INTRODUCTION
This article covers basic description and operation of EEC engine performance-related systems and components. Before diagnosing vehicles or systems with which you are not completely familiar, read this article. EEC systems are also referred to as Non-North American Operation (Non-NAO) systems.
TURBOCHARGERS
Turbocharger is an option on the Probe 2.2L. On acceleration, turbocharger boost pressure is controlled by a wastegate/actuator assembly. Operation of the wastegate is controlled by a solenoid valve. If a fault develops in the system, boost pressure will not be controlled and overboost will occur. If overboost occurs, the knock control system will retard spark advance and ECA will activate overboost warning chime.
The turbocharger assembly includes the following: turbine, compressor, wastegate, actuator and intercooler. The turbocharger system includes the following: boost control solenoid, intercooler, knock sensor, knock control unit, overboost warning device and vane air temperature sensor.
Boost Control Solenoid (BOOST)
The boost control solenoid determines turbocharger effect by regulating vacuum signal to wastegate actuator. When boost solenoid is de-energized, vacuum signal is applied to wastegate actuator, and boost pressure is reduced.
When boost solenoid is energized, vacuum signal is vented to atmosphere. The reduced vacuum signal is not enough to pull actuator linkage, and boost pressure is allowed to increase.
Exhaust Turbine & Compressor Assembly
Turbocharger uses exhaust gas to power the turbine assembly. Exhaust gas moving across the turbine blades causes blades to spin. The compressor, rotating on the same shaft as the turbine, draws air from the air cleaner and pumps it through the intercooler, into the intake plenum. An increase in exhaust gas volume will increase turbine and compressor speed. Faster rotation of the turbine increases compressor output. This process increases horsepower by pressurizing the air/fuel charge before entering combustion chamber.
The turbine and compressor wheels can reach speeds of up to 180,000 RPM. A sufficient supply of clean engine oil is necessary for continued operation. Engine oil is fed directly to center housing rotating assembly. Any contamination or interruption of oil flow will result in severe turbocharger damage.
Intercooler
An intercooler is used on turbocharged engines to lower inlet air temperature and increase inlet air density, allowing a denser air/fuel charge to enter the combustion chamber.
Wastegate & Actuator
When intake manifold pressure reaches a specified level, the wastegate opens, allowing a portion of the exhaust gas to by-pass the turbine blades to limit turbine speed and output.
The actuator responds to boost pressure, and is controlled by the ECA. When the pressure differential across the compressor reaches a specified level, the diaphragm will partially open the wastegate.
High Speed Inlet Air (HSIA) System (1.8L)
The HSIA system controls the length of intake air path to the intake manifold. The intake track is varied by opening and closing a shutter valve located inside the intake plenum. (Scheme 1) The HSIA solenoid directs vacuum to shutter valve, when RPM is less than 5000, to hold the shutter valve closed. This shortens the intake air path.
When engine RPM exceeds 5000 RPM, the HSIA solenoid vents vacuum to atmosphere, allowing shutter valve to open. This lengthens the intake air path. The vacuum reservoir ensures constant vacuum supply when manifold vacuum is low. The result is more engine torque in a wider range, at less than 5000 RPM.
Scheme 1
CONTROL UNIT
The ECA is a computer which receives data from numerous sensors, switches and relays. The ECA calibrates information received, and generates output signals to control various relays, solenoids and actuators. The ECA has failure detection and self-diagnosis capability.
On 2.2L non-turbo engines with A/T, the ECA also controls the 4-speed Electronic Automatic Transaxle (4EAT) microprocessor. On all models, the ECA is located on the center console behind the kick panel.
Note. Components are grouped into 2 categories. The first category covers INPUT DEVICES, which control or produce voltage signals monitored by the control unit. The second category covers OUTPUT SIGNALS, which are components controlled by the control unit.
Barometric Pressure (BP) Switch
Measures barometric pressure of atmosphere. The BP sensor affects air/fuel ratio and idle speed. The sensor is located inside the ECA and cannot be serviced separately.
