DESCRIPTION & OPERATION
Vehicles utilize several types of devices to control emissions. Although originally intended for a specific purpose, many of the devices are now used in various parts of the system. These figures show the physical appearance of typical components and their identification symbols found on Emission Control Diagrams. Operation and method of actuation is provided for most devices. Refer to specific system within this section for testing procedures.
A/C-WOT MICROSWITCH
Switch is mounted on carburetor to sense Wide Open Throttle (WOT) position. On some applications, an adjusting screw is mounted on a lever that rotates with the throttle lever. As lever is rotated to WOT position, it contacts arm of microswitch that opens or closes an electrical circuit. On other applications, the adjusting screw can be set to any predetermined throttle angle before the WOT position. The switch is used on most carbureted models and cuts out the A/C compressor during WOT acceleration.
A/C-WOT Microswitch. Scheme 1
AIR BY-PASS VALVE
Vacuum operated valves may be normally open or closed. Valves direct airflow from thermactor air pump to exhaust system or atmosphere as required. May be mounted on air pump or in-line (remote).
Normally closed valves supply air to the exhaust system with medium and high applied vacuum signals during normal modes, short idles and some acceleration. With low or no vacuum applied the pump air is dumped through the silencer ports of the valve. Normally open valves with a vacuum vent provide a timed air dump during decelerations and also dump when a vacuum pressure difference is maintained between the signal port and the vent port.
Air By-Pass Valve. Scheme 2
AIR CHARGE TEMPERATURE (ACT) SENSOR
The ACT is threaded into the intake manifold or air cleaner. Senses air/fuel mixture temperature and provides instant information to EFI system. The ACT is also used as a density corrector for airflow calculation and to proportion the cold enrichment fuel flow.
Air Charge Temperature (ACT) Sensor. Scheme 3
AIR CHECK VALVE & PULSE AIR VALVE
One-way valve allows thermactor air to enter exhaust system while preventing exhaust gases from passing in the opposite direction. Pulse air valve is not interchangeable with air check valve.
Air Check Valve & Pulse Air Valve. Scheme 4
AIR CLEANER COLD WEATHER MODULATOR
A cold weather modulator is sometimes used in addition to the air cleaner temperature control sensor to control the inlet air temperature. The cold weather modulator traps vacuum in the system, so air control door will not switch to cold air when vacuum drops during acceleration. The cold weather modulator only works when the outside air is cold.
Air Cleaner Cold Weather Modulator. Scheme 5
AIR CLEANER TEMPERATURE SENSOR
This sensor is installed in the lower air cleaner tray and is subject to temperature changes within the air cleaner. At a given increase in temperature, the sensor bleeds off vacuum to the air cleaner air control door, permitting the vacuum motor to open the duct door and allow fresh air in while shutting off full heat.
Air Cleaner Temperature Sensor. Scheme 6
AIR CLEANER VACUUM MOTOR
Regulates position of air control door within air cleaner duct to allow warm or cold air in as signaled by the air cleaner temperature sensor and cold weather modulator.
Air Cleaner Vacuum Motor. Scheme 7
AIR SILENCER
The air silencer is a combination silencer and filter for air supply pumps that are not equipped with an impeller type centrifugal air filter fan or for pulse air (thermactor II) systems. The air silencer is mounted in a convenient position in the engine compartment and is connected to the air supply pump or pulse air valve inlet by means of a flexible hose.
Air Silencer. Scheme 8
AIR SUPPLY CONTROL VALVES
Operated by vacuum to direct air pump output to exhaust manifold or downstream to catalyst system depending on system requirements.
ANTI-BACKFIRE (GULP) VALVE
Vacuum operated valve downstream from air by-pass valve. Used to divert partial thermactor air to intake manifold when triggered by intake manifold vacuum during sudden deceleration.
Anti-Backfire (Gulp) Valve. Scheme 9
CANISTER PURGE SOLENOID
Normally closed solenoid valve controls the flow of fuel vapors from canister to intake manifold. Opened or closed by a signal from the electronic control assembly during various engine operating modes.
Canister Purge Solenoid. Scheme 10
CANISTER PURGE VALVE
Vacuum operated purge valve controls flow of fuel vapors from carbon canister to engine.
Canister Purge Valve. Scheme 11
CARBON CANISTER
Fuel vapors from fuel tank and carburetor bowl are stored in a carbon canister until the vehicle is operated, at which time, the vapors will purge from the canister into the engine for consumption. There are 2 canister sizes. In some applications dual canisters are used on vehicles with large fuel tanks.
Carbon Canister. Scheme 12
CARBURETOR FUEL BOWL SOLENOID VENT VALVE
A normally open valve is located in the fuel bowl vent line. The vent valve closes off the fuel bowl vent line when the engine is running and returns to normally open position when ignition is turned off.
Carburetor Fuel Bowl Solenoid Vent Valve. Scheme 13
CARBURETOR FUEL BOWL THERMAL VENT VALVE
Inserted in carburetor-to-canister vent line, valve is closed when engine compartment is cold. This prevents fuel tank vapors, generated when fuel tank heats up before engine compartment does, from being vented through carburetor fuel bowl.
Carburetor Fuel Bowl Thermal Vent Valve. Scheme 14
COMBINATION AIR BY-PASS & AIR CONTROL VALVE
The combination air by-pass and air control valve combines the functions of the by-pass valve and the air control valve into a single unit. There are 2 normally closed valves, the non-bleed type and the bleed type all of which look alike. One distinguishing feature will be that the bleed type will have the percent of bleed molded into the plastic case.
