M-STEP Ver.3
STEP-II
MPI System
TEXT BOOK
<MPI System>
CONTENTS
<MPI System>
1. OUTLINE OF MPI SYSTEM ------------------------------------ 1-1 / 1-9
(1) Air Fuel Mixture
(2) System Construction Overview
(3) System Components Overview
(4) Knowledge Check
2. SYSTEM COMPONENTS --------------------------------------- 2-1 / 2-20
(1) System Configuration
(2) Location of Components
(3) Engine-ECU
(4) Sensor
(5) Actuator
(6) Knowledge Check
3. MPI SYSTEM ------------------------------------------------------- 3-1 / 3-47
(1) Fuel Injection Control
(2) Ignition Control
(3) Throttle Valve Opening Angle Control and Idle Speed Control
(4) MIVEC
(5) Relay Controls
(6) Emission Control
(7) Immobilizer Function
(8) Diagnosis System
(9) Knowledge Check
4. CONTROLLER AREA NETWORK (CAN) ------------------ 4-1 / 4-3
(1) Configuration
(2) Voltage Transformation
(3) Knowledge Check
5. ON-VEHICLE INPECTION AND SERVICE ----------------- 5-1 / 5-21
(1) Electrical Wiring Diagram
(2) Required Service procedure When Engine-ECU Replaced
(3) Initialization Procedure for Learning Value in MPI Engine
(4) Initialization Procedure for Throttle Valve Servo
(5) How to Reduce Pressurized Fuel pressure
(6) Check the Injector Spray Condition
(7) Fuel Pressure Test
(8) Data List Reference Table
(9) Actuator Test Reference Table
1. OUTLINE OF MPI SYSTEM
1. AIR-FUEL MIXTURE
(1) Air-fuel Ratio
A gasoline engine generates power output by the
combustion when an air-fuel mixture enters the
cylinders. The air-fuel mixture is expressed as a
weight ratio known as stoichiometric, and it is
14.7 kg
said to be balanced when there is a mix of 14.7
parts of air to 1 part of fuel as shown in the Fig. 1
1 kg
-1. Theoretically speaking, this means that a
complete combustion can be achieved when the
air to fuel ratio is 14.7:1.
When the air-fuel ratio is smaller than stoichio-
Fig. 1-1 metric, like 11:1, less air enters the cylinder, and
the mixture is called a rich mixture. On the con-
trary when the ratio is larger than one, like 16:1,
more air enters the cylinder and the mixture is
called a lean mixture.
Fig. 1-2
As shown in Fig. 1-2 the suitable air-fuel ratio varies depending on the engine and driv-
ing conditions. For example, when starting a cold engine, a rich mixture is required. And
when driving at a constant cruising speed after the engine has warmed-up, a lean mix-
ture is required for the engine to generate enough power output.
1 - 1 MMMTC VER 1
1. OUTLINE OF MPI SYSTEM
(2) How the Air-Fuel Mixture is Made
On an electronic controlled fuel injection system, the electro-magnetic type injectors are
installed in the intake manifold. Pressurized fuel is applied to the injectors, and the fuel is
injected into the intake manifold through the nozzle of the injector when the Engine-ECU
makes the ground connection to the respective injector. As intake air, which is regulated
by the throttle valve, flows in into each cylinder, it mixes with the injected fuel to create
the Air-Fuel Mixture.
Drive signal from Engine-ECU
Injector
Fig. 1-3
MMMTC VER 1 1 - 2
1. OUTLINE OF MPI SYSTEM
2. SYSTEM CONSTRUCTION OVERVIEW
Electronically controlled gasoline injection systems used in Mitsubishi Motors vehicles con-
sist of a fuel supply system, ignition system, air control system, and emission control sys-
tem. The 4B1 MPI system configuration as a typical example is shown in Fig. 1-4.
Fig. 1-4
Mitsubishi’s multi-point fuel injection (MPI) system is classified into two types according to
the air flow sensor that detects the intake air volume as shown in Fig 1-5. One is called
mass flow type sensor which detects air flow by applying a Kármán Vortex principle. This
type of sensor is capable of providing a digital representation of the air flow rate to enable
the fuel injection system to operate accurately and responsively. The other type of MPI sys-
tem (used in 4A9-series engines) is called speed-density type, and it employs a speed-
density arrangement that uses an intake manifold pressure sensor to produce the elec-
tronic representation of air-flow-rate.
Air flow sensor
Manifold absolute
pressure sensor
Engine-ECU Engine-ECU
Fig. 1-5
1 - 3 MMMTC VER 1
1. OUTLINE OF MPI SYSTEM
(1) Fuel Supply System
The fuel supply system is comprised of electro-
magnetic type injectors, a delivery pipe, a motor-
driven fuel pump that feeds fuel under pressure,
and Engine-ECU which activates and controls the
injectors and the fuel pump based on output signals
supplied by various sensors. A fuel filter and a
pressure regulator are incorporated into the fuel
tank pump and gauge assembly. A return-less fuel
Fig. 1-6 system eliminates fuel being returned from the en-
gine compartment to reduce fuel tank temperature
and the production of evaporative emissions.
Fig. 1-7
<Fuel tank pump and gauge assembly>
The fuel tank pump and gauge assembly consists of the following components:
◇ Fuel pump assembly (fuel pump and fuel pressure regulator)
◇ Fuel tank gauge unit
◇ Fuel filter
Fuel flange and filter assembly
Fuel gauge unit
Fuel pump pressure regulator
Fuel pump assembly
Fuel filter
Fig. 1-8
MMMTC VER 1 1 - 4
1. OUTLINE OF MPI SYSTEM
<Fuel passage>
The fuel pump displaces the fuel through the fuel filter and then through the main fuel
pipe before it is delivered to the injectors through the delivery pipe. A fuel pressure regu-
lator is part of the fuel tank pump and gauge assembly to maintain a fuel pressure of
324kPa. When the Engine-ECU connects the injector, electrical current flows through
the injector coil, and the injector nozzle opens to spray fuel into the intake manifold.
F/Press
Regula-
Fig. 1-9
<Fuel pump>
The fuel pump is called the in-tank type. The ad-
vantages of this setup are that the pump is
mounted in the fuel tank and immersed in the
fuel to reduce the operating sound and the possi-
bility of vapor lock. The fuel pump is also re-
ferred to as a wet type because it is filled with
fuel in its inside. The pump consists of a ferrite
DC motor which drives an impeller pump inside a
pump casing. These are assembled together as
a single unit. In addition, a relief valve and a
check valve are included as part of the assem-
bly.
Fig. 1-10
◇ Fuel pressure feed function
When the motor drives the impeller, a pressure difference is created between the areas
above and below the grooves provided on the impeller. As a result, the pump produces a
vortex type fuel displacement, and the fuel pressure becomes high. The fuel is then
forced out from the pump chamber and passes through the motor section. It then forces
the check valve to open, and the fuel is delivered through the discharge port.
◇ Relief valve
If the fuel discharge side gets blocked, the pressure in the fuel pump becomes abnor-
mally high. When the fuel pressure reaches 45 to 60 kPa, the relief valve opens up to let
the excess pressure escape back to the fuel tank, thereby preventing the fuel pressure
in the fuel line from rising above the specified pressure and damaging the pump.
◇ Check valve
When the engine is shut down, the fuel pump stops, and the spring loaded check valve
closes to retain a high pressure in the fuel lines. This way it facilitates restarting the en-
gine, and also prevents vapor locks at high ambient temperatures.
1 - 5 MMMTC VER 1
1. OUTLINE OF MPI SYSTEM
- For Your Reference -
Fig. 1-11 shows the Wesco type fuel pump used in
Mitsubishi vehicles. The impeller of the pump pro-
duces a pressure difference between the suction
and discharge vane grooves when the DC motors
drives the pump. The features of this pump type
are:
◆ Low noise & vibration, because the impeller
Fig. 1-11 and casing are not in contact with each other.
◆ Small discharge pulsations, thanks to a lack of
change in compression volume, which elimi-
nates the need for a pressure pulsation damp-
er, allowing for size and weight reduction.
