GENERAL INFORMATION
TSB Revision
MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>
13A-3
GENERAL INFORMATION
M1131000105999
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The Multiport Fuel Injection System consists of sen-
sors which detect the engine conditions, the ENGINE
CONTROL MODULE (ECM) which controls the sys-
tem based on signals from these sensors, and actua-
tors which operate under the control of the ECM.
The ECM carries out activities such as fuel injection
control, idle air control, and ignition timing control.
In addition, the ECM is equipped with several diag-
nostic test modes which simplify troubleshooting
when a problem develops.
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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 1-3-4-2. Each cylinder has a dedi-
cated fuel injector. This is called multiport.
The ECM 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 ECM controls the air/fuel mixture by
using the heated oxygen sensor signal or linear
air-fuel ratio sensor signal to carry out "closed-loop"
control. The closed-loop control achieves the theo-
retical air/fuel mixture ratio where the catalytic con-
verter can obtain the maximum cleaning
performance.
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THROTTLE VALVE OPENING CONTROL
This system electrically controls the opening of the
throttle valve. The ECM 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.
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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 ECM 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 pass-through air
amount according to the engine load conditions to
avoid fluctuations in the engine speed.
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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 ECM from engine
speed, intake air volume, engine coolant tempera-
ture, and atmospheric pressure.
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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 ECM.
• The RAM data inside the ECM 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 (M.U.T.-III sub
assembly) under certain circumstances.
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