Engine Controls - Theory & Operation: Other Mazda Tribute I

VARIABLE INERTIA CHARGING SYSTEM (PROTEGE & PROTEGE5 2.0L)

Shutter valves in the intake manifold control length of intake air path, depending upon engine RPM. With engine speed below 4750 RPM, the shutter valves close, improving torque output. At more than 4750 RPM, the shutter valves open, increasing airflow and improving high RPM performance.

VARIABLE RESONANCE INDUCTION SYSTEM (MILLENIA 2.5L & 626 2.5L)

The Variable Resonance Induction System (VRIS) uses 2 shutter valves in the dynamic chamber to change 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 airflow to the cylinder. At high engine speed, the shutter valves close, shortening intake runner length and improving high RPM performance. Millenia and 626 models are equipped with 2 VRIS shutter valve actuators and 2 VRIS solenoid valves.

Scheme 1

VARIABLE TUMBLE CONTROL SYSTEM (MIATA)

The shutter valve in the intake manifold lower runners closes at low RPM to improve emissions and fuel economy on California models. When the valve is closed, air follows through upper runner of intake and tumbles in the combustion chamber. The valve opens during high speed operation to allow full airflow through both runners and improves high RPM performance. The Variable Tumble Control System (VTCS) includes a shutter valve, shutter valve actuator, delay valve, solenoid, vacuum chamber and check valve.

INTAKE MANIFOLD COMMUNICATION CONTROL (MPV)

The Intake Manifold Communication Control (IMCC) actuator in the intake manifold controls the length of intake air path, depending upon engine RPM. With engine speed less than 3750 RPM, the IMCC actuator is energized, improving torque output. At more than 3750 RPM, the IMCC actuator is de-energized, increasing airflow while improving high RPM performance. The PCM monitors the IMCC actuator at all times.

COMPUTERIZED ENGINE CONTROLS

The Computerized engine control system monitors various engine/vehicle functions to control engine operation and lower emissions, while maintaining fuel economy and driveability.

POWERTRAIN CONTROL MODULE

The PCM, through various input sensors, monitors battery voltage, engine RPM, intake air volume, cranking signal, camshaft position, crankshaft position, intake air temperature, radiator and engine coolant temperatures, exhaust oxygen content, throttle position, EGR valve position, atmospheric pressure, gearshift lever position, clutch engagement, vehicle speed, braking, power steering operation, and A/C compressor operation.

The PCM utilizes this input information to control fuel injection system and operation of other output devices. Spark timing is also controlled by the PCM.

The PCM has a built-in fail-safe mechanism. If a fault occurs while driving, the PCM will substitute preprogrammed values. Driving performance will be affected, but vehicle may still be driven.

The PCM has a self-diagnostic function, which allows the module to store diagnostic trouble codes in its memory. A Malfunction Indicator Light (MIL), located on instrument cluster, informs driver of system problems.

ECM/PCM LOCATIONS

Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the PCM. The second category covers OUTPUT SIGNALS, which are components controlled by the 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 WIRING DIAGRAMS article. The available input signals include the following

A/C Amplifier

The A/C amplifier controls A/C operation according to vehicle conditions and sends A/C operating condition signal to the PCM.

A/C Pressure Switch

The A/C pressure switch detects A/C operation and sends signal to the PCM.

A/C Switch

The A/C switch indicates A/C request to the PCM.

Brake Switch

The brake switch signals the PCM of vehicle braking condition. May also be referred to as a Brake On/Off (BOO) switch.

Camshaft Position Sensor

The Camshaft Position (CMP) sensor detects camshaft angle at 180-degree intervals (4-cylinder) or 120-degree intervals (6-cylinder) and sends a signal to the PCM. The CMP sensor also detects cylinder No. 1 TDC (4-cylinder) or No. 1 and No. 4 TDC (6-cylinder) and sends a signal to the PCM. The CMP signal is used for fuel synchronization. For CMP sensor location, see CAMSHAFT POSITION SENSOR LOCATIONS table. On MPV, the CMP sensor pulses once per camshaft revolution.