(2) Ignition System
To support efficient combustion, the ignition system must ignite the air-fuel mixture at just
the right moment. Because fuel burns at a constant speed, correct ignition timing ensures
that the heat and the pressure resulting from combustion are released at the right time rela-
tive to the position of the piston. The Engine-ECU receives the output signals from related
sensors to control ignition timing.
Fig. 1-12
MMMTC VER 1 1 - 6
1. OUTLINE OF MPI SYSTEM
(3) Air Control System
The Engine-ECU also operates and controls the throttle valve in the whole range of the en-
gine operation, by means of a control servo located in the throttle body. When the Engine-
ECU detects the amount of accelerator pedal depression (as per operator’s intention)
through the accelerator pedal position sensor, the ECU pulses the servo control to realize
pre-set basic target opening angles, and adds various compensations and controls to the
actual throttle valve opening according to the target opening angle.
Fig. 1-13
(4) Emission Control System
The emission control system is required to control harmful emission elements like Hydro-
carbons (HC), Carbon Monoxide (CO), and Nitrogen Oxides (NOx). The following con-
trols are used to regulate these emissions on MMC vehicles.
Fig. 1-14
<Crankcase Emission Control>
Blow-by gas is the amount of air-fuel mix that leaks through the piston rings into the crank-
case when the piston is in the compression cycle. The Positive Crankcase Ventilation (PCV)
valve is provided to return the blow-by gas to back to the intake manifold.
<Evaporative Emission Control>
This control stores fuel vapors from the fuel tank into a canister. The stored vapors are then
mixed with intake air and burned in the combustion chamber.
<Air/ Fuel ratio control for catalytic converter>
The catalytic converter can purify the above three harmful elements contained in the ex-
haust emission by a chemical reaction effectively under the stoichiometric A/F ratio condi-
tion.
1 - 7 MMMTC VER 1
1. OUTLINE OF MPI SYSTEM
3. SYSTEM COMPONENTS OVERVIEW
The Engine-ECU is the central control of the MPI System. The Engine-ECU uses the output
information from various sensors to calculate the optimum fuel injection timing and quantity,
the proper ignition timing, and the idling speed correction coefficient. It also issues drive sig-
nals to the relevant actuators in accordance with the results of its calculations.
(1) Sensors
Sensors are devices that the Engine-ECU uses to
measure and monitor the operational conditions
that determine the requirements for fuel supply,
ignition timing, idle air flow, etc. Some of these con-
ditions are engine coolant temperature, vehicle alti-
tude, and air temperature / volume flowing through
the intake manifold.
Fig. 1-15
(2) Engine-ECU
The Engine-ECU is a device that monitors operating conditions, and uses an internal pro-
gram to calculate fuel supply, ignition timing, and other controls.
After making the calculations, the Engine-ECU makes corresponding connections to the
actuators components to supply the correct amount of fuel, and to ignite the air-fuel mixture
at the correct time, for the operating conditions that are present.
As conditions change, the Engine-ECU continues to update its calculations and adjust fuel
supply, ignition timing, and make other control decisions as needed. This process continues
as long as the vehicle is running.
Computer controlled engines has the advantage to respond quickly to changes in operating
conditions, especially when a driver has a demand for power. The Engine-ECU can also
monitor ambient conditions that carbureted engines could not compensate for. As a result,
the fuel supply is more accurate.
Fig. 1-16
MMMTC VER 1 1 - 8
1. OUTLINE OF MPI SYSTEM
(3) Actuators
Actuators are devices that the Engine-ECU operates to carry out control decisions. The op-
eration of actuators determines the amount of fuel supply, ignition timing, idle speed and
resulting emissions.
If the Engine-ECU wants to increase engine idle speed, the Engine-ECU pulses the idle
speed control servo (an actuator) to increase the amount of air flow through the throttle
valve.
Most actuators do not provide feedback input to the Engine-ECU, because actuators perform
their operations based on circuit connections made by the Engine-ECU.
Fig. 1-17
4. KNOWLEDGE CHECK
Evaluate the following sentences and determine if they are correct or incorrect. Then make
the required correction to the wrong portion in the incorrect sentence.
(1) The stoichiometric air-fuel ratio is said to be 14.7:1 in the comparison of their cubic vol-
ume.
(2) MPI system can be sorted two types according to the air flow sensor that detects the in-
take air volume, the mass flow type and the speed density type.
(3) The fuel pump is mounted in the fuel tank and immersed in the fuel, it offers the ad-
vantages that its operating sound is sealed off and that the possibility of vapor lock is re-
duced.
(4) Engine-ECU uses information from various actuators to calculate the optimum fuel injec-
tion timing & amount, the ignition timing, and the idling speed. The ECU issues drive signals
to the relevant sensors in accordance with the results of its calculations.
1 - 9 MMMTC VER 1
2. SYSTEM COMPONENTS
1. SYSTEM CONFIGURATION
Figure 2-1 shows the MPI control system diagram which is employed on the LANCER-EX
(CY4A) with 4B1 engine with a single oxygen sensor. MMMTC VER1
Fig. 2-1
2 - 1
2. SYSTEM COMPONENTS
2. LOCATION OF COMPONENTS
The location of sensors, actuators and ECUs used in 4B1 MPI system are shown below.
Name Symbol Name Symbol
Accelerator pedal position sensor Exhaust oil feeder control valve
X B
A/C compressor relay Ignition coil
I (with the built-in power transistor) D
Air flow sensor Injector
(with intake air temp. sensor) R K
Crank angle sensor Injector relay
C I
Detonation sensor Intake camshaft position sensor
N Q
Diagnosis connector Exhaust camshaft position sensor
V F
Electronic-controlled throttle valve Intake oil feeder control valve
P A
(TPS and throttle valve control servo)
Engine control relay Manifold absolute pressure sensor
I L
Engine coolant temperature sensor Oxygen sensor
G E
<Vehicles with single oxygen sensor>
Engine-ECU Power steering fluid pressure switch
H J
Engine oil pressure switch Purge control solenoid valve
M O
Engine warning lamp Starter relay
W I
ETACS-ECU (Fuel pump relay) Throttle valve control servo relay
U Fig. 2-2 I
MMMTC VER 1
2 - 2
2. SYSTEM COMPONENTS
3. ENGINE-ECU
The Engine-ECU provides an output to the actuator based on the input information from the
sensors, and the data that is programmed into the memory. The Engine-ECU has the fol-
lowing four types of memory: Fig. 2-3
◆ Read Only Memory (ROM)
- Preprogrammed information
- Does not change during operation
- Does not require battery power to retain the data
ROM contains permanently stored information which is programmed by the manufacture
and it is not changed during Engine-ECU operation. Battery power is not required to main-
tain ROM data. The Engine-ECU uses ROM data to produce an output based on an input.
◆ Random Access Memory (RAM)
- Engine-ECU can read or write
- Temporary storage for sensor data
- Stored using battery voltage
The Engine-ECU can either read information from, or store it in RAM. RAM stores data from
sensor output temporarily until it is used or updated. Some information stored in RAM is also
used to update the permanent program stored in ROM using direct battery voltage so it is
not lost when the ignition switch is turned off. If battery power is lost for any reason, upon
initial start-up, the Engine-ECU will operate according to ROM instructions only until new
data is stored in RAM during operation.
◆ Adaptive Memory
- Part of RAM
- Stores “learned” information
- If battery is disconnected, learned information is lost
Adaptive memory is the ability of the Engine-ECU to update its internal program to compen-
sate for the engine actual operational conditions. For example, RAM updates the original
program stored in ROM based on “learned” information gathered from normal operating con-
ditions, to compensate for worn components or long term changes in air-fuel management
requirements. As a result, the Engine-ECU “learns” to adapt to the changing engine condi-
tions over time. This “learned” information is stored in RAM, and it is retained in memory as
long as the vehicle’s battery is connected. If the battery is disconnected for any reason, the
Engine-ECU must “re-learn” actual operational conditions all over again.