Brake On-Off (BOO) Switch
The BOO switch is mounted on the brake pedal. It signals deceleration to the ECA for air/fuel ratio adjustment.
Clutch-Engage Switch
This switch is mounted at the clutch pedal. It tells the ECA when transmission is in gear. Signal of the clutch-engage switch to ECA affects air/fuel ratio, idle speed, and ignition timing (2.2L turbo).
Coolant Temperature Sensor
See ENGINE COOLANT TEMPERATURE (ECT) SENSOR.
Crankshaft Position Sensor (CPS)
The ECA uses CPS input to determine engine speed. On 1.8L engines, the CPS is incorporated with the Cylinder Identification (CID) photo sensor mounted inside the distributor. A slotted (5) disc rotates with the distributor shaft, passing through the photo sensor. As the slots pass through the sensor, the ECA calculates crankshaft position and engine speed. This signal affects air/fuel ratio, ignition timing, injector timing, idle speed, canister purge flow and A/C cutoff.
On 2.2L turbo engines, CPS sensor is located in the distributor base. It uses the rotation of a 24-tooth rotor mounted on the distributor shaft to detect crankshaft position. The signal generated is sent to ECA, which uses the signal to determine engine RPM. This signal affects air/fuel ratio, injector timing, idle speed, EGR flow, canister purge flow, fuel pressure, turbo boost pressure and ignition timing.
Cylinder Identification (CID) Sensor
On 2.2L non-turbo engines, CID sensor is not used. On all other models, CID sensor is located inside the distributor. On 1.8L models, a fixed-position, photo-sensor-type CID unit and CID disc are used. On 2.2L turbo models, 2 fixed-position, magnetic pick-up CID units and CID rotor are used.
On 1.8L engines, a slotted disc rotates with the distributor shaft and passes through the CID photo sensor. As the slot passes through the sensor, TDC compression stroke of cylinder No. 1 is indicated to the ECA. This signal affects injector timing.
On 2.2L turbo engines, a rotor is mounted on the distributor shaft and rotates past 2 fixed magnets. As the rotor passes the magnets, TDC of cylinder No. 1 and No. 4 are identified. This signal affects injector timing and ignition timing.
Idle Switch
The idle switch detects when throttle is closed and sends signal to ECA, indicating idle conditions are present. On 1.8L engines, idle switch is incorporated with throttle position sensor. On 2.2L models, idle switch is mounted separately near throttle shaft.
On 1.8L engines, this signal affects air/fuel ratio, idle speed, injector timing, fuel pressure and purge flow. On 2.2L models, this signal affects air/fuel ratio, injector timing (turbo) and EGR flow (turbo).
Exhaust Gas Oxygen (EGO) Sensor
The voltage signal produced by EGO sensor indicates oxygen content of engine exhaust gases. EGO sensor is threaded into exhaust manifold.
EGR Valve Position (EVP) Sensor
EVP sensor detects EGR valve position, and transmits information to the microprocessor. Sensor is mounted on EGR valve. The EVP signal affects EGR flow and ignition timing.
Engine Coolant Temperature (ECT) Sensor
Sensor inputs coolant temperature to ECA. Sensor is threaded into an engine coolant passage near thermostat housing. Signal from ECT sensor affects the following
- Air/Fuel Ratio
- Boost Pressure (2.2L Turbo)
- EGR Flow
- Fuel Pressure
- Idle Speed
- Ignition Timing (1.8L & 2.2L Turbo)
- Injector Timing (2.2L Turbo)
- Purge Flow
Knock Control Unit (2.2L Turbo)
This control unit is used on Probe with turbo engines. It monitors signal sent to ECA to determine whether knock sensor signal is due to pre-ignition or vibration. The ECA uses signal to retard ignition timing. Knock control unit is mounted on the firewall.
Knock Sensor (2.2L Turbo)
The knock sensor measures vibrations and converts them into an electrical signal. The signal is sent to the knock control unit, where it is filtered and sent to ECA. The knock sensor is threaded into the engine block, near the oil pressure switch.
