signal MITSUBISHI MONTERO 1991 Owner's Manual

Press "3" key or press down arrow to display CONFIGURE option
and press ENTER. Configure allows user to customize DRB-II display.
For example, If metric system is more useful, select METRIC from the
menu. All selections in CONFIGURE option remain active until user
changes selection.
SELECT VEHICLE
1) This allows the user to enter information about vehicle
being tested. Usually, this option has more than one display screen.
Use ENTER key to enter vehicle information.
2) When all information about vehicle is entered, DRB-II will
display an information summary the technician has entered. DRB-II will
show an additional option marked CONFIRM. If information is correct,
press CONFIRM. DRB-II will display MAIN MENU.
MAIN MENU
The MAIN MENU represents all diagnostic functions available.
Functions are SYSTEM TESTS, READ FAULTS, STATE DISPLAYS, ACTUATOR
TESTS and ADJUSTMENTS. SYSTEM TESTS is NOT available.
READ FAULTS
This allows technician to read fault codes stored in ECU
memory.
STATE DISPLAYS
1) This allows technician to view conditions at signal level.
The 2 types of signals are analog and digital. Analog signals are
monitored at pins corresponding to vehicle harness splices (e.g. fuel
pump relay).
2) Digital signals correspond to data transmitted by the
system controllers. Both signals are displayed in common units (e.g.
temperature). Use up and down arrow keys on DRB-II to scroll through
displays available.
3) The following ENGINE state displays are available on DRB-
II:
* Module Information - This mode allows technician to read ECU
part number and application.
* Engine Sensors - This mode allows technician to look at
various engine sensors during engine operation.
* Inputs/Outputs - This mode allows technician to read input
and output states of various switches and sensors.
* Custom Display - This screen allows technician to set up
his/her own custom display. Two custom display screens can be
programmed into DRB-II.
* Minimum/Current/Maximum - The MIN/CURRENT/MAX display shows a
history of conditions for a specific sensor. When this option
is selected, maximum, current (static) and minimum values can\
be displayed for a specific sensor. To reset sensors to a
zero value, simply press ENTER key. This display may be used
to isolate intermittent faults. The MIN/CURRENT/MAX display
allows technician to observe operation of 6 different sensor
values. Information is displayed as a 3-digit number. The
first value displayed is the minimum reading, the second
number is the current reading and third valve is the maximum
reading. Typically sensors range between 2-252. Values less
than 2 or greater than 252 will usually indicate that a

Fig. 4: 18-Way ECU Connector
Courtesy of Chrysler Motors.
Fig. 5: 24-Way ECU Connector
Courtesy of Chrysler Motors.
Fig. 6: Self-Diagnostic Connector Terminal Identification
Courtesy of Mitsubishi Motor Sales of America.
FAULT CODES
FAULT CODES TABLE








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Fault Code System Fault Description
11 .................... Open or short in O2 sensor circuit
12 ............... Open or short in airflow sensor circuit
13 ...... Open or short in intake air temp. sensor circuit
14 .......................... Open or short in TPS circuit
15 (1) .... Open or short in motor position sensor circuit
21 ......... Open or short in coolant temp. sensor circuit
22 ........ No voltage change in crank angle sensor signal
23 ............... No voltage change in TDC sensor circuit
24 ( 2) .. No voltage change in vehicle speed sensor signal
25 ........... Open or short in barometric pressure sensor
31 ( 3) ........ Open or short in detonation sensor circuit
41 ..................... Open or short in injector circuit
42 .............. Open or short in fuel pump drive circuit
43 ( 4) ......... Open or short in EGR temp. sensor circuit