◆ Flash Memory (EEP-ROM; Electrical Erasable Programmable -Read Only Memory)
- Rewrite or up-date the pre-programmed information
EEP-ROM is a non-volatile type of memory which contents can be electrically erased and
rewritten repeatedly. The program in the Engine-ECU uses a flash memory which can be
updated using the MUT. 2 - 3 MMMTC VER1
2. SYSTEM COMPONENTS
4. SENSOR
((((1) Air Flow Sensor (AFS)
The AFS is installed in the air intake hose, and it is
composed of an extremely small heat sensing re-
sistor. The AFS controls the amount of electric cur-
rent flowing into the heat sensing resistor to keep it
at a constant temperature. When air flows through
the sensor, it removes the heat from the sensing
element. To maintain the temperature in the sen-
sor, the AFS increases the electric current. The
more air that flows through, the more current it will
Therefore, the air flow sensor increases the amount of electric current to the heat sensing
resistor. Thus, the amount of electric current increases in accordance with the air mass flow
rate. The air flow sensor measures the air mass flow rate by detecting the amount of electric
current. The air flow sensor amplifies the detected electric current amount and outputs it
into the Engine-ECU. The Engine-ECU uses this output current and engine speed to calcu-
Fig. 2-4
be necessary to keep the element heated up.
late and output basic fuel injection time. Sensor properties are as shown in the figure 2-5.
(2) Intake Air Temperature Sensor (IAT)
The intake air temperature sensor is built in to the
air flow sensor. The IAT is a thermistor resistance
which changes its value of internal resistance ac-
cording to temperature. Changing the resistance
value also changes the value of the voltage drop
Fig. 2-5
across the sensor. The Engine-ECU uses this out-
put voltage drop to compensate for fuel injection
control and ignition timing control. Sensor proper-
ties are as shown in the figure 2-7.
Fig. 2-6
Fig. 2-7
MMMTC VER 1
2 - 4
2. SYSTEM COMPONENTS
(3) Manifold Absolute Pressure Sensor (MAP)
The manifold absolute pressure sensor is installed in
the intake manifold plenum. Manifold absolute pres-
sure sensor uses a piezo resistive semiconductor to
output to the Engine-ECU a voltage drop value that
varies according to manifold absolute pressure. The
Engine-ECU uses this output voltage to compensate
for fuel injection volume according to manifold abso-
lute pressure. Sensor properties are as shown in
figure 2-9.
Fig. 2-8
<Piezo resistance effect>
Engine-ECU
The electrical resistance of a piece of metal
MAP sensor
changes when the metal’s length and cross- sec-
tional area change as a result of strain. Likewise,
the electrical resistance of a semiconductor
changes greatly when the symmetry of crystals in
Fig. 2-9
the semiconductor is changed by the application
of pressure. This phenomenon is called the piezo
resistance effect.
(4) Engine Coolant Temperature Sensor (ECT)
5v
The engine coolant temperature sensor is installed
in the thermostat housing. The ECT sensor uses a
thermistor which changes the values of the resis-
tance according to coolant temperature. A voltage
drop is generated across the sensor, and the output
Fig. 2-10
voltage goes to the Engine-ECU. The Engine-ECU
uses this output voltage to appropriately control fuel
injection volume, idle speed and ignition timing. Sen-
sor properties are as shown in the figure 2-12.
Fig. 2-11
Fig. 2-12
MMMTC VER1
2 - 5
2. SYSTEM COMPONENTS
(5) Throttle Position Sensor (TPS)
The throttle position sensor is installed in the throttle
body. The TPS outputs a voltage value to the Engine
-ECU based on the position of the throttle shaft rota-
tion angle. The Engine-ECU uses this signal to de-
tect the throttle valve opening angle to perform throt-
tle valve control servo feedback control. This throttle
position sensor uses Hall IC and is a non-contact
type.
<Structure & System>
The throttle position sensor is composed of a perma-
nent magnet fixed on the throttle shaft, a Hall IC that
outputs voltage according to magnetic flux density
and a stator that efficiently introduces magnetic flux
from the permanent magnet to the Hall IC.
Fig. 2-13
Magnetic flux (B)
The Hall element is a semiconductor element that
employs the Hall effect. It can be used to indicate
the density and polarity of a magnetic flux.
The Hall element behaves as follows: When a cur-
Fig. 2-14
rent (IH) goes through the Hall element and mag-
netic flux of density (B) is generated in the direction
perpendicular to the direction of the current as
shown in Fig. 2-15, an electromotive force (VH) is
<Hall Element>
developed across the output terminals c and d.
This output is proportional to the magnetic flux den-
sity (B).
Fig. 2-15
MMMTC VER 1
2 - 6
2. SYSTEM COMPONENTS
The magnetic flux density at the Hall IC is propor-
tional to the output voltage.
Throttle position sensor has 2 output voltages to the
Engine-ECU - throttle position sensor (main) and
throttle position sensor (sub). When the throttle
valve turns, the output voltages of throttle position
sensors main and sub changes with the movement
of the shaft. This allows the Engine-ECU to detect
actual throttle opening angle. The Engine-ECU uses
this output voltage for feedback control of the throttle
valve control servo. The Engine-ECU also compares
the output voltages of the throttle position sensor
(main) and throttle position sensor (sub) to check for
abnormality in the throttle position sensor.
The relationship between throttle opening angle and
output voltage of the throttle position sensor (main)
and throttle position sensor (sub) is as shown in fig-
ure 2-17.
Fig. 2-16
(6) Accelerator Pedal Position Sensor (APS)
The accelerator pedal position sensor is integrated
with the accelerator pedal, and detects accelerator
pedal depression angle. The Engine-ECU uses the
output voltage of this sensor to control the appropri-
ate throttle valve opening angle and the fuel injection
Fig. 2-17
volume. This accelerator pedal position sensor uses
a Hall IC and it is a non-contact type. MMMTC VER1
Fig. 2-18
2 - 7
2. SYSTEM COMPONENTS
<Structure & System>
The accelerator pedal position sensor is composed
of a permanent magnet fixed on the magnet carrier
of the pedal shaft. The Hall IC outputs voltage ac-
cording to a magnetic flux density and a stator that
efficiently introduces magnetic flux from the perma-
nent magnet to a Hall IC.
The magnetic flux density at the Hall IC is propor-
tional to the output voltage.
The accelerator pedal position sensor has 2 output
voltages to the Engine-ECU; one is from accelerator
pedal position sensor (main) and the other from ac-
celerator pedal position sensor (sub). According to
the depression of the accelerator pedal, output volt-
Fig. 2-19
ages of the accelerator pedal position sensors main
and sub changes, allowing the Engine-ECU to detect
the actual accelerator pedal depression amount. The
Engine-ECU uses accelerator pedal position sensor
(main) output voltage for appropriate throttle valve
opening angle control and fuel injection volume con-
trol. The Engine-ECU also compares output voltage
of the accelerator pedal position sensor (main) and
accelerator pedal position sensor (sub) to check for
abnormality in the sensor. The relationship between
accelerator opening angle and output voltage of the
accelerator pedal position sensor (main) and accel-
erator pedal position sensor (sub) is as shown in the
figure 2-21.
Fig. 2-20
Fig. 2-21
MMMTC VER 1
2 - 8
2. SYSTEM COMPONENTS
(7) Oxygen Sensor (O2 Sensor)
Oxygen sensors are installed in upstream and
downstream (vehicles with dual oxygen sen-
Electromotive force
sors) of the catalytic converter. The Oxygen
V sensor has a built-in heater which helps in
early activation of the sensor to enable feed-
back control of air-fuel ratio soon after the en-
Outside air Platinum electrode gine has started.
The solid electrolyte (zirconia element) shown
(open air side)
in Fig. 2-22 produces an electromotive force
Solid electrolyte
(Zirconia element) when there is a difference between the oxygen
concentration at its inside surface (which is
Platinum electrode exposed to the exhaust gases) and the oxygen
Exhaust gas (exhaust gas side)
concentration at its outside surface (which is
Coating (ceramics)
exposed to the outside air). When the oxygen
concentration in the exhaust gases is relatively
low, a large quantity of oxygen ions moves from
the outside-air side to the exhaust-gas side.
This movement of oxygen ions causes an
electromotive force to be produced between
the outside-air-side electrode and the exhaust-
gas-side electrode.
