VARIABLE RESONANCE INDUCTION SYSTEM (VRIS - 2.5L)
2 shutter valves on 2.5L in the dynamic chamber changes intake runner effective length depending upon engine RPM. (Scheme 1) To improve torque output at low-to-medium engine RPM, intake runners are opened into a resonance chamber, providing improved cylinder filling. At high engine speed, shutter valve closes, shortening intake runner length and improving high RPM performance.
Scheme 1
COMPUTERIZED ENGINE CONTROLS
Computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions, while maintaining fuel economy and driveability.
CONTROL UNIT
Note. MX-6 and 626 use a Powertrain Control Module (Engine) (PCME). For the purpose of this article, PCM will be used to describe these control units.
Electronic Fuel Injection
The PCM, through various input sensors, monitors battery voltage, engine RPM, intake air volume, cranking signal, crankshaft angle, intake air temperature, radiator and engine coolant temperatures, exhaust oxygen content, throttle position, atmospheric pressure, gearshift lever position, clutch engagement, braking, power steering operation, and A/C compressor operation.
PCM uses this input information to control fuel injection and operation of other output devices. On MX-6 and 626, spark timing is controlled by PCM.
PCM has a built-in fail-safe mechanism. If a fault occurs while driving, PCM will substitute pre-programmed values. Driving performance will be affected, but vehicle may still be driven.
PCM has a self-diagnostic function, which allows unit to store a number of trouble codes in its memory. A Malfunction Indicator Light (MIL) informs the driver of system problems. MIL is in center of instrument cluster, under engine symbol marked CHECK.
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by PCM. The second category covers OUTPUT SIGNALS, which are components controlled by PCM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see appropriate wiring diagram at the end of this article. The available input signals include the following
Air Conditioning Switch
Switch closes when A/C or blower is on.
Airflow Meter Inlet Air Temperature Sensor
Sensor varies voltage signal to PCM in relation to inlet air temperature and is part of airflow meter.
Airflow Meter (Vc)
Corrected airflow meter voltage.
Airflow Meter (Vs)
Airflow meter flap or measuring cone position signal.
Airflow Sensor (2.0L)
Sensor uses an electrically heated hot wire to determine air mass entering engine.
Airflow Sensor (2.5L)
Sensor uses a measuring cone to determine air mass entering engine.
Atmospheric Pressure Sensor
Sensor varies voltage signal according to altitude.
Brakelight Switch
Switch signals PCM of vehicle braking condition.
Coolant Thermosensor
Thermosensor varies input voltage signal according to engine coolant temperature.
Coolant Temperature Switch
Switch opens and closes according to radiator temperature.
Crank Angle Sensor (2.0L)
Sensor signals No. 1 and 4 cylinder TDC for fuel injection and ignition timing. Sensor also detects crankshaft angle at 90-degree intervals to trigger ignition coils, providing PCM with data to control injection amount and injection timing.
Crank Angle Sensor (2.5L)
Sensor provides signals for fuel injection and ignition timing. Sensor also detects crankshaft angle at 60-degree intervals to trigger ignition coils, providing PCM with data to control injection amount and injection timing.
Distributor Signal(s)
Signals cylinder TDC (No. 1 on 4-cylinder engines, and No. 1 and 4 on V6 engines) for fuel injection timing. Some models use Light Emitting Diode (LED) sensors, while other models use magnetic pick-up coil(s) or Hall-Effect sensors to detect distributor shaft position.
EGR Position Sensor
Signals EGR control valve opening.
Electrical Load Control/CPU
Signals PCM of additional electrical load.
Hall-Effect Sensors
Hall-Effect sensors are used to detect position of a rotating shutter wheel. As each segment of the metal shutter wheel passes between the Hall-Effect sensor and a magnet, a change in current occurs. The Hall-Effect sensor responds to the change in magnetic field by switching a transistor on or off. This is used by PCM to detect the position of each cylinder or TDC of No. 1 cylinder.
Heated Oxygen Sensor
At operating temperature, Heated Oxygen Sensor (HO2S) monitors oxygen content of exhaust gases. A heating circuit is used to warm HO2S to operating temperature, enabling faster conversion of feedback system to closed loop operation.
HO2S produces low voltage (less than .4 volt) to indicate lean mixture (high amount of oxygen) and a high voltage (more than .6 volt) to indicate rich mixture (low amount of oxygen). This voltage signal is transmitted to PCM.
Idle Switch
Indicates throttle open or closed position.
Ignition Coil
Signals engine speed.
Ignition Switch
Supplies battery voltage to PCM during engine cranking.
Ignitor
Triggers coil and signals engine speed to tachometer.
Inhibitor Switch (A/T)
Signals PCM of gear selection.
Knock Sensor (2.5L)
Sends signal to knock control unit which retards ignition timing when knocking occurs.