CAMSHAFT POSITION SENSOR LOCATIONS

Closed Throttle Position Switch (Millenia 2.3L)

The Closed Throttle Position (CTP) switch, detects fully closed throttle plate position and sends a signal to the PCM. On Millenia 2.3L, the CTP switch is part of the TP sensor, which is adjusted automatically when the TP sensor is adjusted.

Clutch Pedal Position Switch (M/T)

The clutch pedal position switch signals the PCM of clutch operation.

Crankshaft Position Sensor

The Crankshaft Position (CKP) sensor detects crankshaft angle at 10-degree intervals on all models except Miata and Millenia. The Miata and Millenia are at 60-degree intervals. This provides the PCM with data to trigger the ignition coils.

Cylinder Head Temperature Sensor (B2300 & Tribute 2.0L)

All models except the B2300 pick-up and Tribute 2.0L, use an Engine Coolant Temperature (ECT) sensor. See ENGINE COOLANT TEMPERATURE SENSOR .

The Cylinder Head Temperature (CHT) sensor is a thermistor device which changes resistance proportionate to temperature changes. The CHT sensor inputs metal temperature of the cylinder head to the PCM. For CHT sensor location, see CHT & ECT SENSOR LOCATIONS table.

Differential Pressure Feedback EGR Sensor

See EXHAUST GAS RECIRCULATION SYSTEM under EMISSIONS SYSTEMS.

EGR Boost Sensor

The EGR boost sensor detects intake manifold pressure and sends a voltage signal to the PCM.

EGR Position Sensor

The EGR position sensor, detects the EGR control valve position and sends a signal to the PCM.

Engine Coolant Temperature Sensor

The B2300 pick-up & Tribute 2.0L use a Cylinder Head Temperature (CHT) sensor. See CYLINDER HEAD TEMPERATURE SENSOR .

The Engine Coolant Temperature (ECT) sensor is a thermistor device which changes resistance proportionate to temperature changes. The ECT sensor inputs engine coolant temperature to the PCM. For ECT sensor location, see CHT & ECT SENSOR LOCATIONS table.

CHT & ECT SENSOR LOCATIONS

Fuel Tank Pressure Sensor

The Fuel Tank Pressure (FTP) sensor inputs EVAP system pressure to the PCM.

Heated Oxygen Sensor

At normal operating temperature, the Heated Oxygen Sensor (HO2S) monitors oxygen content of exhaust gases. A heating element is used to warm the HO2S to operating temperature, enabling faster conversion of the feedback system to closed loop operation.

The HO2S produces low voltage (less than 0.4 volt) to indicate a lean mixture (high amount of oxygen) and a high voltage (more than 0.6 volt) to indicate a rich mixture (low amount of oxygen). This voltage signal is transmitted to the PCM. All models use more than one sensor.

Intake Air Temperature Sensor

The Intake Air Temperature (IAT) sensor inputs air temperature to the PCM. The IAT sensor changes resistance in response to air temperature. The IAT sensor resistance decreases as air temperature increases. For the IAT sensor location, see IAT SENSOR LOCATIONS table.

IAT SENSOR LOCATIONS

Knock Sensor

The Knock Sensor (KS) transmits a signal to the PCM which retards ignition timing when knocking occurs.

Main Relay

The main relay provides battery voltage to the PCM and injectors.

Mass Airflow Sensor

The Mass Airflow (MAF) sensor measures the flow of air entering the engine. This measurement of airflow is a reflection of engine load (throttle opening). Sensing element (hot wire) is a thin platinum wire wound on a ceramic bobbin and coated with glass.

Hot wire is maintained at 392°F (200°C) greater than cold wire (ambient) temperature. Cold wire is located downstream of hot wire. Air temperature is measured as intake air passes through the MAF sensor and over the cold wire sensor. PCM uses this information to control fuel delivery.

Manifold Absolute Pressure Sensor (B2300 & Millenia 2.3L)

Manifold Absolute Pressure (MAP) sensor varies voltage signal to PCM in relation to intake manifold pressure.