This sensor uses the oxygen concentration cell prin-
Fig. 2-22
ciple of solid electrolyte (zirconia) and displays the
property of sudden change in output voltage near
theoretical air-fuel ratio. This property is used to de-
tect oxygen density in the exhaust gas. Feedback to
the Engine-ECU allows it to judge whether air-fuel
ratio is rich or lean when comparing to the theoreti-
cal air-fuel ratio.
Purification ratio The output voltage of the O2 sensor provides the En-
gine-ECU with a precise feedback control where the
theoretical air-fuel ratio is matched to the best clean-
ing efficiency of 3-way catalytic converter.
Fig. 2-23
Fig. 2-24
Fig. 2-25
MMMTC VER1
2 - 9
2. SYSTEM COMPONENTS
(8) Crank Angle Sensor (CAS)
The crank angle sensor is installed on the right side
of the cylinder block. It produces an output pulse
signal in combination with a crankshaft sensing ring
(36 teeth including 3 missing teeth) when the crank-
shaft is rotating. The ring is installed on the crank-
shaft. The output pulse signal is a 0-5 voltage fre-
quency to the Engine-ECU which varies with engine
speed. The Engine-ECU uses crank angle sensor’s
output pulse to detect crankshaft position.
The crank angle sensor uses a magnetic resistance
element. When the vane of the crankshaft-sensing
ring passes the front surface of the magnetic resis-
tance element, the flux from the magnet passes the
magnetic resistance element. Thus, resistance of the
magnetic resistance element increases. When the
vane of the crankshaft-sensing ring does not pass
Fig. 2-26
the front surface of the magnetic resistance element,
the flux from the magnet does not pass the magnetic
resistance element and the resistance decreases.
The crank angle sensor converts this change in re-
sistance of the magnetic resistance element and
turns an internal transistor ON-OFF causing the 5
volts in the ECU to pulse between 0 and 5 volts.
This is considered output to the Engine-ECU.
<<<<Calculation of engine speed>
The engine speed can be calculated by measur-
ing the interval between one pulse of crank angle
sensor signal and another as shown in Fig. 2-29.
Fig. 2-27
Fig. 2-28
60 sec.
N rpm =
36 x T sec.
Fig. 2-29
MMMTC VER 1
2 - 10
2. SYSTEM COMPONENTS
(9) Camshaft Position Sensor
<Intake Camshaft Position Sensor>
The intake camshaft position sensor is installed on
the left side of the cylinder head. The intake cam-
shaft position sensor works in combination of the
half-moon sensing portion of the camshaft to gener-
ate a pulse signal inside the Engine-ECU. The En-
gine-ECU uses the feedback pulsations to optimize
the phase of the intake camshaft. The Engine-ECU
also uses a combination of the camshaft position
sensor output pulse signal and the crankshaft posi-
tion sensor output pulse signal to identify cylinders in
the compression process.
The intake camshaft position sensor uses a mag-
netic resistance element. When the camshaft posi-
tion sensing portion passes the front surface of the
magnetic resistance element, the flux from the mag-
net passes the magnetic resistance element. Thus,
Fig. 2-30
resistance of the magnetic resistance element in-
creases. When the camshaft position sensing por-
tion does not pass the front surface of the magnetic
resistance element, the flux from the magnet does
not pass the magnetic resistance element and the
resistance decreases. The intake camshaft position
sensor converts this change in resistance of the
magnetic resistance element and turns an internal
transistor ON-OFF causing the 5 volts in the ECU to
pulse between 0 and 5 volts.
<Exhaust Camshaft Position Sensor>
The exhaust camshaft position sensor is installed on
the right side of the cylinder head. The exhaust
crankshaft position sensor works in combination with
the half-moon shape portion to generate a voltage
pulse signal inside the Engine-ECU. The Engine-
ECU uses the feedback signal to optimize the phase
of the exhaust camshaft. The structure and opera-
tion of this sensor are basically the same as that of
the intake camshaft position sensor. MMMTC VER1
Fig. 2-31
Fig. 2-32
2 - 11
2. SYSTEM COMPONENTS
(10) Detonation Sensor (Knock Sensor)
A detonation sensor is installed on the cylinder
block. The Detonation sensor uses a piezoelectric
element to convert the vibration of the cylinder block
generated when the engine is in operation to a min-
ute voltage that is output to Engine-ECU. The En-
gine-ECU uses the feedback voltage to detect en-
gine knocking. The Engine-ECU retards the ignition
timing according to the strength of the knocking to
reduce the possibility of internal engine damage.
Fig. 2-33
(11) Barometric Pressure Sensor
A barometric pressure sensor is built into the Engine
-ECU. The barometric pressure sensor is a semicon-
ductor diffused pressure element which outputs volt-
age to the Engine-ECU according to atmospheric
pressure. The Engine-ECU uses this output voltage
Fig. 2-34
to determine the altitude of vehicle operation, and
compensates the fuel injection volume to achieve
the appropriate air-fuel ratio for that altitude.
(12) Vehicle Speed Sensor <M/T>
A vehicle speed sensor is installed in the output
shaft of the manual transmission. The sensor uses a
Hall IC in combination with the rotation of the speed-
ometer drive gear to create a pulse voltage that is
output to Engine-ECU. The Engine-ECU calculates
Fig. 2-35
vehicle speed based on the vehicle speed sensor’s
output frequency. Sensor properties are as shown in
the figure 2-37.
Fig. 2-36
Fig. 2-37
MMMTC VER 1
2 - 12
2. SYSTEM COMPONENTS
(13) Engine Oil Pressure Switch
The engine oil pressure switch is installed on the
left side of the cylinder block, and detects whether
the oil pressure is high or low using the contact
switch. When the engine is OFF the contact switch
is closed and the warning light in the combination
meter is ON. But when the engine is started, oil
pressure opens the contact switch and the light in
the combination meter is turned OFF.
The Engine-ECU outputs the ON-OFF signal to the
combination meter through the CAN BUS.
Fig. 2-38
(14) Alternator FR Terminal
The alternator turns ON/OFF the power transistor in the voltage regulator to adjust current
flow in the field coil according to alternator output current. This way the alternator output
voltage is kept adjusted to about 14.4 volts. The ratio of the power transistor ON time (ON
duty) is output from alternator FR terminal to the Engine-ECU. The Engine-ECU uses this
signal to detect alternator output current and drives the throttle valve control servo accord-
Fig. 2-39
ing to output current (electric load). This prevents change in idle speed due to electric load
and helps maintain a stable idle speed. Fig. 2-40 MMMTC VER1
2 - 13
2. SYSTEM COMPONENTS
(15) Alternator L Terminal
After turning ON the ignition switch, current from the Engine-ECU is sent to the alternator L
terminal. This allows the voltage regulator to be ON and the field coil to be excited. When
the alternator rotates, the voltage is excited in the stator coil and the current is output from B
-terminal through the commutation diode. Also the generated voltage is input to the voltage
regulator through the commutation diode. After the electric generation begins, the current is
supplied to the field coil from this circuit. In addition, the generated voltage is output from
the alternator L terminal to the Engine-ECU. This allows the Engine-ECU to detect that the
electric generation begins. The Engine-ECU outputs the ON signal to the combination meter
through the CAN and then turns off the charge lamp.
Fig. 2-41
MMMTC VER 1
2 - 14
2. SYSTEM COMPONENTS
5. ACTUATOR
(1) Injector
An injector is an injection nozzle with an electro-
magnetic valve that controls fuel delivery when the
Engine-ECU makes the ground connection. One
injector is installed in the intake manifold of each
cylinder and it is fixed to the delivery pipe. When
electrical current flows through the solenoid coil, a
magnetic field is created that rises the plunger
against spring tension. The ball valve is integrated
with the plunger, and it gets pulled together with the
plunger to fully open the injection delivery hole. The
fuel pump the forces the fuel through the injector.
Voltage from the battery positive is applied from the
injector relay to the injector, and up to the Engine-
ECU. When needed, the Engine-ECU turns ON
any of the power transistors to complete the injec-
tor’s ground circuit. Thus, current flows through the
injector while power transistor is ON and the injec-
tor delivers the fuel.
