Mitsubishi Montero (1991+). Manual - part 286

voltage or resistance values using a DVOM while attempting to

reproduce conditions which may cause intermittent fault. A status

change on DVOM indicates a fault has been located.

         When using a DVOM to pinpoint faults, monitor voltage reading

with ignition on, or vehicle running. Ensure ignition is in OFF

position or negative battery cable is disconnected when monitoring

circuit resistance. Change in ohmmeter reading during test procedures

indicates area of fault.

         TEST PROCEDURES

         Intermittent Simulation

         To reproduce conditions which cause intermittent fault, use

the following methods:

      *  Lightly vibrate component.

      *  Heat component.

      *  Wiggle or bend wiring harness.

      *  Spray component with water.

      *  Remove/apply vacuum source.

         Monitor circuit/component voltage or resistance while

simulating intermittent fault conditions. If vehicle is running,

monitor for self-diagnostic codes. Use test results to identify a

faulty component or circuit.

E - THEORY/OPERATION - EFI 



1991 Mitsubishi Montero

         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 the

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)