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 SYSTEMS
The intake system consists of an air intake duct, a resonator chamber, and an air cleaner element housed in its case. The resonator, located upstream of the air cleaner case, effectively reduces the intake noise level.
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TURBOCHARGER SYSTEM
The turbocharger system consists of a water-cooled turbocharger, air-cooled intercooler, wastegate control solenoid valve, etc. The outlet side turbine, rotated by exhaust gas pressure, rotates the inlet side turbine. As a result, the inlet side turbine compresses the intake air before it is delivered to the intake manifold. The intake air is heated when it passes through the turbocharger unit. The air is cooled as it passes through the intercooler. This turbocharger system controls the supercharging pressure according to changes in the atmospheric pressure. Even at a high altitude, therefore, the system offers stable performance without being affected by variations in atmospheric pressure.
Air Bypass Valve
When a throttle valve is suddenly closed, low air suction noise may occur due to a sudden rise of the air pressure in the passage between the turbocharger and throttle body. To prevent this, an air bypass valve and air passage are provided. The air bypass valve, actuated by the vacuum created by a sudden closure of the throttle valve, allows the suction air to bypass the turbocharger and flow directly upstream, thus lowering the pressure in the air passage.
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Intercooler
Since the intake air having passed through the turbocharger unit is heated to a very high temperature, the air itself is expanded, resulting in a lower supercharging charging efficiency. The intercooler is provided just before the throttle body to cool down the intake air and improve the supercharging efficiency. The intercooler is an air cooled type. The air delivered from the air duct provided at the engine hood flows through the core and cools the intake air passing through the intercooler.
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Turbocharger
The turbocharger is water-cooled. It utilizes a wastegate valve to adjust its supercharging pressure to an optimum level. The turbine is housed in a lightweight, thin-wall, heat-resistant casting. The compressor housing is made of thin-wall, aluminum alloy casting. The shaft for turbine and compressor is supported by a full-floating metal bearing system.
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Wastegate Control Solenoid Valve
The wastegate control solenoid valve switches the intake air pressure passages to the wastegate controller in response to signals from the ECM. When the solenoid valve is closed, the intake air pressure upstream of the turbocharger unit is applied to the wastegate controller. When the solenoid valve is opened, the intake air pressure downstream of the turbocharger unit (supercharged air pressure) is applied to the wastegate controller.
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INDUCTION CONTROL SYSTEM
There is a butterfly valve on the partition between the intake manifold's right bank and left bank chambers. This valve is operated by the induction valve actuator installed on the intake manifold. During operation of the engine, pressure waves are generated in the intake manifold. The pressure waves have an effect of improving air intake efficiency. To make the most of this effect, the direction of the pressure wave is changed by opening and closing the induction valve in accordance with the engine speed so that increased engine output torque is obtained in all speed ranges.
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COMPUTERIZED ENGINE CONTROLS
The ECM receives signals from various sensors and based on them, it determines the amount of fuel injected and the fuel injection timing. It performs the sequential fuel injection control over the entire engine operating range except during start-up of the engine. The amount of fuel injected depends upon the length of time the injector stays open. The fuel injection duration is determined according to varying operating condition of the engine. For the purpose of achieving highly responsive and accurate fuel injection duration control, the ECM performs a new feedback control that incorporates a learning feature. The sequential fuel injection control is performed such that fuel is injected accurately at the time when the maximum air intake efficiency can be achieved for each cylinder (i.e., fuel injection is completed just before the intake valve begins to open).
ENGINE CONTROL MODULE (ECM)
Note. Components are grouped into 2 categories. First category is INPUT DEVICES , which are components that control or produce signals monitored by ECM. Second category is OUTPUT SIGNALS , which are components controlled by ECM.