Main Relay
Provides battery voltage to PCM and injectors.
Neutral/Clutch Switch (M/T)
Signals PCM of clutch operation and transaxle gear selection.
Oxygen (O2S) Sensor
Generates voltage signal depending on oxygen content of exhaust.
Throttle Position Sensor
Provides signal in response to throttle position.
Vehicle Speed Sensor (VSS)
Sends a pulsing signal to PCM when vehicle is moving.
OUTPUT SIGNALS
Note. Vehicles are equipped with various combinations of computer-controlled components. Not all components listed are used on every vehicle. For theory and operation of each output component, refer to system indicated after component.
The PCM processes information from input sensors and sends appropriate voltage control signals to the following engine controls
A/C Cut-Out System
See IDLE SPEED under FUEL SYSTEM.
BP/EGR-VRV
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
By-Pass Air Control (BAC) Valve
See IDLE SPEED under FUEL SYSTEM.
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
EGR-SOL
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
Fuel Pressure Regulator Control (FPRC) Solenoid
See FUEL DELIVERY under FUEL SYSTEM.
Heated Oxygen Sensor (HO2S) Element
See INPUT DEVICES - EFI.
Idle Speed Control (ISC) Valve
See IDLE SPEED under FUEL SYSTEM.
Ignition Timing Advance Control
See IGNITION TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Purge Solenoid
See FUEL EVAPORATION SYSTEM under EMISSION SYSTEMS.
Variable Inertia Charging System Solenoid
See AIR INDUCTION SYSTEM .
Variable Resonance Induction System Solenoid
See AIR INDUCTION SYSTEM .
Fuel Pump
Fuel, pressurized by electric fuel pump, flows through fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Pump is located in fuel tank. Electrical power for fuel pump operation during cranking mode is provided by starter relay, via fuel pump relay and PCM.
The PCM turns on fuel pump relay based on inputs from the ignition switch and the ignition coil. During cranking, ignition switch cranking circuit energizes fuel pump relay. After engine starts and key is released to RUN position (engine speed more than 50 RPM), PCM provides fuel pump relay ground.
Fuel Pressure Regulator
Pressure regulator is a sealed unit, divided into 2 chambers (fuel and spring chambers) by a diaphragm. The fuel chamber receives fuel through the inlet side of injector fuel rail. The spring chamber is connected to intake manifold vacuum.
At idle, intake manifold vacuum is high. The diaphragm is pulled back by intake manifold vacuum, and excess fuel is returned to fuel tank. As throttle opens, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.
FPRC system includes a solenoid connected to vacuum line of fuel pressure regulator. During hot engine restarts, PCM energizes FPRC. This prevents intake manifold vacuum from going to fuel pressure regulator and increases fuel pressure about 8 psi (.6 kg/cm 2 ).
High Pressure Fuel Pump
The high pressure fuel pump is positioned inside fuel tank (some models). A reservoir is built onto pump and sender assembly, instead of as part of tank. The high pressure fuel pump is capable of pumping over 16 gallons (60 liters) of fuel per hour at a working pressure of 39.2 psi (2.75 kg/cm 2 ). This pump also has internal pressure relief and discharge check valves.
Electronic Fuel Injection (EFI)
EFI system is an electronic-controlled system operated by incoming airflow. The EFI system also contains a feedback system, which measures oxygen content of exhaust gases and maintains air/fuel ratio near 14.7:1. The EFI system has 3 sub-systems: air intake system, fuel system and computerized engine control (PCM).
Each cylinder has a solenoid-operated injector, which sprays fuel toward back of each intake valve. Injector bodies consist of solenoid-actuated pintle and needle valve assembly. Injector flow orifice is fixed, and fuel pressure at injector tip is constant. Atomizing spray is obtained by shape of pintle.
PCM controls fuel injectors and meters pulse width or number of time each injector is energized. Each injector receives battery voltage through ignition switch circuit. PCM completes ground circuit to energize injector. PCM receives inputs from engine sensors to compute fuel flow necessary to maintain proper air/fuel mixture throughout entire engine operational range.
During acceleration (60 percent throttle or more with transmission in gear and clutch pedal released) and about 5 seconds after starting the engine, the ECA/PCM opens A/C relay, cutting off power to A/C compressor clutch. This improves idle after start-up and during heavy acceleration. A/C is cut off for about 10 seconds.
The BAC valve contains an air valve and Idle Speed Control (ISC) valve. Engine coolant is directed around the air valve, warming the thermowax element. (Scheme 2) When engine coolant temperature is less than 122°F (50°C), the wax is contracted and the engine idles fast. When coolant temperature is more than 122°F (50°C), the wax is fully expanded, closing valve.
