Engine Controls - Theory & Operation: Other Mitsubishi Eclipse III

AIR INDUCTION SYSTEM

All models, except Mirage with 1.5L engine, use a Volume Airflow (VAF) sensor. These models use an air induction system using a remote air filter (with VAF sensor) connected to a plenum-mounted throttle body.

Mirage 1.5L uses a Manifold Absolute Pressure (MAP) sensor. Filtered air is ducted to a plenum-mounted throttle body.

COMPUTERIZED ENGINE CONTROLS

Sequential Fuel Injection (SFI) is a computerized engine control system, which controls fuel injection, ignition timing, idle speed and emission control systems. Fuel injectors are pulsed sequentially, in firing order.

ENGINE CONTROL MODULE/POWERTRAIN CONTROL MODULE (ECM/PCM)

Vehicles have either ECM or PCM. Vehicles with manual transmission have ECM. Vehicles with automatic transmission have either ECM with separate Transmission Control Module (TCM), or PCM, depending on model. PCM combines functions of ECM and TCM. ECM/PCM receives and processes signals from input devices. Operating conditions such as cold starting, altitude changes, acceleration and deceleration affect input device signals. Based on signals received, ECM/PCM sends signals to various components which control fuel injection, ignition timing, idle speed and emission control systems. For ECM/PCM location, see ECM/PCM LOCATIONS .

ECM/PCM LOCATIONS

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES , which control or produce voltage signals monitored by ECM/PCM. The second category covers OUTPUT SIGNALS , which are components controlled by ECM/PCM.

INPUT DEVICES

Note. 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 under ENGINE PERFORMANCE in WIRING DIAGRAMS. The following are available input devices.

Air Conditioning Switch

When A/C is turned on, signal is sent to ECM/PCM. With engine at idle, ECM/PCM increases idle speed through Idle Air Control (IAC) motor.

Barometric (BARO) Pressure Sensor

Sensor is incorporated into Volume Air Flow (VAF) sensor assembly, except on Mirage 1.5L. On Mirage 1.5L, barometric pressure is obtained from MAP sensor at key on, engine off. BARO sensor converts barometric pressure to an electrical signal, which is sent to ECM/PCM. ECM/PCM adjusts air/fuel ratio and ignition timing according to altitude.

Camshaft Position (CMP) Sensor

CMP sensor is a Hall-Effect type sensor. ECM/PCM determines cylinder No. 1 TDC based on pulse signals received from CMP sensor. CMP sensor input is used to determine injector triggering sequence. On vehicles with Distributorless Ignition Systems (DIS) CMP sensor input is also used to determine which coil to fire. On engines with distributor, CMP sensor is located in distributor. On engines with DIS, CMP sensor is located at front or rear of engine by camshaft.

Closed Throttle Position Switch

Closed throttle position switch is located inside Throttle Position (TP) sensor. ECM/PCM senses whether accelerator pedal is depressed or not. High voltage (open) or low voltage (closed) signal is input to ECM/PCM, which then controls Idle Air Control (IAC) motor based on input signal.

Crankshaft Position (CKP) Sensor

CKP sensor is located on front of engine by crankshaft. ECM/PCM determines crankshaft position based on pulse signals received from CKP sensor, and then controls MFI timing and ignition timing.

Engine Coolant Temperature (ECT) Sensor

ECT sensor converts coolant temperature to electrical signal for use by ECM/PCM. ECT input is used for fuel injection, idle air and ignition timing control by ECM/PCM. ECM/PCM can not go into closed loop fuel system management until ECT input indicates engine is warm enough.

Fuel Tank Differential Pressure Sensor

A voltage proportional to pressure in the fuel tank is sent from the output terminal of fuel tank differential sensor to the PCM. ECM/PCM monitors performance of Evaporative Emission Control System (EVAP) system using these signals. ECM/PCM uses input from FTDP sensor to monitor EVAP system pressure changes and calculates whether leak exists.

Fuel Level Sensor

The fuel gauge drive signal is input to PCM. ECM/PCM monitors this sensor in case of open or short circuit malfunction.

Fuel Temperature Sensor

The fuel temperature sensor converts fuel temperature to a voltage. ECM/PCM detects the fuel temperature in the fuel tank with this voltage. ECM/PCM monitors this sensor in case of open or short circuit malfunction.