The on-board diagnostics (OBD-II) system detects and indicates a fault in various input and output components of the complex electronic control system. The Check Engine malfunction indicator lamp (MIL) in the combination meter indicates occurrence of a fault or trouble code. Further, against a sensor failure that may disable driveability, the fail-safe function is provided to ensure the minimal driveability. The OBD-II system incorporated with the vehicles within this engine family complies with Section 1968.1, California Code of Regulations (OBD-II regulation). When the system decides that a malfunction occurs, MIL illuminates. At the same time of the MIL illumination or blinking, a diagnostic trouble code (DTC) and freeze frame engine conditions are stored into the on-board computer. The OBD-II system stores freeze frame engine condition data (engine load, engine coolant temperature, fuel trim, engine speed and vehicle speed, etc.) into an on-board computer when it detects a malfunction. If the OBD-II system detects the various malfunctions including the fault of fuel trim or misfire, the OBD-II system first stores freeze frame engine conditions about the fuel trim or misfire. When the malfunction does not occur again for three consecutive driving cycles, MIL is turned "OFF", but DTC remains in the on-board computer. The OBD-II system is capable of communication with a general scan tool (OBD-II general scan tool) formed by ISO 9141 CARB. For further self-diagnostic system information, see appropriate SELF-DIAGNOSTICS article. ECM is located under right side of dash, behind glove box.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input usage on a specific model, see appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Available input signals include the following
A/C Switch
Detects "ON-OFF" operation of the A/C switch.
Atmospheric Pressure Sensor
The atmospheric pressure sensor converts pressure values into electric signals, and sends the signals to the ECM.
Scheme 9
Blower Fan Switch
Detects "ON-OFF" operation of the blower fan switch.
Camshaft Position (CMP) Sensor
- Baja, Forester, Impreza, Legacy, Outback 2.5L & Outback Sport - The camshaft position sensor is located on the left camshaft support. It detects the combustion cylinder at any given moment. The sensor generates a pulse when one of the bosses on the back of the left camshaft drive sprocket passes in front of the sensor. The ECM determines the camshaft angular position by counting the number of pulses. Internal construction and the basic operating principle of the camshaft position sensor are similar to those of the crankshaft position sensor. Two bosses are provided on the sprocket for Impreza WRX 2.0L and a total of seven bosses are arranged at four equally spaced locations (one each at two locations, two at one location, and three at one location) of the sprocket for Forester, Impreza, Legacy, Outback 2.5L and Outback Sport.
- Outback 3.0L - The camshaft position sensor is located on the right cylinder head. It detects the combustion cylinder at any given moment. The sensor generates a pulse when one of the slots on the back of the right camshaft plate passes in front of the sensor. The ECM detects the camshaft position by measuring the pulse. Three slots are provided on the plate.
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Crankshaft Position (CKP) Sensor
- Baja, Forester, Impreza, Legacy, Outback 2.5L & Outback Sport - The crankshaft position sensor is installed on the oil pump which is located in the front center portion of the cylinder block. The sensor generates a pulse when one of the teeth on the perimeter of the crankshaft sprocket (rotating together with the crankshaft) passes in front of it. The ECM determines the crankshaft angular position by counting the number of pulses. The crankshaft position sensor is a molded type which consists of a magnet, core, coil, terminals and other components. As the crankshaft rotates, each tooth aligns with the crankshaft position sensor. At that time, the magnetic flux in the sensor's coil changes since the air gap between the sensor pickup and the sprocket changes. This change in magnetic flux induces a voltage pulse in the sensor and the pulse is transmitted to the ECM.
- Outback 3.0L - The crankshaft position sensor is installed on the rear end of the cylinder block. The sensor generates a pulse when one of the teeth on the perimeter of the crankshaft plate (rotating together with the crankshaft) passes in front of it. The ECM determines the crankshaft angular position by counting the number of pulses. As the crankshaft rotates, each tooth of the crankshaft plate aligns with the crankshaft position sensor so that the magnetic flux in the sensor's coil changes since the air gap between the sensor pickup and the crankshaft plate changes. This change in magnetic flux induces a voltage pulse in the sensor and the pulse is transmitted to the ECM.
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Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature sensor is located on the engine coolant pipe. The sensor uses a thermistor whose resistance changes inversely with temperature. Resistance signals as engine coolant temperature information are transmitted to the ECM to make fuel injection, ignition timing, purge control solenoid valve and other control corrections.
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Exhaust Gas Temperature Sensor
The exhaust gas temperature sensor is located on the joint pipe and used to monitor the condition of the precatalytic converter.