Manual Lever Position (MLP) Switch
On vehicles with A/T, the MLP monitors shift lever positions and signals the ECA and transaxle control module. On 1.8L engines, this signal affects starter engagement, air/fuel ratio, idle speed, ignition timing, fuel pressure, canister purge flow and A/C cutoff. On 2.2L models, this signal affects starter engagement, air/fuel ratio, idle speed, and ignition timing (2.2L turbo).
Neutral Gear Switch (NGS)
On vehicles with M/T, the NGS monitors in-gear conditions and signals the ECA. On 2.2L engines, this signal affects air/fuel ratio, idle speed, and ignition timing (turbo). On 1.8L models, this signal affects air/fuel ratio, idle speed, ignition timing, fuel pressure, canister purge flow and A/C cutoff.
Power Steering Pressure Switch (PSPS)
The PSPS switch monitors power steering pressure. When power steering is in operation, the switch signals the ECA. The switch is located in the high-pressure line, from P/S pump to steering rack assembly. The PSPS signal affects idle speed and A/C cutoff (1.8L).
Self-Test Output/Self-Test Input (STO/STI) Connectors
The STO terminal is used to perform self-test diagnostic procedure. The STI is located next to the STO. When STI is grounded, it activates fault code output function. Codes are retrieved through STO terminal.
Throttle Position Sensor (TPS)
TPS monitors throttle plate opening. Its signal to ECA is proportional to opening angle. It is mounted on throttle body, at throttle plate rod. Signal of TPS affects A/C cutoff, air/fuel ratio, injector timing, idle speed, ignition timing (except turbo), EGR flow, fuel pressure, and purge flow (1.8L). If a malfunction is detected in TPS system, a code will be set in ECA memory.
Vane Airflow Meter (VAF)
The VAF is mounted in the air inlet, between air cleaner and throttle body. It measures the volume of air entering into the engine by monitoring the position of a movable door. A potentiometer, attached to VAF door, signals door position to the ECA. The ECA translates door position to volume of air entering the engine.
The VAF also contains a temperature sensor. The temperature of air entering the engine is monitored and transmitted to the ECA. The ECA is programmed to compute airflow and air temperature, so fuel flow can be adjusted to obtain optimum air/fuel mixture. The VAF also contains a fuel pump switching circuit to cut fuel pump operation when the engine is off.
On 1.8L models, this signal affects air/fuel ratio, injector timing, ignition timing and canister purge flow. On 2.2L models, this signal affects air/fuel ratio ignition timing (turbo) and canister purge flow.
Vane Air Temperature (VAT) Sensor
The Vane Air Temperature (VAT) sensor is mounted in the VAF. It monitors temperature of incoming air and inputs signal to the ECA. This signal affects air/fuel ratio, idle speed, fuel pressure, and turbo boost pressure on turbo engine.
On 1.8L models, this signal affects air/fuel ratio, idle speed, canister purge flow and fuel pressure. On 2.2L models, this signal affects air/fuel ratio, idle speed and fuel pressure.
Vehicle Speed Sensor (VSS)
Sensor is transmission mounted, and sends a constant pulse signal to ECA when vehicle is in motion.
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 on each output component, refer to the system indicated after component. The information referenced is contained in this article. To get to the information quickly, press the "F10" key in the lower right corner of the screen to exit to the subject menu and select the appropriate title.
- Canister Purge Solenoid - See EMISSION SYSTEMS.
- CHECK ENGINE Light - See SELF-DIAGNOSTIC SYSTEMS.
- Cooling Fan - See MISCELLANEOUS CONTROLS.
- EGR System - See EMISSION SYSTEMS.
- Fuel Injectors - See FUEL CONTROL under FUEL SYSTEM.
- Fuel Pump Control - See FUEL DELIVERY under FUEL SYSTEM.
- Idle Air Adjusting Unit - See IDLE SPEED under FUEL SYSTEM.
- Idle Speed Control Valve - See IDLE SPEED under FUEL SYSTEM.
- Pressure Regulator Control Solenoid Valve - See FUEL DELIVERY under FUEL SYSTEM.
- Self-Diagnostics - See SELF-DIAGNOSTICS SYSTEMS.