Fig. 2-42
pick-up point where the injector
drive signal waveform is ob-
served. MMMTC VER1
Fig. 2-43
2 - 15
2. SYSTEM COMPONENTS
(2) Throttle Valve Control Servo
A throttle valve control servo is installed in the throt-
tle body. The throttle valve control servo performs
the Opening/Closing of the throttle valve through a
reduction gear. The Engine-ECU changes current
direction according to the need for Opening/Closing
of the valve. The Engine-ECU operates the servo
motor in Pulse Width Modulation (PWM) to hold the
throttle valve open/close at a steady point .
The throttle valve control servo is composed of a
good response, low energy, and small brush DC
motor, and can generate rotation force correspond-
ing to the current applied on the coil. When there is
no current passing through the throttle valve control
servo, the throttle valve remains at a prescribed
Fig. 2-44
opening angle as a result of spring tension. So,
even if current stops because of a fault in the sys-
tem, a minimum level of engine operation will be
possible.
Fig. 2-45
Fig. 2-46
MMMTC VER 1
2 - 16
2. SYSTEM COMPONENTS
(3) Ignition Coil
The ignition coil is the plug-top type and it is in-
stalled on the top of the cylinder head. A power
transistor is built into the ignition coil assembly, and
the Engine-ECU drives the power transistor to con-
trol the flow of primary current.
<Power Transistor>
The power transistor is designed to handle the rela-
tively high current (5 A is typical) that flows through
the ignition coil primary winding to ground.
The power transistor connects and disconnects to
ground the ignition coil primary winding when the
Engine-ECU connects the base of the transistor.
Fig. 2-47
When 5 V is applied to the base of the transistor,
the collector-emitter junction of the transistor be-
comes conductive and current flows through the
ignition coil primary winding to ground. When the
Engine-ECU switches off the 5 V supply to the
base, the collector-emitter junction of the transistor
becomes non-conductive and current flow through
the primary winding is interrupted.
When monitoring the voltage at the base of the power transistor with an oscilloscope, it pro-
duces the voltage waveform that is shown in the figure 2-49. MMMTC VER1
Fig. 2-48
Fig. 2-49
2 - 17
2. SYSTEM COMPONENTS
(4) Purge Control Solenoid Valve
The purge control solenoid valve connects via vac-
uum hoses the canister and the intake manifold.
When the valve is ON, it allows the fuel vapor gas
from the tank that is stored in the canister to be
sucked in the intake manifold for proper burning.
The purge control solenoid valve is a duty control
type solenoid valve. The Engine-ECU changes the
ON duty ratio according to engine’s operating con-
dition to control the intake volume of fuel vapor gas.
Fig. 2-50
(5) Intake Oil Feeder Control Valve
The intake oil feeder control valve is installed on the
left side of the cylinder head. It receives a duty sig-
nal from the Engine-ECU, and the intake oil feeder
control valve moves the spool valve position. De-
pending on the location of the spool valve, oil pres-
Fig. 2-51
sure from the oil pump is delivered into the ad-
vanced chamber or the retarded chamber of the
V.V.T. sprocket to continually change the intake cam-
shaft phase. The spring makes spool valve stop at
the position where the intake camshaft is at the most
retarded angle when the engine is stopped.
The Engine-ECU moves the spool valve position by
increasing and decreasing ON duty cycle of the in-
take oil feeder control valve and allows the intake
camshaft to be at the target phase angle. When the
duty ratio increases, the spool valve moves to rotate
the sprocket toward the advanced angle side. When
the duty ratio decreases, the sprocket rotates toward
Fig. 2-52
the retarded angle side. When the valve is at me-
dium duty ratio, all the oil passages are closed, and
AK700721AB
the spool valve achieves the medium position. This
allows the phase angle to be kept constant. The En-
gine-ECU changes and controls the duty ratio in ac-
cordance with the engine operation to get the opti-
mum phase angle.
Fig. 2-53
MMMTC VER 1
2 - 18
2. SYSTEM COMPONENTS
(6) Exhaust Oil Feeder Control Valve
The exhaust oil feeder control valve is installed on
the right side of the cylinder head. Receiving the
duty signal from the Engine-ECU, the exhaust oil
feeder control valve moves the spool valve position
and directs the oil pressure from the oil pump into
the advanced chamber or the retarded chamber of
the V.V.T. sprocket to continually change the ex-
haust camshaft phase. The spring makes the spool
valve stop at the position where the exhaust cam-
shaft is at the most advanced angle when the engine
is stopped.
The Engine-ECU moves the spool valve position by
increasing and decreasing the ON duty ratio of the
exhaust oil feeder control valve, allowing the exhaust
camshaft to be at the target phase angle. When the
duty ratio increases, the spool valve moves. The
sprocket rotates toward the retarded angle side.
When the duty ratio decreases, the sprocket rotates
toward the advanced angle side. When the medium
Fig. 2-54
duty ratio is achieved, all the oil passages are
closed, and the spool valve is at the medium posi-
AK700722AB
tion. This allows the phase angle to be kept con-
stant. The Engine-ECU changes and controls the
duty ratio in accordance with the engine operation to
get the optimum phase angle.
(7) Alternator G Terminal
The Engine-ECU sends ON/OFF signal to alternator G terminal in order to control alternator
output voltage. When the power transistor in the Engine-ECU turns ON, the output voltage
Fig. 2-55
is regulated to about 12.8 V, becoming lower than the battery voltage and almost no current
is supplied from the alternator. On the other hand, when the power transistor in the Engine-
ECU turns OFF, the output voltage is regulated to about 14.4 V, supplying current to the
electrical load.
In case the electric load increases suddenly, the Engine-ECU controls alternator output volt-
age by sending an ON signal to the G terminal in order to suppress the sudden alternator
load increase, and thus prevents the fluctuation of the engine idle speed. MMMTC VER1
Fig. 2-56
2 - 19
2. SYSTEM COMPONENTS
6. KNOWLEDGE CHECK
Regarding the following sentences of the components used on 4B1MPI system, identify
them between correct or incorrect. And make required correction to the wrong portion in the
incorrect sentence.
(1) Air flow sensor measures the mass flow rate of the intake air, and outputs it to the En-
gine-ECU.
(2) Intake air temperature sensor detects exhaust gas temperature through thermistor’s re-
sistance change and outputs the voltage according to exhaust gas temperature to Engine-
ECU.
(3) Manifold absolute pressure sensor uses a piezo resistive semiconductor to output the
voltage according to manifold absolute pressure to Engine-ECU.
(4) Engine coolant temperature sensor uses thermistor’s resistance change to detect engine
oil temperature.
(5) Throttle position sensor is used to detect the throttle valve opening angle.
(6) Accelerator pedal position sensor is used to detect the throttle valve opening angle.
(7) Accelerator pedal position sensor is composed of a permanent magnet fixed on the
pedal shaft and Hall IC element.
(8) Engine-ECU can perform precise feedback air-fuel ratio utilizing the knock sensor output
in order to activate the 3-way catalytic converter most effectively.
(9) Engine-ECU uses crank angle sensor’s output pulse to detect crankshaft position.
(10) Engine-ECU uses a combination of the intake camshaft position sensor output and
crankshaft position sensor output to identify cylinders in the intake stroke.
(11) Engine-ECU uses the detonation sensor to detect knocking, and compensates the igni-
tion timing lag according to the strength of the knocking.
(12) Barometric pressure sensor is built into Engine-ECU. The Engine-ECU uses this sen-
sor to sense the vehicle weight.
(13) Engine oil pressure switch detects whether the oil pressure is high or low using the
contact switch.
(14) Injector is installed at the top of each combustion chamber and connected to the deliv-
ery pipe.
(15) Throttle valve control servo uses a DC motor to open/close the throttle valve.
(16) In the ignition system, Engine-ECU drives the power transistor to control the flow of
secondary current to the ignition coil.
(17) Purge control solenoid valve controls the intake volume of fuel vapor gas from the can-
ister, the solenoid valve is a duty controlled by the Engine-ECU.