Front Oxygen (A/F) Sensor
The front oxygen sensor uses zirconium oxide (ZrO2) which is a solid electrolyte, at portions exposed to exhaust gas. The zirconium oxide has the property of generating electromotive force when its sides are exposed to oxygen ions of different concentration and the magnitude of this electromotive force depends on how much the difference is. The front oxygen sensor detects the amount of oxygen in exhaust gases by making use of this property of the zirconium oxide material. The zirconium oxide material is formed into a closed end tube and its external surface is exposed to exhaust gases with smaller oxygen ion concentration, whereas its internal surface is exposed to atmospheric air. The external surface has a porous platinum coating. The sensor housing is grounded to the exhaust pipe and the inside is connected to the ECM through the harness to be able to use the current output from the sensor. The sensor incorporates a ceramic heater to improve its performance at low temperatures.
When rich air-fuel mixture is burnt in the cylinder, the oxygen in the exhaust gases is almost completely used in the catalytic reaction by the platinum coating on the external surface of the zirconia tube. This results in a very large difference in the oxygen ion concentration between the inside and outside of the tube, and the electromotive force generated is large.
When a lean air-fuel mixture is burnt in the cylinder, relatively large amount of oxygen remains in the exhaust gases even after the catalytic action, and this results in a small difference in the oxygen ion concentration between the tube's internal and external surfaces. The electromotive force in this case is very small.
The difference in oxygen concentration changes drastically in the vicinity of the stoichiometric air-fuel ratio, and hence the change in the electromotive force is also large. By using this information, the ECM can determine the air-fuel ratio of the supplied mixture easily. The front oxygen sensor does not generate much electromotive force when the temperature is low. The output characteristics of the sensor stabilize at a temperature of approximately 1,292°F (700°C)
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Front & Rear Oxygen (A/F) Sensor Heater Circuit
Detects abnormality in heater circuit of front and rear oxygen sensors.
Fuel Level Sensor
The fuel level sensor forms part of the fuel pump and is located in the fuel tank. The sensor outputs an electric resistance signal that varies with movement of its float to indicate the level of the fuel remaining in the tank.
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Fuel Tank Pressure Sensor
Detects the evaporation gas pressure in the fuel tank.
Fuel Temperature Sensor
Detects the temperature of the fuel in the fuel tank.
Ignition Switch
Detects operation of the ignition switch.
Intake Manifold Pressure & Air Temperature (IAT) Sensor
The intake manifold pressure sensor and the intake air temperature sensor are integrated into a single unit. The unit is mounted on the intake manifold and measures the absolute air pressure in the intake manifold as well as the temperature of the intake air. The measured pressure and temperature are converted into electrical signals and sent to the ECM. The ECM uses these signals to control injection and ignition timing as well as the fuel injection amount.
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Intake Air Temperature Sensor (IAT)
The intake air temperature sensor is located in the air cleaner case and detects the temperature of the intake air introduced through the air intake duct. The ECM uses the resistance signal from the sensor to correct the fuel injection amount.
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Intake Manifold Pressure Sensor
The intake manifold pressure sensor is attached to the top of the throttle body, and continuously sends to the engine control module (ECM) voltage signals that are proportional to intake manifold absolute pressures. The ECM controls the fuel injection and ignition timing based on the intake manifold absolute pressure signals in addition to other signals from many sensors and other control modules.
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Knock Sensor (KS)
The knock sensor is installed on the cylinder block, and senses knocking that occurs in the engine. The sensor is a piezo-electric type which converts vibration resulting from knocking into electric signals. In addition to a piezo-electric element, the sensor has a weight and case as its components. If knocking occurs in the engine, the weight in the case moves causing the piezo-electric element to generate a voltage. The knock sensor harness is connected to the bulkhead harness.
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Mass Air Flow & Intake Air Temperature Sensors
The mass air flow and the intake air temperature sensors are integrated into a single unit. The unit is mounted on the air cleaner case and measures the amount as well as the temperature of the intake air. The measured amount and temperature are converted into electrical signals and sent to the ECM. The ECM uses these signals to control injection and ignition timing as well as the fuel injection amount.