- Torque Converter Lockup - See MISCELLANEOUS CONTROLS.
- Wastegate Solenoid - See AIR INDUCTION SYSTEM.
FUEL SYSTEM
The fuel system is controlled by ECA, based on data received from EEC system. The ECA monitors engine operating conditions based on input received from engine switches and sensors. Control of output actuators determines fuel mixture and idle speed. On vehicles with turbocharger, the ECA also controls the ignition output signal.
Fuel Pump
Fuel is supplied by in-tank electric fuel pump. Pump delivers fuel from fuel tank, through 20-micron fuel filter, to fuel charging manifold assembly. Fuel charging manifold assembly incorporates electrically actuated fuel injectors directly above each intake port. Injectors spray metered quantity of fuel into intake air. Constant fuel pressure is maintained to injector nozzles by pressure regulator.
Fuel Pump Relay
When ignition switch is turned to ON position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and to timer in ECA. Fuel pump receives power through fuel pump relay contacts.
If ignition switch is not turned to START position, timer in ECA will open ground circuit after approximately one second. ECC senses engine speed; when engine stops, or when engine speed drops to less than 120 RPM, ECC shuts off fuel pump by opening ground circuit to fuel pump relay.
Opening ground circuit de-energizes fuel pump relay (contacts opened) and de-energizes fuel pump. This allows pressurization of fuel system. When ignition switch is turned to START position, ECA operates fuel pump relay to provide fuel during cranking to start engine.
Fuel Pressure Regulator
Fuel pressure regulator is attached to fuel supply manifold assembly downstream of fuel injectors. Regulator is a diaphragm-operated relief valve, in which one side of diaphragm senses fuel pressure, and other side is subjected to intake manifold pressure. It regulates fuel pressure supplied to injectors.
Fuel pressure is controlled by spring preload applied to diaphragm. Balancing one side of diaphragm with manifold pressure will maintain constant fuel pressure at injectors. Excess fuel supplied by pump, but not consumed by engine, passes through regulator and returns to fuel tank through fuel return line.
Pressure Regulator Control (PRC) Solenoid (2.2L)
The PRC solenoid valve controls vacuum to fuel pressure regulator. When solenoid is de-energized, vacuum is supplied to pressure regulator. When solenoid is energized, vacuum is vented to the atmosphere. Solenoid is controlled by the ECA. It is mounted on firewall, next to canister purge regulator solenoid valve.
Fuel Pump Shut-Off (Inertia) Switch
The inertia switch is an electrical-interrupt switch in the fuel system. In the event of a collision or vehicle roll-over, electrical contacts within the inertia switch open, and fuel supply to the electric fuel pump is shut off. Fuel supply will be interrupted even if the engine is still running.
A reset button is located on the switch assembly. If the electrical circuit trips, it is not possible to re-start vehicle unless switch is reset by depressing reset button. Anytime the switch opens, fuel system should be inspected for damage before resetting.
| CAUTION | DO NOT reset inertia switch until complete fuel system has been inspected for leaks. |
Fuel Injectors
The electronic fuel injection system is a pulse time, PFI system. The ECA controls fuel injectors to meter fuel quantity into intake ports. The ECA receives inputs from engine sensors to compute fuel flow necessary to maintain air/fuel ratio throughout entire engine operational range. The on time of the injector is the only controlled variable in fuel delivery system. The ECA controls the length of time each injector is on, or energized.
Each cylinder has a solenoid-operated injector which sprays fuel toward back of each intake valve. Fuel injector nozzles are solenoid-operated valves which meter and atomize fuel delivered to engine. Each injector receives battery voltage through an ignition switch circuit. The ECA-controlled ground circuit is used to complete the circuit and energize (on time) the injector. The on time controls the amount of fuel delivered.
Injector bodies consist of solenoid-actuated pintle and needle valve assembly. Injector flow orifice is fixed, and fuel pressure at injector tip is constant. Fuel flow to engine is regulated by how long solenoid is energized. This length of time is known as pulse width. Atomization spray is obtained by shape of pintle.