(18) Engine-ECU drives the intake oil feeder control valve, and it allows the exhaust cam-
shaft to be at the target phase angle.
(19) Engine-ECU drives the exhaust oil feeder control valve, and it allows the exhaust cam-
shaft to be at the target phase angle.
(20) Engine-ECU sends OFF signal to alternator G terminal in order to set lower the regula-
tor voltage than the battery voltage. 2 - 20
MMMTC VER 1
3. MPI SYSTEM
1. FUEL INJECTION CONTROL
The volume of fuel injection has to be regulated to achieve the optimum air-fuel ratio in ac-
cordance with the constant changes in engine operation & driving conditions. Fuel injection
volume is mainly controlled by injector drive time, or the amount of time that the Engine-
ECU keeps the injector connected to ground. There is a prescribed basic drive time that
varies according to the engine speed and intake air volume, and the Engine-ECU compen-
sates the basic drive time according to operational conditions such as changes in tempera-
ture, manifold pressure, pressure on the accelerator pedal, crankshaft and/camshaft posi-
tion, oxygen content, and engine detonation. Fuel injection is provided individually for each
cylinder once every two engine rotations, in a sequential fashion, and following the firing
order. This fuel injection type is called Multi Points Fuel Injection, or MPI for short, and it is
the system used in MMC vehicles with gasoline engines.
<System Configuration Diagram>
Fig. 3-1
3 - 1 MMMTC VER 1
3. MPI SYSTEM
(1) Fuel Injection Timing Control
The injector drive timing of the MPI system is controlled in the following manner according
to driving conditions.
◆ Sequential Injection <Fuel Injection During Cranking and Normal Operation>
Fig. 3-2
Fuel injection is delivered to each cylinder at precise timing while the piston in that cylinder
is in the exhaust stroke. The Engine-ECU compares the crank angle sensor output pulse
signal, the intake camshaft position sensor output pulse signal and the exhaust camshaft
position sensor output pulse signal to identify the cylinder, the stroke, and the position of the
piston. Using these as a reference, it performs sequential injection following engine firing
order 1-3-4-2 as in the case of a 4-cylinder engine.
◆ Simultaneous Injection <Additional Fuel Injection During Acceleration>
Fig. 3-3
In addition, fuel volume is injected according to the extent of the acceleration.
MMMTC VER 1 3 - 2
3. MPI SYSTEM
(2) Fuel Injection Volume (Injector Drive Time) Control
The figure below shows the flow chart of calculating the injection amount for normal operat-
ing conditions. Basic injector drive time is established based on the air flow sensor signal
(intake air volume signal) and the crankshaft position sensor signal (engine rotation signal).
This basic drive time is compensated according to signals from various sensors and optimum
injector drive time, which delivers the optimal fuel injection volume, is calculated according to
driving conditions.
<Fuel Injection Volume Control Block Diagram> (Normal Operation)
Fig. 3-4
3 - 3 MMMTC VER 1
3. MPI SYSTEM
1) Basic Fuel Injection Time Determination
The basic fuel injection time refers to the amount of drive time the fuel injector is ON in or-
der to achieve theoretical air-fuel ratio for the air volume during the intake stroke. Fuel injec-
tion volume also changes according to the pressure difference (injected fuel pressure) be-
tween manifold pressure and fuel pressure (constant). So, injected fuel pressure compensa-
tion is considered in the calculation of the basic fuel injection time.
Basic fuel Intake air amount per cycle per cylinder Fuel injection pressure
injection time ∝ X compensation
Theoretical air-fuel ratio
The Engine-ECU calculates intake air volume of each cycle for 1 cylinder based on the air-
flow sensor signal and the crank angle sensor signal. Also, during engine cranking, the map
value prescribed by the coolant temperature sensor signal is used to establish basic fuel in-
jection time.
2) Injector Drive Time Compensation
After calculating the injector basic fuel injection time, the Engine-ECU makes the following
compensations to control the optimum fuel injection volume according to driving conditions.
Compensations Content
Oxygen sensor feed- The Oxygen sensor signal is used for making air-fuel ratio compensa-
back compensation tion that produces the best cleaning efficiency of the 3-way catalytic
converter. This compensation is sometimes ignored depending on
driving conditions, like for instance wide open throttle operation.
Air-fuel ratio compen- Under driving conditions where oxygen sensor feedback compensa-
sation tion is not performed, compensation is made based on pre-set map
values that vary according to engine speed and intake air volume.
Engine coolant tem- Compensation is made according to the engine coolant temperature.
perature compensa- The lower the engine coolant temperature, the greater the fuel injec-
tion tion volume.
Acceleration/ Decel- Compensation is made according to change in intake air volume. Dur-
eration compensation ing acceleration, fuel injection volume is increased. Also, during decel-
eration, fuel injection volume is decreased.
Intake air tempera- Compensation is made according to the intake air temperature. The
ture compensation lower the intake air temperature, the greater the fuel injection volume.
Atmospheric pres- Compensation is made according to the atmospheric pressure. The
sure compensation lower the atmospheric pressure, the smaller the fuel injection volume.
Fuel injection com- Compensation is made according to the pressure difference between
pensation atmospheric pressure and manifold absolute pressure. The greater
the difference in pressure, the shorter the injector drive time.
Battery voltage com- Compensation is made depending on battery voltage. The lower the
pensation battery voltage, the greater the injector drive signal time.
Learning value for Compensation amount is learned to compensate feedback of oxygen
fuel compensation sensor. This allows system to compensate in accordance with engine
characteristics.
MMMTC VER 1 3 - 4
3. MPI SYSTEM
<Air/fuel Ratio Compensation>
Correction is achieved according to a
map value set for each engine speed and
corresponding to engine load (A/N).
* Map value:
(A/N) Correction
coefficient A value pre-set and pre-stored in the
ROM in the ECU
Engine speed (rpm)
Fig. 3-5
<Oxygen Sensor Feedback Compensation>
A three-way catalytic converter can effectively oxidize CO and HCs, and reduce NOx simul-
taneously, converting them into harmless CO 2, water (H 2O), oxygen (O 2), and nitrogen (N 2),
when the air/fuel ratio is kept as close as possible to the stoichiometric ratio of 14.7:1.
The oxygen sensor signal, as graphed in figure 3-6, is the feedback control used to achieve
and maintain the stoichiometric air/fuel ratio. When the air/fuel mixture is richer than the
stoichiometric ratio, there is less oxygen in the exhaust gas and thus the oxygen sensor out-
put voltage is higher, providing a “rich mixture” signal as input to the Engine-ECU. The En-
gine-ECU responds by decreasing the amount of fuel injected. If the air/fuel ratio decreases
to the point that and the mixture becomes leaner than the stoichiometric ratio, the oxygen
concentration in the exhaust gas increases and the oxygen sensor output voltage is lower,
providing a “lean mixture” signal as input to the Engine-ECU. The Engine-ECU responds by
increasing the amount of fuel injected. The Engine-ECU controls the fuel injection amount
so that the air-fuel mixture is maintained at the stoichiometric ratio.
Under the following specific conditions, this compensation is not performed.
● While cranking the engine
● During engine warm-up when engine coolant temperature is less than 45°C
● During acceleration/deceleration
● During high load operation
● When oxygen sensor is not functioning
Fig. 3-6
3 - 5 MMMTC VER 1
3. MPI SYSTEM
- Learning Control -
The feedback control alone cannot always correct the air/fuel ratio optimally. For example,
the center of the feedback control correction range can change over time as shown in Fig.
3-7 due to changes in the characteristics of system components, thus narrowing the
range over which the Engine-ECU can make corrections. To counteract this phenome-
non, the Engine-ECU forces the correction center value back to the center of the available
range. This type of control is known as learning control that is composed of short term and
long term trims. The short term trim represents changes in the fuel injector drive time to
maintain a stoichiometric air/fuel ratio. The long term trim works to bring the variation of
the short term trim to be within the pre-determined range. The long term trim resumes to
this level of the injector drive time compensation at the next time when the vehicle is op-
erated in the same operating zone. It is in this way that the Engine-ECU is continuously
relearning the most appropriate level of control, even as the vehicle ages, engine internal
parts wear and operating condition change.