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Neutral Position Switch (M/T)
Detects if shift position is in neutral.
Oil Pressure Switch
The oil pressure switch is located in the front upper portion of the right cylinder block bank. The purpose of this switch is to monitor the operation of the oil pump as well as the lubricating oil pressure when the engine is running. When oil pressure does not build up (immediately after ignition switch is turned "ON" the diaphragm is pushed toward the cylinder block by the spring force (a force equivalent to the specified oil pressure). This closes the contact points, causing the oil pressure warning light in the combination meter to illuminate. When oil pressure reaches the specified value (after engine starts), after reaching the specified value of 2.1 psi (14.7 kPa ), the oil pressure pushes the diaphragm overcoming the spring force. This opens the contact points and the oil pressure warning light goes out.
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Park/Neutral Position (PNP) Switch
Detects shift positions.
Pressure Sensor
The pressure sensor is attached to the top of the throttle body, and continuously sends to the engine control module (ECM) voltage signals that are proportional to intake manifold absolute pressures. The ECM controls the fuel injection and ignition timing based on the intake manifold absolute pressure signals in addition to other signals from many sensors and other control modules.
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Rear Defogger Switch
Detects "ON-OFF" operation of the rear defogger.
Rear Oxygen (A/F) Sensor
The rear oxygen sensor is used to sense oxygen concentration in the exhaust gas. If the air-fuel ratio is leaner than the stoichiometric ratio in the mixture (i.e., excessive amount of air), the exhaust gas contains more oxygen. To the contrary, if the fuel ratio is richer than the stoichiometric ratio, the exhaust gas contains almost no oxygen. Detecting the oxygen concentration in exhaust gas using the oxygen sensor makes it possible to determine whether the air-fuel ratio is leaner or richer than the stoichiometric. The rear oxygen sensor has a zirconia tube (ceramic) which generates voltage if there is a difference in oxygen ion concentration between the inside and outside of the tube. Platinum is coated on the inside and outside of the zirconia tube as a catalysis and electrode material. The sensor housing is grounded to the exhaust pipe and the inside is connected to the ECM through the harness. A ceramic heater is employed to improve performance at low temperatures.
When rich air-fuel mixture is burnt in the cylinder, the oxygen in the exhaust gases is almost completely used in the catalytic reaction by the platinum coating on the external surface of the zirconia tube. This results in a very large difference in the oxygen ion concentration between the inside and outside of the tube, and the electromotive force generated is large.
When a lean air-fuel mixture is burnt in the cylinder, relatively large amount of oxygen remains in the exhaust gases even after the catalytic action, and this results in a small difference in the oxygen ion concentration between the tube's internal and external surfaces. The electromotive force in this case is very small.
The difference in oxygen concentration changes drastically in the vicinity of the stoichiometric air-fuel ratio, and hence the change in the electromotive force is also large. By using this information, the ECM can determine the air-fuel ratio of the supplied mixture easily. The rear oxygen sensor does not generate much electromotive force when the temperature is low. The output characteristics of the sensor stabilize at a temperature of approximately 572 to 752°F (300 to 400°C).
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Small Light Switch
Detects "ON-OFF" operation of the small light switch.
Starter Switch
Detects condition of engine cranking.
Sub-Compartment Fuel Level Sensor
This sensor detects the level of the fuel in the sub-compartment (the compartment in which the fuel pump is not located) and acts as part of the fuel transfer line when the jet pump is in operation to maintain the fuel in both compartments at the same level.
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Throttle Position (TP) Sensor
The throttle position sensor is mounted in the throttle body and linked to the throttle valve. The throttle position sensor sends the ECM voltage signal corresponding to the opening of the throttle valve. When the sensor's output voltage exceeds a predetermined level, the ECM interprets it as complete closure of the throttle valve. When the output voltage is at another predetermined level, the ECM recognizes that the throttle valve is at a wide open position. Since the output characteristics of the sensor change over years, the ECM is provided with a learning function to be able to interpret signals into throttle valve angles always correctly.
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Torque Control Signal (A/T)
Controls engine torque.