By-Pass Air (BPA) Valve (1.8L)
The BPA valve increases cold idle RPM to speed engine warm up and prevent stalling. The BPA uses thermowax that expands or contracts according to the temperature of coolant circulating through the valve.
Idle Speed Control (ISC) Solenoid (1.8L)
The ISC receives signals from ECA, which control the ISC rotary valve to regulate air passage in the by-pass port. When the ISC valve is deactivated, the rotary valve will automatically shift to the half-opened position. This feature is designed as a limited operation strategy in case of ISC failure.
Idle Speed Control/By-Pass Air (ISC/BPA) Valve (2.2L)
The ISC/BPA controls idle speed by regulating throttle plate by-pass air. The valve consists of air by-pass valve which functions during cold engine conditions below 140°F (60°C), and idle speed control solenoid valve which works the entire temperature range.
The air by-pass valve is controlled by the engine coolant temperature. The idle speed control solenoid is controlled by the ECA. The ISC/BPA controls cold engine fast idle, no-touch starting, hot engine idle and engine idle load correction.
See ECA INPUT SENSORS under COMPUTERIZED ENGINE CONTROLS.
See ECA INPUT SENSORS under COMPUTERIZED ENGINE CONTROLS.
1.8L
The Electronic Spark Advance (ESA) system uses an ignition module, Crankshaft Position Sensor (CPS) and ECA to regulate ignition timing. Piston position and engine RPM are monitored by Crankshaft Position Sensor (CPS) and Cylinder Identification (CID) sensor.
The CPS creates 4 evenly spaced signal pulses as slots in the outer edge of the disc pass through it. These signals are used to control transistors in the ignition module to break the primary circuit in the ignition coil. The CPS also supplies the ECA with information for engine RPM and injector timing.
The CID sensor creates one signal pulse per distributor revolution as the inner slot of the disc passes through. This signal is sent to the ECA to identify No. 1 cylinder TDC (compression stroke) for calculation of injection timing.
2.2L
On non-turbo engines, a Hall effect electronic distributor with mechanical and vacuum advance is used. A reluctor, mounted on the distributor shaft, is used to trigger the Hall effect switch. When the reluctor tooth is aligned with the Hall effect device, a magnetic field is completed and the output signal will be low. When the reluctor tooth moves out of alignment with the Hall effect device, the field is shunted and the output signal will change from low to high.
On turbo engines, an Electronic Spark Advance (ESA) system with ECA-controlled timing is used. The ignition module, mounted to the side of the distributor, uses a 5-wire connector. The ECA connects to the ignition module through 2 wires, and the remaining 3 wires connect to the power relay, coil and ground circuit.
The ECA transmits spark timing signals to the ignition module. The ignition coil primary circuit is interrupted by this signal, and high voltage is created in the ignition coil secondary circuit.
The distributor houses the Crankshaft Position Sensor (CPS) and Cylinder Identification (CID) sensor. The CID is a 2-piece sensor. The first sensor detects No. 1 cylinder TDC, and the other sensor detects No. 4 cylinder TDC. The ECA uses these signals to adjust ignition and fuel injection timing.
The CPS monitors the 24 teeth on the distributor rotor. An electrical signal is generated as each rotor tooth passes the CPS. These signals are used by the ECA to determine engine RPM.
The Ignition Diagnostic Monitor (IDM), used on all models, is an output from the ignition module which provides ignition diagnostic information to the ECA for self-test. If the CID circuit fails and an attempt to start the engine is made, the ignition module will randomly select a firing order. If hard starting results, turning the ignition off and then cranking again will result in another "guess". Several attempts may be needed until the proper firing order is selected, allowing the vehicle to be started and driven until repairs can be made. The Limited Operation Strategy (LOS) system attempts to keep the vehicle driveable in spite of the system failures preventing ECA from providing spark angle or dwell commands.
VACUUM CONTROL VALVES (VCV)
Temperature-operated vacuum switches have 2 or more ports. They use wax pellet or bimetallic material to either open or close vacuum ports when normal engine operating temperature is reached. Valves are mounted in some part of cooling system so that the base is immersed in coolant.