Neutral Switch

The neutral switch signals the PCM of transaxle gear selection.

Power Steering Pressure Switch

Power Steering Pressure (PSP) switch detects power steering operation and sends a signal to the PCM.

Throttle Position Sensor

The TP sensor provides a signal to the PCM in response to throttle plate position.

Transmission Range Sensor

Transmission range sensor signals the PCM of transaxle gear selection.

Vehicle Speed Sensor

The Vehicle Speed Sensor (VSS), located on the transmission, is a magnetic pickup type sensor that detects vehicle speed.

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 the 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.

A/C Relay

See IDLE SPEED under FUEL SYSTEM.

By-Pass Air Control Valve

See IDLE SPEED under FUEL SYSTEM.

Canister Purge Solenoid

See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.

EGR Valve

See EXHAUST GAS RECIRCULATION SYSTEM under EMISSION SYSTEMS.

Malfunction Indicator Light

See MALFUNCTION INDICATOR LIGHT under SELF-DIAGNOSTIC SYSTEM.

Fuel Injectors

See FUEL CONTROL under FUEL SYSTEM.

Fuel Pump

See FUEL DELIVERY under FUEL SYSTEM.

Fuel Pump Relay

See FUEL DELIVERY under FUEL SYSTEM.

Fuel Vapor Vent Valve

See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.

Idle Air Control Valve

See IDLE SPEED under FUEL SYSTEM.

Ignition Timing Advance Control

See IGNITION TIMING CONTROL SYSTEMS under IGNITION SYSTEMS.

Pressure Regulator Control Solenoid

See FUEL DELIVERY under FUEL SYSTEM.

Fuel, pressurized by the electric fuel pump, flows through the fuel filter, the fuel injector rail and the fuel pressure regulator. The pump is located in the fuel tank. The PCM controls the fuel pump relay ground circuit during run and start modes.

The PCM activates the fuel pump relay based on inputs from the ignition switch and the camshaft position (CMP) sensor. During cranking, the ignition switch cranking circuit energizes the fuel pump relay. After engine starts and key is released to RUN position (engine speed more than 50 RPM), the PCM provides the fuel pump relay ground.

Fuel Pressure Regulator

The fuel pressure regulator is a sealed unit, divided into 2 chambers (fuel and spring) by a diaphragm. The fuel chamber receives fuel through the inlet side of the fuel injector 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 the fuel tank. As throttle opens, intake manifold vacuum decreases. The regulator spring overcomes manifold vacuum, increasing fuel pressure.

The Pressure Regulator Control (PRC) system includes a solenoid connected with a vacuum line to the fuel pressure regulator. During hot engine restarts, the PCM energizes the PRC solenoid. This prevents intake manifold vacuum from going to the fuel pressure regulator and increases fuel pressure about 8 psi (0.6 kg/cm 2 ).

The PCM controls fuel injector "on" time (pulse width) to meter fuel quantity into the intake ports. The PCM receives inputs from several engine sensors to compute fuel flow necessary to maintain correct air/fuel operation throughout engine operating range.

Each cylinder has a solenoid-operated injector that sprays fuel toward each intake valve. Each injector receives battery voltage from the main relay. A PCM-controlled ground circuit is used to complete the circuit and energize the injector. Fuel injectors "fire" sequentially (in engine firing order) once per complete cycle.

Injectors consist of solenoid-actuated pintle and needle valve assembly. The amount of fuel delivered to the engine is regulated by length of time the solenoid is energized (pulse width). The atomized spray pattern is obtained by the shape of the injector pintle.

During acceleration (60 percent throttle or more with transmission in gear and clutch pedal released) and about 2-5 seconds after starting the engine and during heavy acceleration, the PCM opens the A/C relay, cutting off power to the A/C compressor clutch. This improves idle after start-up and performance during heavy acceleration.

The By-Pass Air Control (BAC) valve contains an air valve and Idle Air Control (IAC) 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, opening the air valve, enabling fast idle speed. When coolant temperature is more than 122°F (50°C), the wax is fully expanded, closing the valve.

