TRIPLE INDUCTION CONTROL SYSTEM (TICS)
All 3.0L engine cylinder heads have 3 valves per cylinder: 2 intake and one exhaust. To improve intake efficiency at idle and low RPM, the TICS closes a swirl control valve in the intake runners. (Scheme 1) This forces most of the intake air through a small passage called a swirl port, located below main intake runner. This causes a strong swirl in the combustion chamber, improving combustion and fuel economy.
VARIABLE INERTIA CHARGING SYSTEM (VICS)
Shutter valves in intake manifold control length of intake air path, depending upon engine RPM. At less than 5000 RPM, the shutter valves close, improving torque output. At more than 5000 RPM, the shutter valves open, increasing airflow while improving high RPM performance.
VARIABLE RESONANCE INDUCTION SYSTEM (VRIS) (3.0L ONLY)
A shutter valve in the dynamic chamber changes intake runner effective length depending upon engine RPM. (Scheme 2) 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.
TURBOCHARGER
MX-6 turbo and 626 turbo models use liquid-cooled (coolant) turbochargers, mounted directly to the exhaust manifold. Turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate.
The pressure-actuated wastegate is the system's safety valve, preventing excessive intake boost pressure. Wastegate operation is also controlled by the Electronic Control Unit (ECU). Engine knock control unit senses engine knock and sends this signal to ECU. The ECU opens a wastegate solenoid valve and lowers boost pressure up to 2.2 psi.
ELECTRONIC FUEL INJECTION
The Electronic Gas Injection (EGI) computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions, while maintaining fuel economy and driveability.
FEEDBACK CARBURETOR (B2200)
The Feedback Carburetor (FBC) computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions while maintaining fuel economy and driveability.
Scheme 1
Scheme 2
CONTROL UNIT
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the ECU. The second category covers OUTPUT SIGNALS, which are components controlled by the ECU.
The Electronic Control Unit (ECU), 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.
The ECU uses this input information in determining fuel injection and the actuation of other output devices. On Miata, MX-6 turbo, 626 turbo and all 929 models, spark timing is controlled by the ECU.
The ECU has a built-in, fail-safe mechanism. If a fault occurs while driving, the ECU will substitute pre-programmed values. Driving performance will be affected, but the vehicle may still be driven.
The ECU has a self-diagnostic function which allows the unit to store a number of trouble codes in its memory. A Malfunction Indicator Lamp (MIL) informs the driver of system problems. The MIL is in the center of the instrument cluster, under the engine symbol marked CHECK.
The Electronic Control Unit (ECU), through various input sensors, monitors battery voltage, engine RPM, amount of intake air, cranking signal, intake temperature, radiator and engine coolant temperatures, oxygen concentration in exhaust gases, EGR operation, throttle opening, atmospheric pressure, gearshift lever position, clutch engagement, and A/C compressor operation.
The ECU uses all input information to control air/fuel solenoid valve, idle-up solenoid valves, slow fuel-cut solenoid valve, coasting richer solenoid valve, vacuum solenoid valve, Air Control Valve (ACV) solenoid valve, purge solenoid valve, and duty solenoid valve. ECU has a built-in, fail-safe mechanism. If a fault occurs while driving, ECU will substitute pre-programmed values. Driving performance will be affected, but vehicle may still be driven.
INPUT DEVICES - ELECTRONIC FUEL INJECTION
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 in WIRING DIAGRAMS article. The available input signals include the following
AIR CONDITIONING SWITCH
Closes when A/C or blower is in the ON position.
AIRFLOW METER (INLET AIR TEMPERATURE)
Varies voltage signal to ECU in relation to inlet air temperature.
AIRFLOW METER (VC)
Corrected airflow meter voltage.
AIRFLOW METER (VS)
Airflow meter flap position signal.
AIRFLOW SENSOR (B2200, B2600I & MPV 2.6L)
The airflow sensor uses an electrically heated hot wire to determine the air mass entering the engine.
ATMOSPHERIC PRESSURE SENSOR
Varies voltage signal according to altitude.
BRAKE LIGHT SWITCH
Signals ECU of vehicle braking condition.