Heated Oxygen Sensor (HO2S)

HO2S detects oxygen content in exhaust gas and sends this information to ECM/PCM. ECM/PCM uses input signals from front HO2S to control air-fuel mixture by varying duration of fuel injection. ECM/PCM compares signals from rear HO2S to signals from front HO2S to monitor catalytic converter performance. HO2S heater speeds heating of HO2S which speeds up entry into closed loop operation. HO2S heater also stabilizes sensor temperature regardless of exhaust gas temperature to allow for more accurate exhaust oxygen content readings.

Intake Air Temperature (IAT) Sensor

On engines using Volume Air Flow (VAF), IAT sensor is incorporated into VAF Sensor assembly. On engines using Manifold Absolute Pressure (MAP) sensor, IAT sensor is located in intake plenum. This resistor-based sensor measures temperature of incoming air and sends it to ECM/PCM. Depending on configuration, IAT input may be used for fuel injection, idle air, and/or ignition timing control.

Knock Sensor (KS)

KS is located in cylinder block and senses engine vibration during detonation (knock). KS converts vibration into electrical signal. ECM/PCM retards ignition timing based on this signal.

Manifold Differential Pressure (MDP) Sensor

MDP sensor converts negative air pressure in intake manifold plenum into voltage signals sent to ECM/PCM. ECM/PCM monitors performance of Exhaust Gas Recirculation (EGR) system using these signals.

Park/Neutral Position (PNP) Switch (Automatic Transmission)

PNP switch senses position of transmission select lever, indicating engine load due to automatic transmission engagement. Based on this signal, ECM/PCM commands IAC motor to increase throttle angle, maintaining optimum idle speed.

Power Steering Oil Pressure Switch

Switch detects increase in power steering oil pressure. When power steering oil pressure increases, switch contacts close, signaling ECM/PCM. ECM/PCM commands IAC motor, raising idle speed to compensate for drop in engine RPM due to power steering load.

Throttle Position (TP) Sensor

TP sensor is a variable resistor mounted on throttle body. ECM/PCM uses voltage signal from TP sensor to determine throttle plate angle. TP sensor input is used for fuel injection control and idle air control.

Vehicle Speed Sensor (VSS)

Mounted on transmission, VSS sends a pulsing signal to ECM/PCM for vehicle speed calculation. ECM/PCM uses this calculation for cruise control and fuel cut-off.

Volume Airflow (VAF) Sensor

VAF sensor is located in air intake system behind air cleaner. VAF sensor is a vortex type sensor that sends frequency signal to ECM/PCM. ECM/PCM uses signal to calculate intake air flow rate and adjust air/fuel ratio by controlling fuel injector duration.

OUTPUT SIGNALS

Note. Vehicles are equipped with various combinations of computer-controlled components. Not all components listed below are used on every vehicle. To determine component usage on specific models, see appropriate wiring diagram under ENGINE PERFORMANCE in WIRING DIAGRAMS. For theory and operation on each output component, refer to system indicated after component.

A/C Compressor Clutch Relay Control

See AIR CONDITIONING (A/C) RELAY .

Data Link Connector (DLC)

See SELF-DIAGNOSTIC SYSTEM .

EGR Solenoid

See EXHAUST GAS RECIRCULATION (EGR) CONTROL .

Fuel Injectors

See FUEL INJECTORS under FUEL CONTROL in FUEL SYSTEM.

Fuel Pump Relay Control

See FUEL PUMP RELAY CONTROL .

Idle Air Control (IAC) Motor

See IDLE AIR CONTROL (IAC) MOTOR under IDLE SPEED in FUEL SYSTEM.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT (MIL) under SELF-DIAGNOSTIC SYSTEM.

Power Transistor(s) & Ignition Coils

See IGNITION SYSTEMS .

Purge Solenoid Valve

See PURGE SOLENOID VALVE under EVAPORATIVE CONTROL under EMISSION SYSTEMS.

Vent Solenoid Valve

See VENT SOLENOID VALVE under EVAPORATIVE CONTROL under EMISSION SYSTEMS.

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

Fuel pump consists of a motor-driven impeller. Pump has an internal check valve to maintain system pressure, and a relief valve to protect fuel pressure circuit. Pump receives voltage supply from MFI control relay.