Vacuum Delay Valves
Valves are inserted in vacuum lines to provide gradual application or release of vacuum to engine or emission control devices. Valves may be one way or two ways, depending on function and part of system affected.
Vacuum Reservoir
The vacuum reservoir stores vacuum to provide a consistent vacuum signal. It prevents rapid fluctuations or sudden drops in a vacuum signal, such as that seen during acceleration.
Vacuum Restrictor
This orifice-type flow restrictor is used in several emission calibrations to control flow rate and/or actuation timing of components and systems.
Vacuum Vent Valves
Valve controls induction of fresh air into system to prevent accumulation of fuel vapors, which could cause decay of vacuum diaphragms. Valve may be vent valve only, or combined vent and delay valve. Valves should always be mounted so ports point downward.
EGR SYSTEM COMPONENTS
Note. Exhaust Gas Recirculation (EGR) is not used on 1.8L engines.
Exhaust Gas Recirculation (EGR) Valve
The EGR system allows blending of exhaust gas into the intake mixture. This lowers combustion temperatures due to lower concentrations of oxygen. Lowering of combustion temperatures reduces amount of Oxides of Nitrogen (NOx) emissions.
Turbocharged engines use electronic EGR valve. EGR flow is controlled according to ECA demands, by means of an EGR Valve Position (EVP) sensor attached to the valve. The EGR valve is operated by a vacuum signal from EGR control solenoid valve.
Non-turbocharged engine incorporates a modified ported EGR valve and a remote backpressure transducer. The vacuum applied to EGR valve is modulated by sensing exhaust backpressure and bleeding off some vacuum when backpressure is low. This provides EGR flow that is proportional to engine load. Vacuum supplied to EGR transducer is controlled by an EGR control solenoid valve.
EGR Backpressure Variable Transducer (2.2L Non-turbo)
The EGR backpressure variable transducer converts engine vacuum and exhaust backpressure into a vacuum signal that controls the EGR valve.
When exhaust backpressure is low (engine cold, less than 1500 RPM), the transducer will vent vacuum to atmosphere and EGR valve will close. When engine is warm and RPM is in cruise range, the transducer will close or modulate near closed position, and allow ported vacuum to open EGR valve.
EGR Control Solenoid Valve
Non-turbocharged engines use a single EGR control solenoid. The solenoid supplies vacuum to EGR valve when de-energized, and vents vacuum through its air filter when energized. It also receives a signal from the ECA according to EGR requirements. Both turbocharged and non-turbocharged EGR solenoid valves are mounted on the firewall.
The turbocharged engine uses a dual-type EGR control solenoid. One is a vacuum vent valve which supplies vacuum to EGR valve when energized. The second valve is a vent valve which vents EGR valve to the atmosphere when de-energized. Both solenoid valves receive variable duty cycle signals from ECA according to EGR requirements.
EGR Vent (EGRV) Solenoid (2.2L Turbo)
Solenoid vents EGR control solenoid vacuum line. Valve is normally open, and vacuum is not supplied to EGR valve. When energized, vacuum is supplied to EGR valve.
This sensor is attached to EGR valve assembly and indicates position of EGR valve to EEC system. The EVP sensor also has the ability to signal the ECA in the event of EGR circuit failure. Sensor is located on top of EGR valve.
Canister Purge (CANP) Solenoid Valve
The CANP controls the amount of vapors drawn from carbon canister into the intake plenum. The ECA uses various inputs from sensors to determine calibration of vapor transfer.
When signaled by the ECA, CANP solenoid opens the passage between the carbon canister and the intake plenum. When de-energized, vacuum line to the purge valve is vented to the atmosphere. Carbon canister is purged by drawing vapors into air cleaner.
Carbon Canister
Carbon canister storage is used for evaporative fuel control on all vehicles. The evaporative emission control system stores gasoline fumes from fuel tank in a carbon canister, until fumes can be drawn into engine for burning during combustion process.
There are 4 basic components used in the evaporative emission control system
- Activated Carbon Canister
- Vacuum-Operated Canister Control Valve
- Computer-Controlled Solenoid
- Tank Pressure Control Valve
For specific component application and vacuum hose routing, see appropriate VACUUM DIAGRAMS article in this section.