COOLANT TEMPERATURE SENSOR
Varies input voltage signal according to engine coolant temperature.
COOLANT TEMPERATURE SWITCH
Switch opens and closes according to radiator temperature.
CRANK ANGLE SENSOR (MIATA)
Signals No. 1 and 4 cylinder TDC for fuel injection and ignition timing. Detects crankshaft angle at 90 degree intervals to trigger ignition coils and provide ECU with data to control injection amount and injection timing.
DISTRIBUTOR SIGNAL
Signals cylinder TDC (No. 1 on 4-cylinder engines and No. 1 and 4 on V6 engines) for fuel injection timing. Detects crankshaft angle at 30 degree intervals.
EGR POSITION SENSOR (929 ONLY)
Signals EGR valve opening quantity.
ELECTRICAL LOAD CONTROL
Signals ECU of additional electrical load.
IDLE SWITCH
Indicates throttle open or closed position.
IGNITION COIL
Signals engine speed.
IGNITION SWITCH
Supplies battery voltage to ECU during engine cranking.
IGNITOR (3.0L ONLY)
Signals engine speed.
INHIBITOR SWITCH (A/T)
Signals ECU of gear selection.
INTAKE AIR TEMPERATURE SENSOR (DYNAMIC CHAMBER 2.6L & 3.0L)
Varies voltage signal to ECU in relation to engine air temperature. All 929 models except 929S use 2 intake air temperature sensors. One sensor is located inside the airflow meter, the other is located near the intake runner on cylinder head.
KNOCK SENSOR (929S & TURBO MODELS)
Sends signal to knock control unit which retards ignition timing when knocking occurs. On MX-6 turbo and 626 turbo, knock control unit reduces turbocharger boost pressure under knock condition.
MAIN RELAY
Provides battery voltage to ECU.
NEUTRAL/CLUTCH SWITCH (M/T)
Signals ECU of clutch operation and transaxle gear selection.
OXYGEN (O2) SENSOR
Generates voltage signal depending on oxygen content of exhaust.
THROTTLE SENSOR
Referred to as PSW switch. Provides signal in response to wide open throttle position.
Closes when A/C or blower switch is in the ON position.
Varies voltage signal according to altitude.
Varies input voltage signal according to engine coolant temperature.
Switch opens and closes according to radiator temperature.
CLUTCH SWITCH
Signals ECU of clutch engagement.
EGR POSITION SENSOR
Detects EGR operation, sends signal to ECU.
Indicates throttle closed position.
Signals engine speed.
Supplies battery voltage to ECU during engine cranking.
Signals ECU of gear selection.
INTAKE AIR TEMPERATURE SENSOR
Detects intake air temperature, sends signal to ECU.
Signals ECU of clutch operation and transaxle gear selection.
Generates voltage signal proportional to oxygen content of exhaust gases.
VACUUM SENSOR
Detects intake manifold vacuum, sends signal to ECU.
OUTPUT SIGNALS - ELECTRONIC FUEL INJECTION
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 of each output component, refer to the system indicated in brackets.
The ECU processes information from the input sensors and sends appropriate voltage control signals to the following engine controls
- A/C Cut-Out System (Idle Speed)
- By-Pass Air Control (BAC) Valve (Idle Speed)
- CHECK ENGINE Light (Self-Diagnostics)
- Ignition Timing Advance Control (Ignition System)
- Fuel Pump Relay (Fuel Delivery)
- Triple Induction Control System Solenoid (Air Induction)
- Variable Inertia Charging System Solenoid (Air Induction)
- Variable Resonance Induction System Solenoid (Air Induction)
OUTPUT SIGNALS - FEEDBACK CARBURETOR (B2200)
Note. For theory and operation on each output component, refer to system indicated in brackets.
The ECU processes information from input sensors and sends appropriate voltage control signals to the following engine controls
- CHECK ENGINE Light (Self-Diagnostics)
- Deceleration Control System (Emission Systems)
- Idle-Up Valve (Idle Speed)
During idle and light-to-medium engine load, the ECU actuates the TICS solenoid valve and vacuum is applied to the swirl control vacuum actuator within intake manifold. During heavy engine load and medium-to-high engine RPM, the ECU closes the TICS solenoid valve and vacuum is vented from swirl control actuator.