Correction impossible
Range of correction
Long term trim
Short term trim
Fig. 3-7
<Engine Coolant Temperature Compensation>
The degree of the compensation is high when the coolant temperature is low. The intake
and exhaust valves and cylinder walls are still cool when the engine coolant is still cool
even if the air/fuel mixture in the cylinders burns completely. To compensate for insufficient
vaporization of fuel during warm-up, the Engine-ECU continues to perform enrichment of
the air/fuel mixture until the engine coolant temperature rises to a predetermined level.
<Acceleration/Deceleration Compensation>
● Control during acceleration
When the engine is accelerated, fuel is injected for
the time suitable for the changed depressing de-
gree of the accelerator pedal.
Accelerator pedal stroke ● Control during deceleration
During decelerated operation as on a downhill,
fuel cut control is achieved to prevent the cata-
lyst temperature from rising excessively and im-
prove fuel economy.
Fig. 3-8
MMMTC VER 1 3 - 6
3. MPI SYSTEM
- Fuel cut control for over-limit RPM
When engine speed exceeds the prescribed limit of
6,800 r/min, the Engine-ECU cuts fuel supply to
Idling In racing state prevent overrunning and thus protect the engine
from mechanical damage.
(A/N)
Fuel cut zone Accel’ pedal: OFF
1,000 2,000 3,000
Engine speed (rpm)
Fig. 3-9
<Intake Air Temperature Compensation>
The air/fuel ratio must be corrected in accordance with the intake air temperature. The de-
gree of compensation is high when the intake air temperature is low and vice-versa.
Air volume drawn into each cylinder is relatively constant, but the air mass changes in ac-
cordance with the air temperature. For example, a decrease in the ambient temperature
makes the air’s density higher, resulting in an increase in the air’s mass. The air/fuel ratio
increases accordingly, making a lean mixture.
<Atmospheric Pressure Compensation>
The air/fuel ratio must be corrected in accordance with the barometric pressure. The de-
gree of compensation is high when the barometric pressure is high and vice-versa.
Air volume drawn into each cylinder is relatively constant, but the air mass changes in ac-
cordance with vehicle altitude. For example, an increase in the barometric pressure makes
the air’s density higher, resulting in an increase in the air’s mass. The air/fuel ratio increas-
es accordingly, making a lean mixture.
<Battery Voltage Compensation>
The target air-fuel ratio takes into consideration a battery voltage compensation (Fig. 3-10).
The injector opens its valve in response to a drive signal from the Engine-ECU. However,
an operational lag on the injector drive signal takes place depending on battery voltage,
making the actual valve opening time to be shorter than the injector drive signal interval.
Therefore, Fig. 3-11 shows how the battery voltage compensation value changes in ac-
cordance with the battery voltage.
Compensation value (msec)
ON
Drive signal OFF
Valve operational lag
Opened
Injector Closed
Valve opening time Battery voltage (v)
Fig. 3-10 Fig. 3-11
3 - 7 MMMTC VER 1
3. MPI SYSTEM
2. IGNITION CONTROL
A distributor-less ignition system is used in the current Mitsubishi MPI systems as shown in
figure 3-12. Each cylinder has a respective ignition coil assembly which combines a dedi-
cated power transistor that is controlled by the Engine-ECU. The end of the secondary igni-
tion coil winding has been directly connected to a spark plug.
When the Engine-ECU turns ON the power transistor, the primary current flows through the
ignition coil to ground. When the Engine ECU turns the power transistor “OFF”, the primary
current is cut off and a high voltage is induced into the secondary ignition coil, which causes a
spark in spark plugs when it reaches the ground connection. The Engine-ECU drives the
respective power transistor independently following the firing order 1-3-4-2 in case of a 4-
cylinder engine.
The ignition timing is factory pre-set into the Engine-ECU, which varies it according to en-
gine driving operation. Timing compensations are made according to the pre-set values de-
pending on conditions such as engine coolant temperature, battery voltage, crankshaft and
camshaft position, pressure, etc., to establish the optimum ignition timing.
<System Configuration Diagram>
Fig. 3-12
MMMTC VER 1 3 - 8
3. MPI SYSTEM
(1) Ignition Power Control
Based on the crank angle sensor signal and camshaft position sensor signals, the Engine-
ECU determines the ignition cylinder, calculates the ignition timing and connects/
disconnects, in the firing order, the ignition coil primary current signal to the power transistor
of each cylinder.
Fig. 3-13
(2) Ignition Timing Control
It is believed that the heat energy released by combustion in a cylinder can be converted
most efficiently into engine output when the combustion pressure peaks at about 6-12 degree
ATDC. And it is said that a required period time from the ignition spark to combustion start will
be almost constant regardless of the engine speed. So the corresponding crank angle in-
creases as engine speed increase, therefore, an increase in engine speed requires an igni-
tion advance angle increase.
Further, the combustion velocity depends on engine operating conditions. When the com-
bustion velocity is low (for example, when the engine is lightly loaded), it is necessary to ad-
vance the ignition timing, and when the combustion velocity is high it is necessary to retard
the ignition timing.
[During start]
Engine-ECU initiates ignition at fixed ignition timing of 5° BTDC based on crank angle sen-
sor signal.
[During normal operation]
After determining the basic spark-advance based on the intake air volume and engine
speed, the Engine-ECU makes compensations based on inputs from various sensors to
control the optimum ignition timing.
[Control for checking ignition timing]
M.U.T.-III actuator test function fixes the basic ignition timing to 5° BTDC based on crank
angle sensor signal.
3 - 9 MMMTC VER 1
3. MPI SYSTEM
<List of Main Compensations for Ignition Timing Control>
Compensations Content
Intake air temperature Compensation is made according to intake air temperature. The
compensation higher the intake air temperature the greater the delay in ignition
timing.
Engine coolant tempera- Compensation is made according to engine coolant temperature.
ture compensation The lower the engine coolant temperature the greater the advance
in ignition timing.
Knocking compensation Compensation is made according to the generation of knocking.
The greater the knocking the greater the delay in ignition timing.
Stable idle compensation Compensation is made according to change in idle speed. In case
engine speed becomes lower than target speed, ignition timing is
advanced.
Delay compensation During A/T gear shift, sparking is delayed as compared to normal
when A/T shifting ignition timing to reduce engine output torque and absorb the
shock of the shift change.
Battery voltage compen- Compensation is made depending on battery voltage. The lower
sation the battery voltage the greater the current carrying time and when
battery voltage is high current carrying time is shortened.
(3) Excitation Time Control
The Engine- ECU controls the excitation timing of
the primary coil in order to produce 30 kV or higher
with the secondary coil. The primary current in-
creases at the start of excitation to the coil as
shown in Fig. 3-14. The induced high voltage in the
secondary coil depends on the magnitude of the
primary current when the primary coil current is
shut off.
Fig. 3-14
The Engine-ECU controls the time of interruption to
maintain the primary current at an adequate level.
Retarded amount (4) Knocking Control
The knocking control detects engine knocking
which may occur during a high engine load opera-
tion, and adjusts the ignition timing for optimization
to prevent knocking and protect the engine.
The Engine-ECU judges the necessity of the igni-
tion timing retard according to the knocking level
Fig. 3-15 detected by the detonation sensor. The knocking
compensation is carried out, and a retard amount
corresponding to the knock magnitude is added to
the knock retard compensation until knocking
stops.
When knocking stops, the ignition timing is gradu-
ally advanced at intervals of a predetermined time
until normal advance is restored.
MMMTC VER 1 3 - 10
3. MPI SYSTEM
3. THROTTLE VALVE OPENING ANGLE CONTROL AND IDLE SPEED CONTROL
The electronically controlled throttle valve system electronically regulates the throttle valve
opening. The Engine-ECU monitors the amount of the accelerator pedal travel through the
accelerator pedal position sensor and issues pre-mapped target throttle valve opening val-
ues to the throttle valve control servo unit in accordance with the operating conditions. The
Engine-ECU achieves the target throttle valve opening by pulsing the current supplied to the
throttle valve control servo, which is attached to the throttle body. This system also controls
the idle speed in addition to controlling the throttle valve opening.