Canister Purge Solenoid Valve
Valve is normally closed; it regulates flow of fuel vapors from canister to intake manifold. Valve is controlled by a signal from the ECA during various engine operating modes.
Fill Control/Vent System
Fill limiting is accomplished through configuration of fill neck and/or internal vent lines within fill neck and tank. Vent system is designed to permit air space in 10-12 percent of tank when tank is filled to capacity. Air space allows for thermal expansion of fuel, and provides aid to in-tank vapor vent system.
Purge Control Solenoid Valve
See CANISTER PURGE SOLENOID VALVE above.
Pressure/Vacuum Relief Fuel Cap
This system consists of a sealed filler cap with integral pressure/vacuum relief valve. Fuel system vacuum relief is provided after 1.0 in. Hg of vacuum; pressure relief is provided after 1.8 psi. (.13 kg/cm 2 ). Under normal conditions, fill cap allows air to enter fuel tank as fuel is used while preventing vapors from escaping.
Rollover Vent Valve (2.2L)
This valve releases excessive fuel tank pressure to atmosphere. If vehicle is rolled over, valve will prevent fuel tank drainage through evaporative hoses. Rollover vent valve is located inside the vapor separator.
Vacuum Check Valve
A vacuum check valve blocks airflow in one direction. It allows free airflow in the other direction.
Vapor Separator
The vapor separator allows vapor to vent to the carbon canister while holding fluid in fuel tank. Vapors are routed through a single vapor line to carbon canister in engine compartment.
The vapor separator is located between fuel tank and evaporative lines to carbon canister. Venting fuel vapor prevents engine surging from fuel enrichment, and assists in hydrocarbon emission control.
POSITIVE CRANKCASE VENTILATION (PCV)
The PCV system uses intake manifold vacuum to eliminate blow-by vapors from crankcase. The mixture is then passed into the combustion chamber and burned. PCV valve provides control by metering flow of blow-by vapors according to manifold vacuum.
Under conditions where abnormal amounts of blow-by gases are produced (such as worn cylinders or rings), the system is designed to allow excess gases to flow back through crankcase vent hose, into air inlet for consumption on during normal combustion.
SELF-DIAGNOSTIC SYSTEMS
Note. All systems have self-diagnostic capabilities. For procedures on entering self-test modes and reading service codes, see the appropriate TESTS W/CODES article in this section.
CHECK ENGINE LIGHT
The CHECK ENGINE light (if equipped) will illuminate when ignition is turned to the ON position (bulb check), or when systems related to the EEC system malfunction during normal engine operation. For additional information, see the appropriate TESTS W/CODES article in this section.
A/C CLUTCH CYCLING PRESSURE SWITCH
On models with manual A/C system, the A/C clutch cycling pressure switch is mounted on top of the receiver-drier. Based on refrigerant system pressure, a signal is sent to the ECA. ECA uses this signal to maintain system pressure within the programmed range.
COOLING FAN
The ECA regulates operation of the electric cooling fan through an ECA-controlled relay which controls the ground circuit or power circuit for the cooling fan. This allows ECA to operate cooling fan based on engine temperature. A malfunction of the cooling fan will cause engine overheating and possible detonation.
Torque Converter Lockup
The purpose of the transaxle torque converter lockup feature is to eliminate power loss of torque converter stage, when vehicle is in cruise condition. This allows convenience on automatic transaxle, and fuel economy on manual transmission.
Converter clutch will engage under the following conditions: vehicle is moving faster than a precalibrated speed, engine is at normal operating temperature, throttle position sensor output is not changing (indicating a steady road speed), transaxle in high gear and brake switch closed.
When vehicle speed is great enough, the 4-speed Electronic Automatic Transaxle (4EAT) control module energizes converter clutch solenoid mounted in transmission. This allows torque converter to directly connect engine to transmission. When operating conditions indicate transmission should operate as normal, converter clutch solenoid is de-energized. This allows transmission to return to normal automatic operation.