The ECU actuates the VICS solenoid depending upon engine RPM. At about 5000 RPM, the VICS solenoid actuates, allowing vacuum actuator to open shutter valve.
Variable Resonance Induction System (VRIS)
The ECU actuates the VRIS solenoid depending upon engine RPM. At 3700-5750 RPM, the VRIS solenoid activates, shutting off vacuum to shutter valve actuator, allowing actuator to vent vacuum. This closes shutter valve.
FUEL PUMP DELIVERY
Fuel under pressure from electric fuel pump flows through a fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Fuel pump is located in fuel tank. Electrical power for fuel pump operation during cranking mode is provided from starter relay, via fuel pump relay and ECU (fuel pump control unit on carbureted B2200 with A/T).
FUEL PUMP RELAY
The ECU turns on fuel pump relay, based on inputs from the ignition switch and the ignition coil. During cranking, the ignition switch cranking circuit energizes fuel pump relay. After engine starts and key is released to RUN position (engine speed more than 50 RPM), ECU provides fuel pump relay ground.
FUEL PRESSURE REGULATOR
The pressure regulator is a sealed unit, divided by a diaphragm into 2 chambers (fuel and spring chambers). 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. Excessive fuel is returned to the fuel tank. As the throttle is depressed, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.
The Electronic Gasoline Injection (EGI) system is an electronically controlled system operated by incoming airflow. The EGI system also contains a feedback system which measures oxygen content of exhaust gases and maintains the air/fuel ratio near 14.7:1. The EGI system consists of 3 sub-systems: air intake system, fuel system and computerized system (ECU).
The Mazda Feedback Carburetor (FBC) computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions, while maintaining fuel economy and driveability.
The Electronic Control Unit (ECU), through various input sensors, monitors battery voltage, engine RPM, amount of intake air, cranking signal, intake temperature, radiator and engine coolant temperatures, oxygen concentration in exhaust gases, EGR operation, throttle opening, atmospheric pressure, gearshift lever position, clutch engagement and A/C compressor operation.
The ECU uses input information to control output signals like air/fuel solenoid valve, idle-up solenoid valves, slow fuel-cut solenoid valve, coasting richer solenoid valve, vacuum solenoid valve, ACV solenoid valve, purge solenoid valve and duty solenoid valve.
ECU has a built-in fail-safe mechanism. If a fault occurs while driving, ECU substitutes pre-programmed values. Engine performance will be reduced, but vehicle can still be driven.
A/C CUT-OUT SYSTEM
During acceleration (60 percent throttle or more) and just after starting the engine, the ECU opens A/C relay, cutting off power to A/C compressor clutch. This improves idle after start-up and acceleration.
Under acceleration, the A/C will be cut off when the throttle valve is more than half open, transmission is in gear and clutch pedal is released (M/T only). A/C is cut off for about 10 seconds. A/C will also be cut off for about 5 seconds after the engine is started.
BY-PASS AIR CONTROL (BAC) VALVE
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. 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 Idle Speed Control (ISC) valve, controlled by ECU, 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 3
IDLE-UP SYSTEM (B2200 CARB)
The idle-up systems are used on those models with engine-powered accessories that decrease engine RPM. To maintain proper engine performance, the idle-up system increases idle RPM to required specifications.
The idle-up system consists of a idle-up solenoid valve, servo diaphragm, connecting hoses and electrical components. Models with A/C and A/T use a dual servo diaphragm.
DISTRIBUTORLESS IGNITION SYSTEM (MIATA)
The distributorless ignition system contains a crankshaft angle sensor to control ignition timing. Two individual ignition coils are used to send spark to cylinders No. 1 and No. 4, and No. 2 and No. 3. Paired cylinders will spark every complete crankshaft rotation (360 degrees).
The crank angle sensor, mounted on rear of intake camshaft, monitors No. 1 and No. 4 cylinder TDC, ignition and fuel injection reference points. Signals created by crank angle sensor are sent to the Electronic Control Unit (ECU).