Vehicle Speed Sensor (VSS)
- A/T - The vehicle speed sensor is mounted on the transmission. The vehicle speed sensor generates a 16-pulse signal for every rotation of the front differential and sends it to the transmission control module (TCM). The signal sent to the TCM is converted there into a 4-pulse signal, and then sent to the ECM and the combination meter.
- M/T - The vehicle speed sensor is mounted on the transmission. The vehicle speed sensor generates a 4-pulse signal for every rotation of the front differential and sends it to the ECM and the combination meter.
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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 of each output component, refer to indicated system.
Canister Purge Control Valve (CPCV)
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Data Link Connector (DLC)
See SELF-DIAGNOSTIC SYSTEM .
Drain Valve
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Fuel Injector(s)
See FUEL CONTROL (MFI) under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Tank Pressure Control Solenoid Valve
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Idle Air Control (IAC) Solenoid Valve
- Baja, Forester, Impreza, Legacy, Outback 2.5L & Outback Sport - The idle air control solenoid valve is located in the throttle body and regulates the amount of intake air that flows bypassing the throttle valve into the intake manifold during engine idling. It is activated by a signal from the ECM in order to maintain the engine idling speed at a target speed. The idle air control solenoid valve is a stepping motor type solenoid-actuated valve which consists of coils, a shaft, a permanent magnet, a spring and a housing. The housing is an integral part of the throttle body. The stepping motor consists of two paired coils, the coils of each pair being arranged face to face with a shaft in between. The shaft has a screw at the end around which the permanent magnets are arranged. As current flows in the form of pulses through the paired coils sequentially while alternating the polarity, the "N" and "S" poles of the permanent magnets around the shaft are repelled by the same poles of the magnetism generated by the coils. This causes a nut externally fixed to the magnets and internally engaging with the screw of the shaft to turn. The shaft then goes upward or downward. This upward and downward motion of the shaft opens or closes the valve port, adjusting the amount of bypass air.
- Impreza WRX 2.0L & Outback 3.0L - The idle air control solenoid valve is located in the throttle body and regulates the amount of intake air that flows bypassing the throttle valve into the intake manifold during engine idling. It is activated by a signal from the ECM in order to maintain the engine idling speed at a target speed. The idle air control solenoid valve is a solenoid-actuated rotary valve consisting of a coil, rotary valve, spring and housing. The housing is an integral part of the throttle body and provided with a bypass air port whose opening area is changed by the rotary valve. for more information, see «IDLE SPEED»(/subaru/impreza-wrx/gdgg-2002-2005/remont/theory-operation/#engine-controls-theory-operation) under FUEL SYSTEM.
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Ignition Coil
See IGNITION SYSTEMS .
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
Purge Control Solenoid (PCS) Valve
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Self-Diagnostics
See SELF-DIAGNOSTIC SYSTEM .
Tachometer
See TACHOMETER under MISCELLANEOUS CONTROLS.
Tumble Generator Valves
A tumble generator valve is provided on each engine bank, between the intake manifold and intake air ports. The right bank tumble generator valve has butterfly valves for the No. 1 and No. 3 cylinders and the left bank tumble generator valve has those for the No. 2 and No. 4 cylinders. The two butterfly valves in each tumble generator valve are fitted on a single shaft that is driven by an actuator. The tumble generator valves are controlled by the ECM according to the coolant temperature and the time elapsed after start of the engine. When the engine is started, the butterfly valves are moved to the closing ends. In this state, the intake air flows at very high speeds passing through narrowed passages in the directions determined by the individual intake air ports in the cylinder head. This creates tumbling air motions in the cylinders, which enables lean mixtures to be ignited and thus harmful exhaust emissions to be reduced during engine start. The tumble generator valves are fully open when the engine is operating at an ordinary driving speed, allowing intake air to flow without being changed in direction and velocity.
Scheme 45
Vent Control Solenoid Valve (VCSV)
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Fuel Filter
The fuel filter located in the engine compartment, is a pressure-withstanding cartridge type. It has a filter element in a metal case. The fuel entering the filter flows from the perimeter of the element to the center of the filter and goes out from there.