The ISC valve, controlled by PCM, regulates air by-pass during cold and warm engine operation. During cold engine operation, the ISC valve opens, raising fast idle speed to a predetermined RPM. The ISC valve also compensates for all engine loads during warm engine operation to maintain a preset idle RPM.
Scheme 2
ISC valve, mounted on throttle body, controls idle smoothness by regulating throttle plate by-pass air. ISC valve consists of an air by-pass valve and idle speed control solenoid valve. Air by-pass valve functions during cold engine conditions, at temperatures less than 122°F (50°C). ISC solenoid valve works throughout entire temperature range. Air by-pass valve is affected by engine coolant temperature. ISC solenoid is controlled by PCM.
Idle is controlled by ISC air by-pass valve. Throttle air by-pass valve is a solenoid-operated valve controlled by PCM. Valve allows air to by-pass throttle plates to control cold engine fast idle, no-touch start, dashpot, over temperature idle boost and engine load idle correction.
Air by-pass channel carries idle airflow regulated by air by-pass valve. Air by-pass valve is controlled by PCM to adjust both cold and warm idle speeds. Air by-pass valve uses solenoid valve to vary idle airflow volume allowed to enter engine.
ELECTRONIC IGNITION SYSTEM
Hall-Effect sensors are used to detect position of a rotating shutter wheel. As each segment of the metal shutter wheel passes between the Hall-Effect sensor and a magnet, a change in current occurs. The Hall-Effect sensor responds to the change in magnetic field by switching a transistor on or off.
This signal is used by PCM to detect the position of each cylinder or TDC of cylinder No. 1. The PCM delivers ignition signals to the ignitor to control ignition. Ignitor triggers ignition coil.
All models use a PCM-controlled Electronic Spark Advance (ESA) system. The PCM determines ignition timing based on signals from input devices.
EMISSION SYSTEMS
Note. Not all listed components are used on every vehicle system. Component usage depends on calibration of vehicle. See VACUUM DIAGRAMS article in the ENGINE PERFORMANCE section.
DECELERATION CONTROL SYSTEM
Fuel injected engines include a system to reduce emission during deceleration during closed throttle and high RPM conditions. At speeds greater than 2000 RPM, PCM shuts off fuel injection whenever TP sensor detects closed throttle position.
EXHAUST GAS RECIRCULATION (EGR)
EGR system allows measured amounts of exhaust gas into intake manifold to reduce oxides of nitrogen (NOx).
The EGR system on MX-6 and 626 consists of EGR control valve, EGR solenoid valves (vacuum side and vent side), EGR position sensor (California), connecting hoses and pipes.
FUEL EVAPORATION SYSTEM
Fuel evaporation system prevents escape of raw fuel vapor to atmosphere. System components include fuel tank with integral vapor separator, check-and-cut valve, purge control solenoid valve, charcoal canister, fuel filler cap and connecting lines.
Additional components include a 2-way check valve and PCM.
Canister Purge Solenoid Valve
This normally closed solenoid valve controls fuel vapor flow from canister to intake manifold. Solenoid is opened or closed by a signal from PCM during various engine operating modes.
Vapor Vent System
All vapor valves are mounted on fuel tank and use a small orifice which allows vapor (but not liquid) fuel to pass into line running to canister. Fuel vapors in fuel tank are vented though vapor valve assembly on top of fuel tank. Vapors are routed through a vapor line to carbon canister in engine compartment.
POSITIVE CRANKCASE VENTILATION (PCV)
The PCV system uses intake manifold vacuum to eliminate crankcase pressure. Manifold vacuum draws gases from crankcase, through PCV hose, into combustion chamber. The PCV valve is positioned in hose through which crankcase gases flow on their way to combustion chamber.
By opening and closing in direct relation to engine vacuum, the PCV valve meters crankcase gas flow to combustion chamber. During periods of high manifold vacuum, such as at idle and deceleration, valve is almost completely closed, limiting flow of gases. During cruise speeds, valve permits greatest flow of gases.
Under conditions in which excessively high amounts of crankcase pressure is produced (such as heavy load), system allows excess gases to flow back through crankcase vent hose and into intake manifold.
Also called CHECK ENGINE light, MIL 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 the abnormal input signal returns to normal, PCM turns light off but code remains stored in memory until cleared. If ignition is turned on again, light will not come on until PCM detects another malfunction during system operation.
Note. PCM diagnostic memory is retained by direct power supply from battery. Memory is not erased by turning off ignition but is erased if battery or PCM is disconnected.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
FUEL PRESSURE REGULATOR CONTROL (FPRC)
During hot engine starts, intake manifold vacuum to the fuel pressure regulator is removed. This increases fuel pressure, which helps prevent vapor locking.
WIDE OPEN THROTTLE A/C (WAC) CUTOFF
During wide open throttle, WAC circuit interrupts power to A/C compressor clutch. The A/C remains off for about 3 seconds after returning from WOT.