Fig. 3-16
[While starting]
The Engine-ECU adds various compensations to the target opening angle that are set
based on the engine coolant temperature, so that the air volume is optimum for starting.
[While idling]
The Engine-ECU controls the throttle valve to achieve the target opening angle that are set
based on the engine coolant temperature. In this way best idle operation is achieved when
the engine is cold and when it is hot. Also, the compensations found in the table of next
page ensure optimum control.
[While driving]
Compensations are made to the target opening angle set according to the accelerator pedal
opening angle and engine speed to control the throttle valve opening angle.
3 - 11 MMMTC VER 1
3. MPI SYSTEM
List of main compensations for throttle valve opening angle and idle speed control
Compensations Content
Stable idle compensation In order to stabilize idle speed immediately after start, target opening
(immediately after start) angle is kept big and then gradually reduced. Compensation values are
set based on the engine coolant temperature.
Idle speed feedback compen- In case there is a difference between the target idle speed and actual
sation engine speed, the Engine-ECU compensates the throttle valve opening
angle based on that difference.
Atmospheric pressure com- At high altitudes atmospheric pressure is less and the intake air density
pensation is low. So, the target opening angle is compensated based on atmos-
pheric pressure.
Engine coolant temperature Compensation is made according to the engine coolant temperature.
compensation The lower the engine coolant temperature the greater the throttle valve
opening angle.
Electric load compensation Throttle opening angle is compensated according to electric load. The
greater the electric load, the greater the throttle valve opening angle.
Compensation when shift is When transmission is changed from P or N range to some other range,
in D range <A/T, CVT> throttle valve opening angle is increased to prevent reduction in engine
speed.
Compensation when A/C is Throttle opening angle is compensated according to functioning of A/C
functioning compressor. While A/C compressor is being driven, the throttle valve
opening angle is increased.
Power steering fluid pressure Throttle opening angle is compensated according to power steering
compensation functioning. When power steering oil pressure rises and power steering
pressure fluid switch is ON, the throttle opening angle is increased.
[Initialize control]
After turning OFF the ignition switch, the Engine-ECU drives the throttle valve from fully
closed position to fully open position and records the fully closed/open studied value of the
throttle position sensor (main and sub) output signals. The recorded values are used as
studied value compensation for compensating basic target opening angle for the next en-
gine start.
[Engine protection control]
If racing continues during a vehicle stopped period (no-load period) for more than the speci-
fied time, the Engine-ECU closes the throttle valve and restricts the engine speed to protect
the engine.
MMMTC VER 1 3 - 12
3. MPI SYSTEM
[Alternator Control]
The Engine-ECU prevents change in idle speed due to sudden increase of alternator load.
During engine idle operation, the Engine-ECU controls the duty of conduction between al-
ternator G terminal and ground (G terminal duty is controlled to be the same as ON duty of
the power transistor inside the voltage regulator). If a high-load device like the headlights
are turned ON while the engine is idling, the electrical current increases suddenly. The En-
gine-ECU restricts the sudden increase in alternator output current by allowing Battery cur-
rent to supply the headlamps. At the same time, alternator output current is increased grad-
ually by increasing the alternator G terminal OFF duty until the alternator produces sufficient
current to run the headlights.
Fig. 3-17
3 - 13 MMMTC VER 1
3. MPI SYSTEM
4. MIVEC (Mitsubishi Innovative Valve Timing Electronic Control System)
(1) Continuous Variable Valve Timing MIVEC
MIVEC is the system that controls, continuously and variably, the intake and the exhaust
valve timings, even when the operating cam profiles are not changed. MIVEC allows for the
optimum valve timings to be controlled in accordance with the engine operation, it improves
the idling stability, as well as the output and the torque in all the operation ranges.
<System Configuration Diagram>
Fig. 3-18
◇ The Engine-ECU identifies the engine operational conditions through the output signals
from each sensor.
◇ Based on the assessed information, the Engine-ECU sends the duty signal to the oil
feeder control valve to control the spool valve position.
◇ Changing the spool valve position allows the oil pressure to be divided into the retarded
chamber and the advanced chamber, as well as allows the phases of the inlet camshaft
and the exhaust camshaft to be continuously changed.
MMMTC VER 1 3 - 14
3. MPI SYSTEM
1) Phase Angle Detection
The detected phase angle is calculated using the inlet camshaft position sensor signal and
the exhaust camshaft position sensor signal.
Fig. 3-19
2) Operation Conceptual Diagram
The Engine-ECU controls the camshaft phase angles in order to attain optimal valve timings
that suit the engine load and engine speed.
Initial phase Control direction
Intake side Most retarded angle Advance direction
Exhaust side Most advanced angle Retard direction
Fig. 3-20
3 - 15 MMMTC VER 1
3. MPI SYSTEM
3) MIVEC Control
The MIVEC control has the following four operation modes according the driving condition
correlating with the engine load and the engine speed.
High torque mode (Ex: Retarded, In: Advanced)
◇ The intake valve closing timing is advanced to ensure sufficient intake air volume.
◇ The exhaust valve opening timing is retarded for higher expansion ratio (improved
charging efficiency)
High output mode (Ex: Advanced, In: Retarded)
◇ The intake valve closing is retarded to synchronize the intake air pulsation for larger
amount of intake air introduction.
Stabilized idling mode (Ex: Advanced- Max, In: Retarded- Max)
◇ The valve overlap has been eliminated to stabilize the combustion at idling.
◇ Initial phase of valve timing
High fuel economy mode (Ex: Retarded, In: Advanced)
◇ The valve overlap has been increased in order to reduce pumping loss.
◇ The exhaust valve opening timing is retarded for higher expansion ratio.
In In
Ex
Ex
High torque mode
High output mode
Stabilized idling mode
High fuel economy mode
In In
Ex
Ex
Fig. 3-21
MMMTC VER 1 3 - 16
3. MPI SYSTEM
(2) Valve Timing & Lift Switching MIVEC
This MIVEC system uses a low-speed cam to actuate the intake valve during low engine
speeds, and a high-speed cam to actuate the intake valve during high engine speeds. As a
result, this system realizes further improvement in low-speed torque and high-speed power
output over the conventional engine.
<System Configuration Diagram>
Fig. 3-22
<Operation>
The low-speed cam has a shorter valve overlap and valve-opening duration, and possesses
characteristics that are well-suited to low-speed operations in which the intake air inertia is
small. The high-speed cam has a longer valve overlap and valve-opening duration, and
possesses characteristics that are well-suited to high-speed operations in which the intake
air inertia is large.
Fig. 3-23
When the engine is operating at low speeds, the oil control valve is OFF (duty cycle ratio:
0%). Therefore, the cam switching control piston remains down, allowing the intake valve to
be actuated by the low-speed cam. As a result, low fuel consumption, low exhaust gas
emissions, and high torque are realized.
When the engine is operating at high speeds, the engine-A/T-ECU turns ON the oil control
valve (duty cycle ratio: 100% for 2 seconds while switching, and 60% after 2 seconds have
elapsed). Consequently, the hydraulic pressure acts on the cam switching control piston,
causing the high-speed cam to actuate the intake valve. As a result, the valve opening dura-
tion and the valve lift increase, effectively increasing the intake air volume and the power
output.
3 - 17 MMMTC VER 1
3. MPI SYSTEM
Under the conditions indicated below, the low-speed cam always operates the intake valve:
◇ Engine coolant temperature below 20°C
◇ Within 10 seconds upon starting the engine
The engine speeds for when the operation of cam switching is carried out are shown in the
table below.
Engine Model Engine speed
Vehicle Model
(Total displacement; mL) at cam switching (r/min)
NA4W 4G69 (2,378) 3,600
CU5W 4G69 (2,378) 4,300
DJ1A 4G69 (2,378) 3,500
DK2A 4G69 (2,378) 4,000
DK4A 6G75 (3,828) 4,000
V87/97W 6G75 (3,828) 3,000
CW6W 6B31 (2,998) 4,750
MMMTC VER 1 3 - 18
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