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Fuel Pressure Regulator
The pressure regulator is installed at the injector end of the fuel supply line. It has a fuel chamber and spring chamber separated by a diaphragm. Fuel chamber is connected to the fuel supply line and the spring chamber is connected to the intake manifold. Fuel chamber also has a relief valve connected to the fuel return line through which fuel returns to the fuel tank. When the intake manifold vacuum increases, the diaphragm is pulled and the relief valve opens to decrease the fuel supply line pressure (or fuel injection pressure). When the intake manifold vacuum decreases, the diaphragm is pushed by the spring to increase the fuel supply line pressure. Thus, the difference between the fuel injection pressure and the intake manifold vacuum is kept at a constant level of 43.4 psi (299.1 kPa) for 2.5L and 3.0L engines and 43.0 psi (294 kPa) for 2.0L engines to precisely control the amount of injected fuel.
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Fuel Pump
The fuel pump consists of a motor, impeller, pump casing, pump cover, check valve and filter. It is located in the fuel tank and combined with the fuel level sensor into a single unit. The operation of this impeller type pump is very quiet. When the ignition switch is turned "ON", fuel pump relay is activated. Then the motor operates to rotate the impeller. As the impeller rotates, fuel in a vane groove of the impeller flows along the fuel passage into the next vane groove by centrifugal force. When fuel flows from one groove to the next, a pressure difference occurs due to friction. This creates a pumping effect. The fuel pushed up by rotation of the impeller then passes through the clearance between the armature and the magnet of the motor and is discharged through the check valve. When the fuel discharge pressure reaches the specified level, the relief valve opens and excess fuel is released into the fuel tank. In this manner, the relief valve prevents an abnormal increase in fuel pressure. When the engine and the fuel pump stop, spring force acts on the check valve to close the discharge port, so that the fuel pressure in the fuel delivery line is retained.
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ECM energizes fuel pump relay based on inputs from ignition switch and ignition coil. During cranking, cranking circuit supplies current to energize fuel pump relay. After engine starts and key is released to "RUN" position, ECM provides fuel pump relay ground. This activates fuel pump.
Jet Pump
The jet pump utilizes the velocity of fuel returning from the engine to produce negative pressure in it. Using the pumping effect produced by the negative pressure, the jet pump transfers fuel from the sub-compartment to the main compartment of the fuel tank. When the return line nozzle is clogged, the fuel sent back through the return line flows back into the fuel tank via the relief valve.
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Air Assist Injector Solenoid Valve
The air assist injector solenoid valve is located in the piping between the throttle body and the injector and secured to the intake manifold. This solenoid valve is opened or closed by the signals from the ECM, adjusting the flow rate of air supplied to the injector.
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Fuel Injectors
- Except Impreza WRX 2.0L - The MFI system employs top feed type fuel injectors with an air assist feature. Each injector is installed in the fuel pipe in such a way that the injector is cooled by fuel. The features of this type of fuel injector are as follows: High heat resistance. Low driving noise. Easy to service. Small size. The fuel injector injects fuel according to the valve open signal from the ECM. The needle valve is lifted by the solenoid which is energized on arrival of the valve open signal. Since the injector's nozzle hole area, the lift of valve and the fuel pressure are kept constant, the amount of fuel injected is controlled only by varying the duration of the valve open signal from the ECM. Fuel atomization is enhanced using assist air supplied from the idle air control solenoid valve passing through the passage formed in the intake manifold at the area in which each injector is installed. This contributes not only to higher combustion efficiency and higher output but also to cleaner exhaust emissions.
- Impreza WRX 2.0L - The MFI system employs top feed type fuel injectors. Each injector is installed in the fuel pipe in such a way that the injector is cooled by fuel. The features of this type of fuel injector are as follows: High heat resistance Low driving noise. Easy to service. Small size. The injector injects fuel according to the valve open signal from the ECM. The needle valve is lifted by the solenoid which is energized on arrival of the valve open signal. Since the injector's nozzle hole area, the lift of valve and the fuel pressure are kept constant, the amount of fuel injected is controlled only by varying the duration of the valve open signal from the ECM. The multi-hole nozzle makes it possible for the injector to produce fire fuel particles, which enhances the combustion efficiency and output performance of the engine.
