engine MITSUBISHI ECLIPSE 1990 Repair Manual

FUEL SYSTEM -Fuel Supply and Fuel Pressure Control
FUEL-PRESSURE CONTROL VALVE
14-11To fuel
-
Fuel-pressureregulatorFuel-pressurecontrol valve
Intake-airEnginecontrol
unit
Usually, the negative pressure (vacuum) of the
intake manifold is applied to the fuel-pressure
regulator, and, because the fuel pressure is thus
held at a fixed constant level relative to the pressure
within the intake manifold, the amount to fuel
injected is regulated so as to be proportional to the
injectors’ actuation time. If, however, the engine
coolant-temperature and the intake air temperature
are high when then engine is started, the engine
control unit sends a flow of current to the fuel-
pressure control valve, with the result that outside
air (atmospheric) pressure acts upon the fuel-
pressure regulator.
0Fuel ump
1chec terminal 1!Fuel pumpAs a result. the
fuel pressure is increased and the
generation of fuel vapors caused by high tem-
perature is suppressed, thereby maintaining idling
stability immediately after restarting under
high-temperature conditions.
Note that there is a return to the usual fuel pressure
level after two minutes or more have passed after
starting is completed.
In addition, the circuitry of the fuel-pressure control
valve. is interrupted, thus controlling so that the fuel
pressure corresponds to supercharging pressure,
under high-load driving conditions (during super-
charged driving by the turbocharger).
FU,EL PUMP CHECK TERMINAL
This terminal is for directly driving the fuel pump.
By applying the battery voltage directly to this terminal, you can
check fuel pump operation or check fuel leaks from the
fuel
line.
__. - ---

140’I2FUEL SYSTEM- Intake Air Control
INTAKE AIR CONTROL
GENERAL DESCRIPTION
Rl4oA?, Speed adjusting screwIdle oositionswitch-
Throttle valve
0
+ Bypass air flow
before metenng
Q Bypass air fjow
Iafter metenng
Idle soeed control servo
-?hrottle position sensor
Fast idle air valve
oolant from thermostat case
ITo return pipe6FUO777Control of the volume of intake air is performed by the throttle
valve, the speed adjusting screw, the fast idle air valve and the
idle speed control servo, all of which are mounted on
ttithrottle body.
iControl by idle
w/d c;zk;;fast
hhidle air valve
Speed adjusting screwThrottle valve
m-30~22) of321 sofm 6of140~ 901164
Coolant temperature ‘C (OF)6Fuo!DURING ENGINE WARM UP
The intake air flow during fast idle is controlled by both the wax
actuated air valve which functions. in response to the engine
coolant temperature and the idle speed control servo that is
controlled by the engine control unit.
AFTER ENGINE HAS BEEN WARMED UP
Control of the intake air flow during curb idle (or the control of
curb idle speed) is performed by the idle speed control servo
which in turn is controlled by the engine control unit.
Refer to page 1445 for control of the idle speed control servo.The idle speed can be adjusted. by increasing or decreasing theintake air flow rate with the speed adjusting screw.
The off-idle intake air flow is controlled by the throttle
valve;operation of the accelerator pedal determines the degree that
the throttle valve is open at any particular moment.
-
.?‘h,
. .

FUEL SYSTEM- Intake Air Control
SPECIFICATIONS
ternsThrottle body
Throttle bore diametermm
(in.1Fast idle air valve
TwValve closing temperature
“C (“F)
Idle speed control servo
TypeSpecifications
60 (2.362)
WAX type
Approximately 50
(122)Stepper motor type
FAST IDLE AIR VALVEEngine coolant
LAir valve
Waxpellet
Valve seat
6FUO642The fast idle air valve is a wax actuated valve. The
engine coolant circulates around the wax pellet.
causing the air valve to be forced out as the coolant
temperature increases, thus decreasing the bypassair flow rate. The valve is closed completely when
the coolant temperature is approximately 50°C
(122°F) or higher.

