refer to GROUP 17, Emission Control System −

Evaporative Emission Control System

− General

Description

P.17-107

EGR Control

• (Refer to GROUP 17, Emission Control System −

Exhaust Gas Recirculation (EGR) System - Gen-
eral Description

P.17-111

GENERAL DESCRIPTION

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-3

MULTIPORT FUEL INJECTION (MFI) SYSTEM DIAGRAM

NOTE: For the vacuum routing, refer to GROUP 17,

Emission Control System

−

Vacuum Hoses

−

Vac-

uum Hose Routing

P.17-103

AK301864

1 LEFT BANK HEATED OXYGEN SENSOR (FRONT)
2 VOLUME AIRFLOW SENSOR
3 INTAKE AIR TEMPERATURE SENSOR
4 THROTTLE POSITION SENSOR
5 CAMSHAFT POSITION SENSOR
6 CRANKSHAFT POSITION SENSOR
7 BAROMETRIC PRESSURE SENSOR
8 ENGINE COOLANT TEMPERATURE SENSOR
9 LEFT BANK HEATED OXYGEN SENSOR (REAR)
10 RIGHT BANK HEATED OXYGEN SENSOR (FRONT)
11 RIGHT BANK HEATED OXYGEN SENSOR (REAR)
12 FUEL TANK DIFFERENTIAL PRESSURE SENSOR
13 MANIFOLD ABSOLUTE PRESSURE SENSOR
14 FUEL TANK TEMPERATURE SENSOR
15 FUEL LEVEL SENSOR

POWER SUPPLY
VEHICLE SPEED SENSOR
A/C SWITCH
TRANSMISSION RANGE SWITCH
POWER STEERING PRESSURE SWITCH
IGNITION SWITCH - ST
KNOCK SENSOR

1 INJECTOR
2 EVAPORATIVE EMISSION
PURGE SOLENOID
3 IDLE AIR CONTROL MOTOR
4 EVAPORATIVE EMISSION
VENTILATION SOLENOID
5 EGR VACUUM REGULATOR
SOLENOID VALVE

FUEL PUMP RELAY
MULTIPORT FUEL INJECTION
(MFI) RELAY
A/C COMPRESSER CLUTCH RELAY
SERVICE ENGINE SOON/
MALFUNCTION INDICATOR LAMP
DIAGNOSTIC OUTPUT
IGNITION COIL,
IGNITION POWER TRANSISTER

SENSE

DECIDE

ACT

PCM

4 THROTTLE POSITION SENSOR

3 IDLE AIR CONTROL MOTOR

1 INJECTOR

4 EVAPORATIVE EMISSION
VENTILATION SOLENOID

2 EVAPORATIVE EMISSION
PURGE SOLENOID

EVAPORATIVE
EMISSION
CANISTER

3 INTAKE AIR TEMPERATURE
SENSOR

5 CAMSHAFT POSITION
SENSOR

1 LEFT BANK HEATED
OXYGEN SENSOR (FRONT)

9 LEFT BANK HEATED
OXYGEN SENSOR (REAR)

CATALYTIC CONVERTER

13 MANIFOLD
ABSOLUTE
PRESSURE
SENSOR

ENGINE
COOLANT
TEMPERATURE
SENSOR

RIGHT BANK
HEATED
OXYGEN
SENSOR
(FRONT)

RIGHT BANK
HEATED OXYGEN
SENSOR (REAR)

FUEL
PRESSURE
REGULATOR

12 FUEL TANK DIFFERENTIAL
PRESSURE SENSOR

VOLUME AIRFLOW SENSOR
(WITH BAROMETRIC
PRESSURE SENSOR)

AIR INLET

FUEL TANK

EGR
VALVE

FROM
FUEL
PUMP

TO
FUEL
TANK

6 CRANKSHAFT POSITION
SENSOR

NOTE
* : Manifold port

14 FUEL TANK TEMPERATURE
SENSOR

15 FUEL LEVEL SENSOR

VENT
VALVE

5
EGR VACUUM
REGULATOR
SOLENOID
VALVE

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-4

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TROUBLESHOOTING STRATEGY

M1131150000546

NOTE: If a DTC is erased, its "freeze frame" data will
be also erased and the system readiness test status
will be reset. Store the "freeze frame" data before
erasing the DTC.
Use these steps to plan your diagnostic strategy. If
you follow them carefully, you will be sure to have
exhausted most of the possible ways to find an MFI
fault.
1. Gather as much information as possible about the

complaint from the customer.

2. Verify that the condition described by the

customer exists.

3. Check the vehicle for any MFI Diagnostic Trouble

Code (DTC).

4. If you cannot verify the condition and there are no

DTCs, the malfunction is intermittent. For
information on how to cope with intermittent
malfunctions, refer to GROUP 00, How to Use
Troubleshooting/Inspection Service Points

− How

to cope with Intermittent Malfunction

P.00-7

5. If you can verify the condition but there are no

DTCs, or the system cannot communicate with
the scan tool, refer to the trouble symptom
classification table.

6. If there is a DTC, record the number of the code,

then erase the code from the memory using the
scan tool.

7. Reconfirm the malfunction symptom and carry out

a test drive with the drive cycle pattern.

8. If DTC is set again, carry out an inspection with

the diagnostic trouble code procedures of that
code.

9. If DTC is not set again, the malfunction is

intermittent. For information on how to cope with
intermittent malfunctions, refer to GROUP 00,
How to Use Troubleshooting/Inspection Service
Points

− How to cope with Intermittent Malfunction

P.00-7

10.After repairs are completed, conduct a road test

duplicating the complaint set conditions to confirm
the malfunction has been connected.

NOTE: If the powertrain control module (PCM) is
replaced, Immobilizer Encrypted Code Registration
should be carried out, Refer to GROUP 54A, Ignition
Switch

−

On-vehicle Service

−

Immobilizer Encrypted

Code Registration

P.54-65

DIAGNOSTIC FUNCTION

M1131155500193

MALFUNCTION INDICATOR LAMP (SERVICE ENGINE
SOON OR CHECK ENGINE LAMP)
Among the on-board diagnostic items, a Malfunction Indicator
Lamp (SERVICE ENGINE SOON or Check Engine Lamp) illu-
minates to notify the driver of an emission control malfunction.
However, when an irregular signal returns to normal and the
powertrain control module (PCM) judges that it has returned to
normal, the Malfunction Indicator Lamp (SERVICE ENGINE
SOON or Check Engine Lamp) is switched off.
Moreover, when the ignition switch is turned off, the lamp is
switched off. Immediately after the ignition switch is turned on,
the Malfunction Indicator Lamp (SERVICE ENGINE SOON or
Check Engine Lamp) is lit for five seconds to indicate that the
Malfunction Indicator Lamp (SERVICE ENGINE SOON or
Check Engine Lamp) operates normally.

SERVICE

ENGINE

SOON

BRAKE

A/T

TEMP

HOLD

ANTI

LOCK

CRUISE

AK000325AC

MALFUNCTION INDICATOR LAMP
(SERVICE ENGINE SOON OR
CHECK ENGINE LAMP)

Content .. 145 146 147 148 ..