\003
E - T H EO RY/O PER ATIO N - E FI

1 991 M it s u bis h i M onte ro
1990-91 ENGINE PERFORMANCE
Chrysler/Mitsubishi Theory & Operation - Fuel Injection
All Models
INTRODUCTION
This article covers basic description and operation of engine
performance-related systems and components. Read this article before
diagnosing vehicles or systems with which you are not completely
familiar.
AIR INDUCTION SYSTEM
NON-TURBOCHARGED ENGINES
All Chrysler/Mitsubishi engines with Port Fuel Injection
(PFI), called Multi-Point Injection (MPI) by the manufacturer, use t\
he
same basic air induction system. Remote air filter (with airflow
sensor) is ducted to a plenum-mounted throttle body.
TURBOCHARGED ENGINES
In addition to basic air induction system used on all other
models, turbocharging system components include turbocharger, air-to-
air intercooler, air by-pass valve, wastegate actuator, wastegate
control solenoid valve and intake ducting.
Wastegate Control Solenoid Valve
Engine Control Unit (ECU) energizes solenoid valve,
controlling leakage rate of turbocharger pressure to wastegate
actuator.
COMPUTERIZED ENGINE CONTROLS
Multi-Point Injection (MPI) is a computerized engine control
system which controls fuel injection, ignition timing, idle speed and
emission control systems.
ELECTRONIC CONTROL UNIT (ECU)
NOTE: Components are grouped into 2 categories. The first category
covers INPUT DEVICES, which control or produce voltage
signals monitored by the Engine Control Unit (ECU). The
second category covers OUTPUT SIGNALS, which are components
controlled by the ECU.
ECU receives and processes signals from input devices. Such
operating conditions as cold starting, altitude, acceleration and
deceleration affect input device signals. Based upon signals received,
ECU sends signals to various components which control fuel injection,
ignition timing, idle speed and emission control systems.
INPUT DEVICES
Vehicles are equipped with different combinations of input
devices. Not all input devices are used on all models. To determine

input device usage on specific models, see appropriate wiring diagram
in M - WIRING DIAGRAMS.
Air Conditioner Switch
When A/C is turned on, signal is sent to ECU. With engine at
idle, ECU increases idle speed through Idle Speed Control (ISC) motor.\
Airflow Sensor
Incorporated in airflow sensor assembly, airflow sensor is a
Karmen Vortex-type sensor which measures intake airflow rate.
Intake air flows through tunnel in airflow sensor assembly.
Airflow sensor transmits radio frequency signals across direction of
incoming airflow, downstream of vortex. Intake air encounters vortex,
causing turbulence in tunnel.
Turbulence disrupts radio frequency, causing variations in
transmission. Airflow sensor converts frequency transmitted into a
proportionate electrical signal which is sent to ECU.
Airflow Sensor Assembly
Mounted inside air cleaner, incorporates airflow sensor,
atmospheric pressure sensor and intake air temperature sensor.
Atmospheric (Barometric) Pressure Sensor
Incorporated in the airflow sensor assembly, converts
atmospheric pressure to electrical signal which is sent to ECU. ECU
adjusts air/fuel ratio and ignition timing according to altitude.
Coolant Temperature Sensor
Converts coolant temperature to electrical signal for use by
ECU. ECU uses coolant temperature information for controlling fuel
enrichment when engine is cold.
Crankshaft Angle & TDC Sensor Assembly
Assembly is located in distributor on SOHC engines. On DOHC
engines, which use Direct (or Distributorless) Ignition System (DIS)\
,
assembly is separate unit mounted in place of distributor. Assembly
consists of triggering disc (mounted on shaft) and stationary optical
sensing unit. Camshaft drives shaft, triggering optical sensing unit.
ECU determines crank angle and TDC based on signals received from
optical sensing unit.
Detonation Sensor (Turbo Only)
Located in cylinder block, senses engine vibration during
detonation (knock). Sensor converts vibration into electrical signal.
ECU retards ignition timing based on this signal.
Engine Speed (Tach Signal)
ECU uses ignition coil tach signal to determine engine speed.
Idle Position Switch
On all DOHC engines and Sigma 3.0L, idle position switch is
separate switch mounted on throttle body. On all other models, idle
position switch is incorporated in ISC motor or throttle position
sensor, depending on vehicle application. When throttle valve is
closed, switch is activated. When throttle valve is at any other
position, switch is deactivated. This input from idle position switch
is used by ECU for controlling fuel delivery time during deceleration.
Ignition Timing Adjustment Terminal
Used for adjusting base ignition timing. When terminal is
grounded, ECU timing control function is by-passed, allowing base
timing to be adjusted.