ECM/PCM turns fuel pump relay ON so that current is supplied to the fuel pump while engine is cranking or running.

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 is supplied to engine through sequentially electronically pulsed (timed) injectors located on fuel rail(s). ECM/PCM controls amount of fuel metered through injectors (injector on-time) based on information received from sensors.

Air Conditioning (A/C) Relay

When A/C is turned on with engine at idle, ECM/PCM signals IAC motor to increase idle speed. To prevent A/C compressor from switching on before idle speed has increased, ECM/PCM momentarily opens A/C relay circuit.

Stepper motor controls pintle-type air valve to regulate volume of intake air at idle.

During start mode, ECM/PCM controls idle intake air volume according to Engine Coolant Temperature (ECT) sensor input. After starting, with when throttle is in idle position, idle speed is controlled by IAC motor.

When throttle is opened, IAC motor moves to a preset position in accordance with ECT sensor input.

ECM/PCM signals IAC motor to increase engine RPM in following situations: A/T (if applicable) is shifted from Neutral to Drive, A/C is turned on, or power steering pressure reaches a preset value.

DIRECT IGNITION SYSTEM (DIS)

Depending on number of cylinders, ignition system is a 2-coil or 3-coil, distributorless ignition system. ECM/PCM controls timing and directly activates each power transistor to fire coils. On 4-cylinder engines, power transistor "A" controls primary current of ignition coil "A" to fire spark plugs on cylinders No. 1 and 4 at same time. Power transistor "B" controls primary current of ignition coil "B" to fire spark plugs on cylinders No. 2 and No. 3 at same time. On V6 engines, companion cylinders No. 1 and 4, 2 and 5, and 3 and 6 are fired together.

ECM/PCM uses signals from CMP sensor to determine which coil to fire. ECM/PCM uses signals from CKP sensor to adjust timing. Additional inputs from VAF sensor, IAT sensor, BARO sensor, ECT sensor, closed throttle position sensor, ignition switch, PNP switch (automatic transmissions), knock sensor and VSS are used by ECM/PCM to optimize timing for operating conditions. When engine is cold or operated at high altitudes, ECM/PCM will advance timing.

Eclipse 2.4L, Galant 2.4L, Lancer 2.0L & Mirage 1.8L

Distributorless Ignition System (DIS) consists of 2 ignition coils with built-in ignition power transistors, ignition failure sensor, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor, and ECM/PCM. CMP sensor is located by camshaft. CKP sensor is located on front of engine near crankshaft.

Montero & Montero Sport

Distributorless Ignition System (DIS) consists of 3 ignition coils, ignition power transistor unit containing 3 transistors, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor and ECM/PCM. CMP sensor is located on front of engine by camshaft. CKP sensor is located on front of engine near crankshaft.

HALL EFFECT IGNITION SYSTEM

System is equipped with a Hall Effect distributor. Shutter(s) attached to distributor shaft rotate through distributor Hall Effect switch, also referred to as a Camshaft Position (CMP) sensor, which contains a distributor pick-up (a Hall Effect device and magnet). As shutter blade(s) pass through pick-up, magnetic field is interrupted and voltage is toggled between high and low. ECM/PCM uses this data along with Crankshaft Position (CKP) sensor data to control ignition timing and injector pulse width. Additional inputs from VAF sensor, IAT sensor, BARO sensor, ECT sensor, closed throttle position sensor, ignition switch, PNP switch (automatic transmission), and VSS are used by ECM/PCM to optimize timing for operating conditions.

Diamante, Eclipse 3.0L, Galant 3.0L & Mirage 1.5L

Ignition system consists of distributor assembly, Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor, ignition coil, ignition power transistor, knock sensor (if applicable) and ECM/PCM. The Hall effect type CMP sensor, coil and ignition power transistor are located in distributor assembly. When automatic transmission shifts gears, ignition timing is retarded. When engine is cold or operated at high altitude, ECM/PCM will slightly advance timing. If engine has knock sensor and engine is knocking, ECM/PCM will retard timing.

IGNITION TIMING CONTROL SYSTEM

Ignition timing is controlled by ECM/PCM. ECM/PCM adjusts timing based on various conditions such as engine temperature, altitude and detonation. Ignition timing is checked using a scan tool and is not adjustable.