14-14
.._~- ---.FUEL SYSTEM
- Sensors
SENSORSRlUGENERAL DESCRIPTION
The types and functions of the sensors are as listedsend corresponding signals to the engine control
below. These sensors detect engine conditions and
unit.
SENSORSFUNCTION
AIR FLOW SENSOR
fSenses the intake arr volume with a Karman vortex flow meter.
INTAKE AIR TEMPERATURE
SENSORSenses the Intake air temperature (temperature of air at
the point of entry into the air cleaner).I
BAROMETRIC PRESSURE
SENSORISenses the barometric pressure faltrtude) wrth a
semiconductor diffusion type pressure sensor.
$;;OOf;T TEMPERATURESenses the engine coolant tern
THROTTLE
POSITISenses the throttle
tI
IDLE POSITION SWITCHSenses whether or not the accelerator pedal is being
operated with a contact switch.
Senses the top dead center on compression stroke of
NO. 1 and No. 4 cylinders with an LED and photo diode pair.
CRANK ANGLE SENSORSenses the crank angle of each cylinder with an LED
and photo diodepair.
T
OXYGEN SENSORSenses
actrvation of the air con
POWER STEERING OIL
PRESSURE SWITCHc-lSenses the power steering ‘load with a contact switch.
IGNITION SWITCHSenses ON/OFF
posrtion of the ignition switch.I
Senses engine cranking.
,
IGNITION TIMING
ADJUSTMENT TERMINALWhen this terminal is shorted, the ignition timing and idle
speed control servo is set in the adjustrng mode by the enginecontrol unit.
INHIBITOR SWITCHSenses the *P” and “N” positthe automatic transaxle.Senses.
by pieto-electric element,. cylinder block
vibrations that occur when there ISengineknocking.
CONTROL RELAY
(Fuel pump drive signal)
lFnorne ianitron sianal!Senses ignrtton coil prIman/ voltage.

FUEL SYSTEM - Sensors
AIR FLOW SENSOR
IAir
0
Power supplyAir flow sensor(from control relay)
r-- Amplifier Few
L+--J Vortex ITo throttle
bodyEngine control unit
>- Power supply
e5 volts
6FUO493
EC1537
Karman vortex
(1) Slow air flow
6FUO423
(2) Fast air flow
6Fuo42rThe air flow sensor for measuring the volume of engine intake
air uses the Karman vortex phenomenon to detect the air flow
rate. The air flow rate detected in this way is sent to the engine
control unit as data on intake air volume.
Using this signal and the engine rpm signal, the engine control
unit makes computations to determine the basic injection
timing.
A barometric pressure sensor and an intake air temperature
sensor are installed on the air flow sensor.
The air flow sensor consists of the following parts:
l Rectifier:
Rectifies the flow of intake air admitted through the air
cleaner.l Vortex generating column:
Serves to generate Karman vortices.
l Transmitter:
Transmits ultrasonic waves.
l Receiver:
Receives ultrasonic waves.
l Amplifier:
Generates ultrasonic waves.
l Modulator:
Converts ultrasonic waves that have been received into
electric pulses.
l Acoustic material
Karman Vortex
When a triangular column is placed in an air stream, regularly
spaced vortices are generated downstream alternately on
either side of the column. These vortices are called
“Karman
vortices”.The number of vortices generated is proportional to a
cloSedegree to the volume of air flow in a given time; the higher the
flow speed, the more vortices are generated.

FUEL SYSTEM - SensorsWhen more air
is drawnT1
Pulses generated by modulatorWhen
less air is drawn6FUO42
TI
IPulses generated by modulator6FuWAs a result, when more air is drawn, the modulator
generates more pulses, and when less air is drawn, it
generates less pulses.
The air flow sensor measures the intake air flow based on
this principle.
INTAKE AIR TEMPERATURE SENSOR
IIntake airtemperature sensor
Intake airAir bypass pipesEC654
Intake airtemperature
sensor
s-v
r .==
II
fi ;=---
Engine control unit
6 FUOOSL-20
I410 (32)20 I6913
Intake air temoerature
Intake air temperature “C (‘Fl 1624581621008
e intake air temperature sensor mounted at theBased on the sensor output voltage. the engine
.
..Jstrated location on the air flow sensor is acontrol unit determines the intake air temperature
thermistor which is a kind of resistor whose and corrects the amount of fuel to be injected
resistance changes as a function of the intake air
accordingly.temperature.Curves indicating the sensor characteristics are
shown above.

14-18FUEL SYSTEM - Sensors
tBAROMETRIC PRESSURE SENSOR
Barometnc rxessure sensor
EC1537
Barometncpressure sensor
Enginecontrol unit
1OFUO576
/
760 (30)Barometric pressure mmHg
(in.Hg)EC1551A barometric pressure sensor is
alas mounted on
the
aif flow sensor. It senses the barometric
pressure and converts it to electrical voltage which
is sent as a signal to the engine control unit.
Using this signal, the engine control unit calculates
the altitude
of.the location where the vehicle is, and
corrects the fuel injection quantity for the optimum
air-fuel ratio at that altitude, and also corrects the
COOLANT TEMPERATURE SENSOR
Terminal 26EL0069ignition timing.
This ensures improved driveability at high altitudes.
The barometric pressure sensor converts the pres-
sure to a voltage making use of the fact that the
resistance of a strain gauge changes in direct
proportion to the pressure as shown in this diagram
which
illustratestherelationship between
barometric pressure and output voltage.
Engine control unit
Coolanttemperature
sensor
-a
Tg-I
h-esI
*
5 volts
LizIdr
tSFUOLSL
L0 (32120 (68)Coolant temperature -The engine coolant temperature sensor installed in
the coolant passage of the thermostat case is a
thermistor whose resistance changes with the
engine coolant temperature.
The
annine control unit iudoes the enoine warm UDstate based on the output voltage of this sensor and
provides optimum mixture enrichment when the
engine is cold.
The sensor characteristics are as shown above..:I