Inhibitor Switch (Automatic Transmission Only)
Inhibitor switch senses position of transmission select
lever, indicating engine load due to automatic transmission
engagement. Based on this signal, ECU commands ISC motor to increase
throttle angle, maintaining optimum idle speed.
Intake Air Temperature Sensor
Incorporated in airflow sensor assembly, this resistor-based
sensor measures temperature of incoming air and supplies air density
information to ECU.
Motor Position Sensor (MPS)
Incorporated in ISC motor (or separate unit on some models),
senses ISC motor plunger position and sends electrical signal to ECU.
Oxygen (O2) Sensor
Located in exhaust system, generates an output voltage.
Output voltage varies with oxygen content of exhaust gas stream. ECU
adjusts air/fuel mixture based on signals from oxygen sensor.
Power Steering Oil Pressure Switch
Detects increase in power steering oil pressure. When power
steering oil pressure increases, switch contacts close, signalling
ECU. ECU commands ISC motor, raising idle speed to compensate for drop
in engine RPM due to power steering load.
TDC Sensor
See CRANKSHAFT ANGLE & TDC SENSOR ASSEMBLY.
Throttle Position Sensor (TPS)
A variable resistor mounted on throttle body. ECU uses
voltage signal received from TPS to determine throttle plate angle.
Vehicle Speed Sensor
Located in speedometer in instrument cluster, uses a reed
switch to sense speedometer gear revolutions. ECU uses gear
revolutions to determine vehicle speed.
OUTPUT SIGNALS
NOTE: Vehicles are equipped with different combinations of
computer-controlled components. Not all components listed
below are used on every vehicle. For theory and operation on
each output component, refer to the system indicated in
brackets after component.
CHECK ENGINE Light
See SELF DIAGNOSTIC SYSTEM.
EGR Control Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) CONTROL under EMISSION
SYSTEMS.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pressure Control Solenoid Valve (Turbo Only)
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pressure Regulator
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump Relay (MPI Control Relay)

See FUEL DELIVERY under FUEL SYSTEM.
Idle Speed Control Servo
See IDLE SPEED under FUEL SYSTEM.
Power Transistor(s) & Ignition Coils
See IGNITION SYSTEMS.
Purge Control Solenoid Valve
See EVAPORATIVE CONTROL under EMISSION SYSTEMS.
Self-Diagnostic Connector
See SELF-DIAGNOSTIC SYSTEM.
Wastegate Control Solenoid Valve
See TURBOCHARGED ENGINES under AIR INDUCTION SYSTEM.
FUEL SYSTEM
FUEL DELIVERY
Electric fuel pump (located in gas tank) feeds fuel through
in-tank fuel filter, external fuel filter (located in engine
compartment) and fuel injector rail.
Fuel Pump
Consists of an impeller driven by a motor. Pump has an
internal check valve to maintain system pressure and a relief valve to
protect the fuel pressure circuit. Pump receives voltage supply from
Multi-Point Injection (MPI) control relay.
Fuel Pressure Control Solenoid Valve (Turbo Only)
Prevents rough idle due to fuel percolation. On engine
restart, if engine coolant or intake air temperatures reach a preset
value, ECU applies voltage to fuel pressure control solenoid valve for
2 minutes after engine re-start. Valve opens, allowing atmospheric
pressure to be applied to fuel pressure regulator diaphragm. This
allows maximum available fuel pressure at injectors, enriching fuel
mixture and maintaining stable idle at high engine temperatures.
Fuel Pressure Regulator
Located on fuel injector rail, this diaphragm-operated relief
valve adjusts fuel pressure according to engine manifold vacuum.
As engine manifold vacuum increases (closed throttle), fuel
pressure regulator diaphragm opens relief valve, allowing pressure to
bleed off through fuel return line, reducing fuel pressure.
As engine manifold vacuum decreases (open throttle), fuel
pressure regulator diaphragm closes valve, preventing pressure from
bleeding off through fuel return line, increasing fuel pressure.
FUEL CONTROL
Fuel Injectors
Fuel is supplied to engine through electronically pulsed
(timed) injector valves located on fuel rail(s). ECU controls amount\
of fuel metered through injectors based upon information received from
sensors.
IDLE SPEED
Air Conditioner Relay
When A/C is turned on with engine at idle, ECU signals ISC