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Idle Air Control (IAC)
The ECM activates the idle air control solenoid valve to control the bypass air flowing through the bypass passage in the throttle body depending on signals from the crankshaft position sensor, engine coolant temperature sensor, pressure sensor and A/C switch so that the proper idle speed for each engine load is achieved. The idle air control solenoid valve uses a duty-ratio-controlled solenoid which can continuously vary the opening area of the rotary valve. As the ECM increases the duty ratio, opening of the rotary valve increases so that the bypass air flow increases, and the engine idling speed becomes higher as a result. The bypass air control is necessary for
- Increasing idling speed when the air conditioning system and/or electrical loads are turned on.
- Increasing idling speed during early stage of warm up period.
- Obtaining dashpot function when the throttle valve is quickly closed.
- Prevention of engine speed variation during idling.
DISTRIBUTORLESS IGNITION
Note. Coil-on-plug technology is used on 2.0L and 3.0L. ECM directly controls power transistor to control ignition timing.
Distributorless ignition system (DIS) is controlled by ECM. ECM determines operating condition of the engine based on signals from the pressure sensor, engine coolant temperature sensor, intake air temperature sensor, crankshaft position sensor and other sources. It then selects the ignition timing most appropriate for the condition thus determined from those stored in its memory and outputs at that timing a primary current "OFF" signal to the ignitor to initiate ignition. This control uses a quick-to-response learning feature by which the data stored in the ECM memory is processed in comparison with information from various sensors and switches. Thus, the ECM can always perform optimum ignition timing taking into account the output, fuel consumption, exhaust gas, and other factors for every engine operating condition. Engine speed fluctuates during start of the engine, so the ECM cannot control the ignition timing. During that period, the ignition timing is fixed at 10° BTDC by using the 10° signal from the crank- shaft position sensor.
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- Baja, Forester, Impreza 2.5L, Legacy, Outback 2.5L & Outback Sport - Ignition coils are made integral with an ignitor. The ignition system is of a dual-ignition-coil design, each coil causing two plugs to generate sparks simultaneously. In response to the signal from the ECM, the ignitor supplies current to an ignition coil and the ignition coil supplies high-voltage current to a pair of spark plugs (No. 1 and No. 2 or No. 3 and No. 4) simultaneously.
- Impreza WRX 2.0L & Outback 3.0L - The engines use a direct ignition system with one ignition coil mounted for each cylinder (or spark plug). The secondary terminal of the ignition coil is in contact with the spark plug terminal nut. Since no spark plug cable is used, secondary voltage drop, leaks or other problems that are inherent in a system using spark plug cables do not occur. The result is high performance and high reliability.
Ignition Timing Advance Control
On all models, ignition timing advance is controlled by ECM. Based on sensor input signals, ECM adjusts ignition timing to preprogrammed advance and retard specifications.
When engine knock occurs, the KS generates a signal to ECM. ECM retards spark timing until engine knocking stops, then gradually advances spark timing.
EXHAUST GAS RECIRCULATION (EGR)
The EGR system aims at reduction of NOx by lowering the combustion temperature through recirculation of a part of exhaust gas into cylinders via the intake manifold. The EGR valve is controlled by the ECM according to the engine operating condition.
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Atmospheric Pressure Switching Solenoid
The atmospheric pressure switching solenoid closes the passage from the fuel tank to the air when the OBD-II system is activated to make a diagnosis.
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Canister
The canister is filled with charcoal that temporarily stores fuel vapors.
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Drain Filter
The drain filter is installed at the air inlet port of the vent control solenoid valve. It cleans the air taken in the canister through the vent control solenoid valve.
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The drain valve is located on the line connecting the drain filter and canister, just below the drain filter. The drain valve is forcibly closed by a signal from the ECM while the evaporation system diagnosis is being conducted.
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Fuel Cut Valve (FCV)
The fuel cut valve is built onto the evaporation pipe of the fuel tank cap. The rising level of the fuel in the fuel tank causes the float to move up and closes the cap hole so that no fuel can enter the evaporation line.