FUEL SYSTEM - Sensors
THROTTLE POSITION SENSOR
ThrottleThrottle
posItIon
sensorposltion sensor
,_Il-
Engine control unit
1
6FU0782
Throttle opening deg.
Full o IO 20 30 4070 0002closeFullopenThe throttle position sensor is a variable resistor
whose movable contact rotates
coaxially with the
cattle valve shaft, thus sensing the throttle valve
.
,,ening.As the throttle valve shaft rotates, the sensor outputgenerates, the engine control unit detects the
throttle valve opening and determines the engine
operation mode (acceleration or deceleration).
The relationship between the throttle opening and
the output voltage is as shown above.
voltage changes. Based on the signal the sensor
IDLE POSITION SWITCH
Idle positionswitchTermtnal
7FUO20Throttle body
Idle positlonswitch
I6Fw497I
rle idle position switch is a contact type switch thatinto the throttle bore when the valve is fully closed.
detects operation of the accelerator pedal. ThisThis setting has been performed accurately at the
switch also serves as the throttle stop screw, whichfactory; the lock nut should not be loosened, or the
has been set at the minimum opening of the throttleidle position switch be moved inadvertently.
‘valve so as to prevent the throttle valve from biting_

FUEL SYSTEM - Sensors
CRANK ANGLE SENSOR
II
DiscSensor
The crank angle sensor is mounted on the cylinder
head and is directly coupled to the intake camshaft.The crank angle sensor consists of a disc -and a
sensor unit.
Mu0499Slit for
crank anglesensor
Photo diode
LED
The disc, made of metal, has four slits located 90 degrees aparton its periphery and two slits located 180 degrees apart inward
of the four slits.
-The inner slits are used by the top dead center sensor
th,detects the top dead center of the No.
1 and No. 4 cylinders,
and the outer four slits are used by the crank angle sensor that
detects the crank angle. The disc is positioned on the sensor
shaft and rotates as a unit with it, being turned by the intake
camshaft.The sensor unit has two
LEDs and two photo diodes, used’to
detect the crank angle sensor slits and the top dead center
sensor slits.
The disc rotates between the
LEDs and the photo diodes. Each
time a slit comes between a LED and photo diode pair, the light
emitted by the LED reaches the photo diode by passing
through the slit.
Sensor unit
I I1
Power supply
I
Engine control untt
r
Crank angleslgnal

FUEL SYSTEM - Sensors14-21When exposed to light, the photo diode conducts
urrent in a direction opposite to an ordinary diode.
.s a result, current flows in the direction indicated
by the arrow and dotted line and a voltage (5 volts) isapplied to the comparator of the sensor unit so that
the terminal voltage of the engine control unit
becomes 5 volts. When the disc rotates further andthe slit moves beyond the space between the
LED/photo diode pair, the light can no longer reach
the photo diode, thus the current indicated by the
dotted line ceases to flow and the terminal voltage
of the engine control unit becomes 0 volt.
tn this
way, pulse signals are sent to the engine control
unit from the sensor unit.
OXYGEN SENSOR
k
1 ~~~~t13ate~ousingCoverLead wiresConnectorHeater
Enginecontrol unit6FUlOO5
- Oxygen‘-serisor
The oxygen sensor is mounted at the outlet of the exhaust
manifold or the turbocharger. The sensor, which uses an
oxygen concentration cell having a, solid electrolyte, has such
characteristics that its output voltage changes sharply in the
vicinity of the stoichiometric air/fuel ratio.
The sensor makes use of this characteristic to detect oxygen
concentration in the exhaust gas and feeds back the signal to
the engine control unit, which then decides if the air/fuel ratio is
rich or iean relative to the stoichiometric ratio.
Based on this decision, the air/fuel ratio is feedback-controlled
to achieve the stoichiometric ratio at which the catalytic
converter operates most effectively.
In addition, because this oxygen sensor incorporates a heater,
the response of the sensor is good even if the temperature of
the exhaust gas is low, and, as a result, feedback control of the
air/fuel ratio is possible for a short time after the engine is
started.
Stoichiometric air/fuel ratlo
r3
Lean
Air/fuel ratioEC1007