Idle Air Control (IAC) valve is an electromechanical device controlled by the PCM. The IAC valve is mounted on the throttle body and allows air to by-pass the throttle plate. The amount of air allowed to by-pass the throttle plate is determined by the PCM and is controlled by a duty signal.

During cold engine operation, the IAC valve opens, raising idle speed to a predetermined RPM. The IAC valve also compensates for all engine loads during warm engine operation to maintain a preset idle RPM.

Except Millenia 2.3L & Tribute 3.0L

The ignition system consists of a Camshaft Position (CMP) sensor, Crankshaft Position (CKP) sensor and PCM. On B2300 pick-up and Tribute 2.0L, one 4-tower coil pack containing two coils is used. On B3000, B4000 pick-ups and MPV, one 6-tower coil pack is used. On Miata, Protege and Protege5, ignition coils are mounted on spark plugs No. 2 and 4, and have high tension leads connected to spark plugs No. 1 and 3.

During system operation, the PCM receives information from the CKP and CMP sensors. The PCM responds with a signal containing advance or retard timing information, which is sent to fire the ignition coils.

The CKP sensor is an electromagnetic device that senses movement of a 35 tooth wheel, located behind the crankshaft pulley. Each tooth is positioned in 10 degree increments with an empty slot (missing tooth) located BTDC. Detection of the missing tooth is what enables the PCM to identify crankshaft position and initiate correct firing order.

The PCM controls spark timing and coil firing, based on information from the CKP sensor. The ignition coils , are triggered by the PCM in pairs (On 4-cylinder models, cylinders No. 1 and 4 and No. 2 and 3. On 6-cylinder models, cylinders No. 1 and 4, No. 2 and 5 and No. 3 and 6.). One plug is fired on the compression stroke; the other plug fires on the exhaust stroke. On the next cycle, firing strategy is reversed.

Millenia 2.3L & Tribute 3.0L

The distributorless ignition system uses the Camshaft Position (CMP) sensor to control ignition timing. On Millenia and Tribute, six individual ignition coils are used, one located on each spark plug.

The CMP sensor, located at front of engine, monitors TDC of cylinder No. 1 and crankshaft angle at 180-degree intervals. Signals created by the CMP sensor are sent to the PCM.

The PCM delivers ignition signals to trigger the appropriate ignition coil. The PCM controls spark timing and coil firing, based on information from the CKP sensor. Power for the ignition coils are supplied from the ignition switch.

ELECTRONIC IGNITION SYSTEM (MILLENIA 2.5L)

Distributor consists of a CMP sensor, an ignition control module and ignition coil. The ignition coil is integrated into the ignition control module. When the ignition switch is on, ignition coil primary circuit is energized. As the distributor shaft rotates, the reluctor rotates inside the stator assembly.

When the armature teeth pass the CMP sensor, a signal is sent to the PCM. The PCM sends a signal to the ignition control module triggering coil, causing high voltage required to fire the spark plugs. The PCM controls spark timing and coil firing, based on information from CKP sensor.

All models use a PCM-controlled Electronic Spark Advance (ESA) system. The PCM determines ignition timing based on signals from several 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.

DECELERATION CONTROL SYSTEM

Fuel injected engines include a system to reduce emissions and prevent overheating of the Three Way Catalytic (TWC) converter during deceleration, closed throttle and high RPM conditions. At speeds greater than 2400 RPM, the PCM shuts off fuel injection whenever the TP sensor detects closed throttle position.

EXHAUST GAS RECIRCULATION SYSTEM

The EGR system allows controlled amounts of exhaust gas into the intake manifold to reduce oxides of nitrogen (NOx) and improve fuel economy.

The EGR system on the B2300, B3000, B4000 pick-ups and Tribute consists of a control valve, Differential Pressure Feedback EGR (DPFE) sensor, EGR Vacuum Regulator Solenoid (EGR-VRS), connecting hoses and pipes.