motor to increase idle speed. To prevent A/C compressor from switching
on before idle speed has increased, ECU momentarily opens A/C relay
circuit.
Idle Speed Control (ISC) Motor
Controls pintle-type air valve (DOHC engines) or throttle
plate angle (SOHC engines) to regulate volume of intake air at idle.
During start mode, ECU controls idle intake air volume
according to coolant temperature input. After starting, with idle
position switch activated (throttle closed), fast idle speed is
controlled by ISC motor and fast idle air control valve (if equipped).\
When idle switch is deactivated (throttle open), ISC motor
moves to a preset position in accordance with coolant temperature
input.
When automatic transmission (if equipped) is shifted from
Neutral to Drive, A/C is turned on or power steering pressure reaches
a preset value, ECU signals ISC motor to increase engine RPM.
Fast Idle Air Control Valve
Some models use a coolant temperature-sensitive fast idle air
control valve, located on throttle body, to admit additional intake
air volume during engine warm-up. Control valve closes as temperature
increases, restricting by-pass airflow rate. At engine warm-up, valve
closes completely.
IGNITION SYSTEMS
DIRECT IGNITION SYSTEM (DIS) - DOHC ENGINES
Ignition system is a 2-coil, distributorless ignition system.
Crankshaft angle and TDC sensor assembly, mounted in place of
distributor, are optically controlled.
Power Transistors & Ignition Coils
Based on crankshaft angle and TDC sensor inputs, ECU controls
timing and directly activates each power transistor to fire coils.
Power transistor "A" controls primary current of ignition coil "A" to
fire spark plugs on cylinders No. 1 and 4 at the same time. Power
transistor "B" controls primary current of ignition coil "B" to fire
spark plugs on cylinders No. 2 and 3 at the same time.
Although each coil fires 2 plugs at the same time, ignition
takes place in only one cylinder since the other cylinder is on its
exhaust stroke when plug fires.
ELECTRONIC IGNITION SYSTEM - SOHC ENGINES
Mitsubishi breakerless electronic ignition system uses a disc
and optical sensing unit to trigger power transistor.
Power Transistor & Ignition Coil
Power transistor is mounted inside distributor with disc and
optical sensing unit. When ignition is on, ignition coil primary
circuit is energized. As distributor shaft rotates, disc rotates,
triggering optical sensing unit. ECU receives signals from optical
sensing unit. Signals are converted and sent to power transistor,
interrupting primary current flow and inducing secondary voltage.
IGNITION TIMING CONTROL SYSTEM
Ignition timing is controlled by ECU. ECU adjusts timing
based upon various conditions, such as engine temperature, altitude
and detonation (turbo vehicles only).

