GENERAL INFORMATION
TSB Revision
MULTIPORT FUEL INJECTION (MFI) <3.0L>
13B-3
GENERAL INFORMATION
M1131000100961
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The Multiport Fuel Injection System consists of sen-
sors which detect the engine conditions, the ENGINE
CONTROL MODULE (ECM) <M/T>/POWERTRAIN
CONTROL MODULE (PCM) <A/T> which controls
the system based on signals from these sensors,
and actuators which operate under the control of the
ECM <M/T>/PCM <A/T>. The ECM <M/T>/PCM
<A/T> carries out activities such as fuel injection con-
trol, idle air control, and ignition timing control. In
addition, the ECM <M/T>/PCM <A/T> is equipped
with several diagnostic test modes which simplify
troubleshooting when a problem develops.
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FUEL INJECTION CONTROL
The injection 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 crank-
shaft. The firing order is 1-2-3-4-5-6. Each cylinder
has a dedicated fuel injector. This is called multiport.
The ECM <M/T>/PCM <A/T> provides a richer
air/fuel mixture by carrying 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 operat-
ing temperature after warming-up, the ECM
<M/T>/PCM <A/T> 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.
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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 ECM <M/T>/PCM
<A/T> 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 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 IAC motor adjusts the throttle valve bypass
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 condi-
tions. The ignition timing is determined by the ECM
<M/T>/PCM <A/T> from engine speed, intake air vol-
ume, engine coolant temperature, and atmospheric
pressure.
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DIAGNOSTIC TEST MODE
• When an abnormality is detected in one of the
sensors or actuators related to emission control,
the MALFUNCTION INDICATOR LAMP (SER-
VICE ENGINE SOON OR CHECK ENGINE
LAMP) illuminates 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
ECM <M/T>/PCM <A/T>.
• The RAM data inside the ECM <M/T>/PCM
<A/T> that is related to the sensors and actuators
can be read with the scan tool. In addition, the
actuators can be controlled by MB991958
(MUT-III Sub Assembly) under certain circum-
stances.
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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.
• 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.
• Intake Manifold Tuning