The EGR system on the Miata consists of an electronically operated EGR valve, boost sensor and boost sensor solenoid valve. The EGR valve has 4 coils that may be operated individually by the PCM as needed.

The EGR system on the Millenia consists of a control valve, boost solenoid valve/MAP sensor, solenoid valves (vacuum side and vent side), position sensor, connecting hoses and pipes.

The EGR system on the MPV consists of a control valve, boost sensor, boost sensor solenoid valve, connecting hoses and pipes.

The EGR system on the Protege and Protege5 consists of a control valve, boost sensor, boost sensor solenoid valve, position sensor and connecting hoses and pipes.

The EGR system on 626 consists of an EGR control valve, boost sensor, boost sensor solenoid valve, solenoid valves (vacuum side and vent side), position sensor, connecting hoses and pipes.

FUEL EVAPORATIVE SYSTEM

Fuel Evaporative (EVAP) system prevents escape of raw fuel vapor to atmosphere. System components may include the fuel tank with integral vapor separator, vent cut valve or check-and-cut valve, purge solenoid valve, charcoal canister, rollover valve(s), Fuel Tank Pressure (FTP) sensor, catch tank, 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 the charcoal canister to the intake manifold. The solenoid is opened or closed by a signal from the PCM during various engine operating modes.

Fuel Vapor Vent Valve System

The Fuel Vapor Vent (FVV) valve assembly is mounted on fuel tank and use a small orifice which allows fuel vapor (not liquid) to pass into the line running to the charcoal canister. Fuel vapors in the fuel tank are vented though the FVV valve assembly. Fuel vapors are routed through a vapor line to the charcoal canister in the engine compartment.

POSITIVE CRANKCASE VENTILATION

The PCV system uses intake manifold vacuum to eliminate crankcase pressure. Manifold vacuum draws gases from the crankcase, through the PCV hose and valve, into combustion chamber.

By opening and closing in direct relation to engine vacuum, the PCV valve meters crankcase gas flow to the combustion chamber. During periods of high manifold vacuum, such as at idle and deceleration, the PCV valve is almost completely closed, limiting the flow of gases. During cruise speeds, the PCV valve permits the greatest flow of gases.

Under conditions in which excessively high amounts of crankcase pressure are produced (such as heavy load), the PCV system allows excess gases to flow back through the crankcase vent hose and into the intake manifold.

Also called CHECK ENGINE light, the Malfunction Indicator Light (MIL) illuminates when the ignition switch is turned on. The light remains on for several seconds after the engine has started. If an abnormal input signal occurs, the MIL stays illuminated and Diagnostic Trouble Code (DTC) is stored in memory. If the abnormal input signal returns to normal, PCM turns light off but DTC remains stored in memory until cleared. If the ignition switch is turned on again, the MIL will not stay illuminated, until the PCM detects another malfunction during system operation.

Note. The PCM diagnostic memory is retained by a direct power supply from the battery. Memory is not erased by turning off the ignition switch, but is erased if the battery or PCM are disconnected.

MISCELLANEOUS CONTROLS

Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.

A/C CLUTCH CYCLING PRESSURE SWITCH

On models with a manual A/C system, the A/C Clutch Cycling Pressure Switch (CCPS) is mounted on top of the receiver-drier. Based on refrigerant system pressure, a signal is sent to the PCM. The PCM uses this signal to maintain system pressure within the programmed range.

VARIABLE VALVE TIMING (MIATA)

The Variable Valve Timing (VVT) system continuously varies the open/close timing of the intake valves under all driving conditions, city or highway, low or high speed. System consists of variable valve timing actuator and an Oil Control Valve (OCV). (Scheme 2) The OCV operates in conjunction with the PCM that monitors engine RPM, the Mass Air Flow (MAF) sensor and the Engine Coolant Temperature (ECT) sensor.

Scheme 2

WIDE OPEN THROTTLE A/C CUT-OFF

During wide open throttle, Wide Open Throttle A/C Cut-Off (WAC) circuit, interrupts power to the A/C compressor clutch. The A/C clutch remains off for about 3 seconds after returning from Wide Open Throttle (WOT).