EMISSION SYSTEMS
EXHAUST GAS RECIRCULATION (EGR) CONTROL
Federal (Non-Turbocharged)
To lower oxides of nitrogen (NOx) exhaust emissions, a non-
computer controlled exhaust gas recirculation system is used. EGR
operation is controlled by throttle body ported vacuum. Vacuum is
routed through thermovalve to prevent EGR operation at low engine
temperatures.
Spring pressure holds EGR valve closed during low vacuum
conditions (engine idling or wide open throttle). When vacuum pressure\
increases and overcomes EGR spring pressure, EGR valve is lifted and
allows exhaust gases to flow into intake manifold for combustion.
California & Turbocharged
ECU controls EGR operation by activating EGR control solenoid
valve according to engine load. When engine is cold, ECU signals EGR
control solenoid valve to deactivate EGR.
California models are equipped with an EGR temperature
sensor. When EGR malfunction occurs, EGR temperature decreases and ECU
illuminates CHECK ENGINE (malfunction indicator) light.
EGR Control Solenoid Valve
Denies or allows vacuum supply to EGR valve, based upon ECU
commands.
Thermovalve
Denies or allows vacuum supply to EGR valve based on coolant
temperature.
EVAPORATIVE CONTROL
Fuel evaporation system prevents fuel vapor from entering
atmosphere. System consists of a special fuel tank with vapor
separator tanks (if equipped), vacuum relief filler cap, overfill
limiter (2-way valve), fuel check valve, thermovalve (if equipped),
charcoal canister, purge control valve, purge control solenoid valve
and connecting lines and hoses.
Purge Control Solenoid Valve
When engine is off, fuel vapors are vented into charcoal
canister. When engine is warmed to normal operating temperature and
running above idle, ECU energizes purge control solenoid valve,
allowing vacuum to purge valve.
Canister vapors are then drawn through purge valve into
intake manifold for burning. Purge control solenoid valve remains
closed during idle and engine warm-up to reduce HC and CO emissions.
HIGH ALTITUDE CONTROL (HAC)
This system compensates for variations in altitude. When
atmospheric (barometric) pressure sensor determines vehicle is above
preset altitude, ECU compensates by adjusting air/fuel mixture and
ignition timing. If HAC system is inoperative, there will be an
increase in emissions.
PCV VALVE
Positive Crankcase Ventilation (PCV) valve operates in the
closed crankcase ventilation system. Closed crankcase ventilation

system consists of PCV valve, oil separator, breather and ventilation
hoses.
PCV valve is a one-way check valve, located in valve cover.
When engine is running, manifold vacuum pulls PCV valve open, allowing
crankcase fumes to enter intake manifold. If engine backfires through
intake manifold, PCV valve closes to prevent crankcase combustion.
SELF-DIAGNOSTIC SYSTEM
Self-diagnostic system monitors input and output signals. On
all models, codes can be read using analog voltmeter. On some models,
scan tool can be used to read codes. For additional information, see G
- TESTS W/ CODES article.
CHECK ENGINE Light
Also called Malfunction Indicator Light by manufacturer,
comes on when ignition is turned on. Light remains on for several
seconds after engine has started. If an abnormal input signal occurs,
light comes on and code is stored in memory. If an abnormal input
signal returns to normal, ECU turns light off but code remains stored
in memory until cleared. If ignition is turned on again, light will
not come on until ECU detects malfunction during system operation.
NOTE: ECU diagnostic memory is retained by direct power supply
from the battery. Memory is not erased by turning off
ignition but is erased if battery or ECU is disconnected.

Low fuel pressure Test pressure regul-
ator and fuel pump,
check for restricted
lines and filters
No distributor reference Repair ignition
pulses system as necessary
Open coolant temperature Test sensor and
sensor circuit wiring
Shorted W.O.T. switch in Disconnect W.O.T.
T.P.S. switch, engine
should start
Defective ECM Replace ECM
Fuel tank residual pressure Test for fuel
valve leaks pressure drop after
shut down









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Hard Starting Disconnected hot air tube Reconnect tube and
to air cleaner test control valve
Defective Idle Air Control Test valve operation
(IAC) valve and circuit
Shorted, open or misadjusted Test and adjust or
T.P.S. replace T.P.S.
EGR valve open Test EGR valve and
control circuit
Poor Oxygen sensor signal Test for shorted or
circuit
Incorrect mixture from PCV Test PCV for flow,
system check sealing of oil
filter cap









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Poor High Speed Low fuel pump volume Faulty pump or
Operation restricted fuel
lines or filters
Poor MAP sensor signal Test MAP sensor,
vacuum hose and
wiring
Poor Oxygen sensor signal Test for shorted or
open sensor or
circuit
Open coolant temperature Test sensor and
sensor circuit wiring
Faulty ignition operation Check wires for
cracks or poor con-
nections, test
secondary voltage
with oscilloscope
Contaminated fuel Test fuel for water