The ECU delivers ignition signals to the ignitor to control ignition. Ignitor triggers appropriate ignition coil. Power for ignition coils is supplied from ignition switch.
ELECTRONIC IGNITION SYSTEM
Mitsubishi breakerless electronic ignition consists of an ignitor, ignition coil, pick-up coil and distributor. The control module is mounted inside the distributor with the pick-up coil assembly.
When ignition is on, ignition coil primary circuit is energized. As distributor shaft rotates, the reluctor rotates inside the stator assembly.
As armature teeth pass pegs of pick-up coil, a signal is sent to the ignitor. The ignitor then breaks the primary circuit in coil, causing high voltage surge in coil secondary circuit required to fire spark plugs.
IGNITION TIMING ADVANCE CONTROL
Miata, MX-6 turbo, 626 turbo and 929 use an ECU-controlled Electronic Spark Advance (ESA) system. The ECU determines ignition timing based on signals from input devices. All other models use centrifugal and vacuum advance units, located in distributor.
DECELERATION CONTROL SYSTEM (B2200 CARBURETED)
To reduce emissions and increase fuel economy during deceleration, a deceleration control system is used, consisting of a slow fuel-cut solenoid valve, a coasting richer solenoid valve, vacuum solenoid valve dash pot and mixture control valve.
Slow fuel-cut solenoid valve closes primary slow fuel passage on command from ECU. Coasting richer solenoid valve supplies extra air/fuel mixture to add to primary slow fuel on command from ECU. Vacuum solenoid valve supplies intake manifold vacuum to distributor vacuum advance on command from ECU. Dashpot closes throttle valve gradually. Mixture control valve release air into intake during first stage of deceleration.
EXHAUST GAS RECIRCULATION (EGR) CONTROL
The Exhaust Gas Recirculation (EGR) system allows measured amounts of exhaust gas into the intake manifold to reduce oxides of nitrogen (NOx).
The EGR system on B2200 models consists of EGR control valve, EGR valve position sensor, duty solenoid valve, connecting hoses and pipes.
The EGR system on MX-6 and 626 models consists of EGR control valve, EGR modulator valve (non-turbo), EGR solenoid valve (non-turbo), EGR position sensor (turbo), duty solenoid valve (turbo), vacuum check valve, connecting hoses and pipes.
The EGR system on 929 models consists of EGR control valve, EGR solenoid valves (vacuum side and vent side), EGR position sensor, 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 (3-way valve on MX-6 and 626), air vent solenoid valve (B2200 - carbureted), purge control solenoid valve (B2200 fuel injected and B2600i), 2 purge control valves (3 on 323, MX-6 and 626), charcoal canister, fuel filler cap, coolant thermovalve (except 323 and 929) and connecting lines.
Additional components include, a 3-way solenoid valve on MX-6 and 626 (2-way on 323 and 929) and Emission Control Unit (ECU).
HOT IDLE COMPENSATION SYSTEM (B2200 CARBURETED)
Hot idle compensation system supplies additional air to the intake manifold to maintain smooth idle and reduce emissions. When intake air temperature is more than 145°F (63°C), the idle compensator valve opens and allows air directly into the intake manifold.
REED VALVE AIR INJECTION (B2200 CARBURETED)
Air injection system draws atmospheric air into the exhaust system to reduce CO and HC emissions. Basic system components consist of a reed valve assembly, air control valve(s), catalytic converter(s) and connecting hoses and pipes.
THERMOSTATIC AIR CLEANER (B2200 CARBURETED)
The thermostatic air cleaner system controls temperature of air entering the carburetor depending on outside air temperature. Thermostatic air cleaner system consists of air cleaner housing, bimetallic control valve, flexible air hose and heat stove.
A control valve, controlled by air temperature, opens allowing warm air from heat stove to mix with fuel. This assists in engine warm up, better combustion and emission control.
CHECK ENGINE LIGHT
Check Engine light or Malfunction Indicator Light (MIL) illuminates during initial engine start and monitored component malfunction. MIL is also used to retrieve trouble codes.