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Fuel Tank Cap
The fuel tank cap has a relief valve which prevents development of vacuum in the fuel tank in the event of a problem with the fuel vapor line. When there is no problem with the fuel vapor line, the filler pipe is sealed at portion (A) and by the seal pressed against the filler pipe end. If vacuum develops in the fuel tank, the atmospheric pressure forces the spring down to open the valve; consequently outside air flows into the fuel tank, thus controlling the inside pressure.
Scheme 68
Fuel Tank Pressure Control Solenoid Valve (FTPCSV)
The fuel tank pressure control solenoid valve is located in the evaporation line between the shut-off valve on fuel filler pipe and the fuel tank. It adjusts the fuel tank inside pressure under the control of the ECM. When the tank inside pressure becomes higher than the atmospheric pressure, the valve is opened allowing fuel vapors to be introduced into the canister. On the other hand, when the tank inside pressure becomes lower than the atmospheric pressure, external air is taken from the drain valve into the canister. The pressure control solenoid valve can also be electrically closed for the system diagnosis purposes.
Scheme 69
- Baja, Forester, Impreza, Legacy, Outback 2.5L & Outback Sport - The purge control solenoid valve is on the evaporation line between the canister and intake manifold. It is installed at the underside of intake manifold. When the purge control solenoid valve is opened by a signal from the ECM, the external fresh air entering the canister carries the fuel vapors into the collector chamber.
- Outback 3.0L - The purge control solenoid valve is on the evaporation line between the canister and throttle body. It is installed at the underside of intake manifold.
Scheme 70
Scheme 71
Scheme 72
Rollover Valve
The rollover valve prevents fuel from flowing out in the event the vehicle tips over.
Scheme 73
Shut-Off Valve
The shut-off valve is located at the top of the fuel filler pipe. When a filler nozzle is inserted into the filler pipe, the shut-off valve closes the evaporation line.
Scheme 74
Vent Valve
The vent valve is located on the fuel tank. During filling the fuel tank, fuel vapors are introduced into the canister through the vent valve. When the fuel vapor pressure becomes higher than the atmospheric pressure and overcomes the spring force which is applied to the back side of the diaphragm, the port toward the canister is opened. The vent valve also has a float which blocks the fuel vapor passage when the tank is filled up. Increasing fuel level raises the float to close the port toward the canister.
Scheme 75
POSITIVE CRANKCASE VENTILATION (PCV)
The positive crankcase ventilation (PCV) system prevents air pollution which will be caused by blow-by gas being emitted from the crankcase. The system consists of a sealed oil filler cap, rocker covers with fresh air inlet, connecting hoses, a PCV valve and an air intake duct.
In a part-throttle condition, the blow-by gas in the crankcase flows into the intake manifold through the connecting hose of crankcase and PCV valve by the strong vacuum created in the intake manifold. Under this condition, fresh air is introduced into the crankcase through the connecting hose of the rocker cover.
In a wide-open-throttle condition, a part of blow-by gas flows into the air intake duct through the connecting hose and is drawn into the throttle chamber, because under this condition, the intake manifold vacuum is not strong enough to introduce through the PCV valve all blow-by gases that increase in the amount with engine speed.
Self-diagnostic system monitors output signals through DLC. Diagnostic Trouble Codes (DTCs) can only be read using a scan tool connected to DLC. For additional information, see appropriate SELF-DIAGNOSTICS article.
DIAGNOSTICS OF AUTOMATIC TRANSMISSION
Detects the self diagnostics of the automatic transmission. See appropriate DIAGNOSTICS article in TRANSMISSIONS .
DIAGNOSTICS OF TCM (AUTOMATIC TRANSMISSION)
Detects the self diagnostics of the TCM. See appropriate DIAGNOSTICS article in TRANSMISSIONS.
All vehicles are equipped with MIL (CHECK ENGINE light) on instrument panel. Light comes on when ignition switch is turned on (bulb check), and when system malfunctions occur. For additional information, see appropriate SELF-DIAGNOSTICS article.
ECM provides signal to drive tachometer.
See also:
• INPUT DEVICES
• OUTPUT SIGNALS
• FUEL EVAPORATIVE SYSTEM