EXHAUST GAS RECIRCULATION (EGR) CONTROL

System consists of EGR valve, EGR solenoid, vacuum control valve, hoses and ECM/PCM. EGR valve is opened by manifold vacuum passing through vacuum control valve. EGR solenoid works as a vacuum bleed between vacuum control valve and EGR valve. When EGR solenoid is off, vacuum is bled off so not enough vacuum exists at EGR valve to open EGR valve. When EGR solenoid is on, vacuum bleed is closed so that vacuum from vacuum control valve is applied to EGR valve.

When engine is cold, ECM/PCM signals EGR control solenoid valve to deactivate EGR system. When engine is warmed up, ECM/PCM will control EGR system operation according to engine operating conditions. OBD-II monitors EGR system via Manifold Differential Pressure (MDP) sensor.

EVAPORATIVE EMISSION CONTROL

Fuel Evaporation Emission Control (EVAP) system prevents fuel vapor from entering atmosphere. EVAP system consists of fuel tank, fuel overflow limiter valve (fuel vent valve), fuel cutoff valve, EVAP canister, purge solenoid valve, vent solenoid valve, Fuel Tank Differential Pressure (FTDP) sensor and connecting lines and hoses. EVAP system in some models may also include vent valve, leveling valve and/or liquid separator.

Fuel vapors from fuel tank are stored temporarily in EVAP canister until drawn into engine through intake manifold and burned. When ECM/PCM turns purge solenoid on, vapors are drawn from EVAP canister into intake manifold. When engine coolant temperature is low, or when intake air volume is low (idle), ECM/PCM turns solenoid off.

OBD-II system runs tests (monitors) on EVAP system to check for leaks. During EVAP system monitor, ECM/PCM seals EVAP system by closing purge solenoid valve and vent solenoid valve. Once EVAP system is closed, ECM/PCM uses input from FTDP sensor to monitor EVAP system pressure changes and calculates whether leak exists. If EVAP system leak is detected, MIL will illuminate and a DTC will set.

Purge solenoid valve is normally closed. When engine is off, fuel vapors are vented into EVAP canister. When engine is warmed to normal operating temperature and running at speeds greater than idle, ECM/PCM energizes purge solenoid valve, allowing vacuum to purge canister.

Canister vapors are then drawn through purge solenoid valve into intake manifold for burning. Purge solenoid valve remains closed during idle and engine warm-up to reduce HC (hydrocarbons) and CO (carbon monoxide) emissions. ECM/PCM also controls purge solenoid valve to test EVAP system for leaks.

Vent solenoid valve is located between canister and atmosphere. It is used by OBD-II to test EVAP system for leaks. Normally vent solenoid valve is off so that canister is vented to atmosphere. When monitoring for leaks, ECM/PCM commands vent solenoid valve on which closes EVAP canister atmospheric vent.

Fuel Overflow Limiter Valve

Fuel vent valve is located in fuel filler neck. It prevents overfilling of fuel tank.

Fuel Cutoff Valve

Fuel cutoff valve prevents fuel leaks if vehicle is rolled over in a accident.

POSITIVE CRANKCASE VENTILATION (PCV) VALVE

PCV valve operates in closed crankcase ventilation system. Closed crankcase ventilation system consists of PCV valve and ventilation hoses.

PCV valve is a one-way check valve located in valve cover. PCV valve plunger position is regulated by intake manifold vacuum which regulates flow of blow-by gasses. Blow-by gas flow is lessened when engine is under low load to maintain engine stability. Blow-by is increased when engine is under high load to improve crankcase ventilation. If engine backfires through intake manifold, PCV valve closes to prevent crankcase combustion.

MALFUNCTION INDICATOR LIGHT (MIL)

On OBD-II systems, MIL (CHECK ENGINE light) will illuminate only for emissions system related faults or deterioration. MIL comes on when ignition is turned on. MIL remains on for 5 seconds after engine has started, then will go out if no DTCs are stored in ECM/PCM memory. If an emission systems related fault occurs according to preset criteria, a DTC will set and MIL will illuminate. Any fault must be repaired and DTC cleared. If ECM/PCM determines that system has returned to normal, MIL will be turned off by ECM/PCM.