Combination Air By-Pass & Air Control Valve. Scheme 15
DUAL THERMACTOR AIR CONTROL SOLENOID VALVE
The dual thermactor air control solenoid valve assembly consists of 2 closed solenoid valves, one controlling the thermactor air by-pass valve and the other the thermactor diverter valve. Both are vented when de-energized, sourced by the intake manifold vacuum reservoir and controlled by the EEC system.
EGR BACKPRESSURE VARIABLE TRANSDUCER
A vacuum bleed hole, located inside the transducer, vents EGR vacuum to the atmosphere until sufficient exhaust backpressure is applied closing the bleed hole. When this happens, vacuum is then routed to the EGR and normal operation begins.
EGR Backpressure Variable Transducer. Scheme 16
EGR COOLER
This is a heat exchanger that uses engine coolant to reduce EGR gas temperatures in EEC applications only.
EGR Cooler. Scheme 17
EGR SOLENOID VACUUM VALVE ASSEMBLY
The dual EGR solenoid valve assembly consists of 2 dithering solenoid valves. One is a vacuum vent valve which supplies vacuum to the EGR when energized. The second valve is a vent valve which vents the EGR valve to the atmosphere when de-energized. Both solenoid valves receive variable duty cycle signals from the ECU according to EGR requirements.
EGR Solenoid Vacuum Valve Assembly. Scheme 18
EGR VACUUM LOAD CONTROL (WOT) VALVE
Operated by vacuum signal from carburetor venturi port. At or near wide open throttle (WOT), the valve interrupts vacuum to EGR valve.
EGR Vacuum Load Control (WOT) Valve. Scheme 19
EGR VALVE & TRANSDUCER ASSEMBLY
The valve and transducer assembly which consists of a modified ported EGR valve and a remote transducer, is used on selected 2.0L and 2.3L engines. This assembly works the same as the integral backpressure transducer EGR valve and is diagnosed and serviced as an assembly only. Valve functional checks are the same as those for the integral backpressure transducer EGR valve.
EGR Valve & Transducer Assembly. Scheme 20
EGR VALVE-ELECTRONIC
The electronic EGR valve is required in EEC systems where EGR flow is controlled according to computer demands of an EGR valve position sensor attached to the valve. The valve is operated by a vacuum signal from the dual EGR solenoid valves or the electronic vacuum regulator which actuates the valve diaphragm.
EGR Valve-Electronic. Scheme 21
EGR VALVE-INTEGRAL BACKPRESSURE TRANSDUCER
The integral backpressure transducer EGR valve combines inputs of exhaust backpressure and EGR port vacuum into one unit. The valve requires both inputs to function. The valve will not function on vacuum alone. This backpressure valve is available in 2 types, poppet and tapered pintle.
EGR Valve-Integral Backpressure Transducer. Scheme 22
EGR VALVE-PORTED
The ported EGR valve is operated by a vacuum signal from the carburetor EGR port signal which actuates the valve diaphragm. As the vacuum increases sufficiently to overcome the power spring, the valve is opened allowing EGR flow. The amount of flow is dependent on tapered pintle or poppet position which is a direct result of the vacuum signal.
EGR VALVE POSITION (EVP) SENSOR
Attached to the EGR valve assembly, this sensor indicates position of EGR valve to the EEC.
EGR Valve Position (EVP) Sensor. Scheme 23
EGR VENTURI VACUUM AMPLIFIER (VVA)
This amplifier uses a relatively weak vacuum signal from the carburetor venturi to control EGR valve. Contains a check valve and a relief valve that opens whenever the venturi vacuum signal is equal to or greater than manifold vacuum.
EGR Venturi Vacuum Amplifier (VVA). Scheme 24
EXHAUST HEAT CONTROL VALVE
Used to divert hot gases from exhaust manifold to intake manifold riser pad to heat the incoming air/fuel charge. Two types are used, a bimetal spring type and a vacuum actuated type.
Exhaust Heat Control Valve. Scheme 25
FEEDBACK CARBURETOR ACTUATOR MOTOR
Used on 7200 model carburetors, the actuator motor is threaded into carburetor body. Its actuator shaft moves a fuel metering pintle valve to produce a leaner/richer air/fuel mixture. Actuator shaft moves in response to signals from oxygen sensor and EEC or MCU system.
Feedback Carburetor Actuator Motor. Scheme 26
FUEL EVAPORATION HEATER SWITCH
The fuel evaporation heater (EFE) switch is mounted upside down at the rear of the engine on the bottom of intake manifold. The purpose of this switch is to control a relay and heater element in the early fuel evaporation system (EFE) based on engine temperature. The normally closed switch will activate the relay and heater at low engine temperature and will open at the specified calibration temperature of the switch. This will open the control relay shutting off the EFE heater after engine warm-up.
Fuel Evaporation Heater Switch. Scheme 27
HOT IDLE COMPENSATOR
The hot idle compensator is used to cool the engine during extreme hot engine idle operation. When open, the compensator bleeds air into the intake manifold, which leans out the air-fuel ratio at idle. The increased air intake causes an increase in engine idle speed, which results in cooling of the engine.
Hot Idle Compensator. Scheme 28
MICROPROCESSOR CONTROL UNIT (MCU)
Microprocessor-based module is programmed to interface with various types of sensors, switches and actuators to perform engine and emission control functions.
Microprocessor Control Unit (MCU). Scheme 29
OPEN LOOP SWITCH
The vacuum switch is a normally-open or normally-closed, vacuum-operated electric switch.
Open Loop Switch. Scheme 30
OXYGEN SENSOR (HEATED)
The oxygen sensor supplies the ECA with a signal which indicates either a rich or lean condition during engine operation.
Oxygen Sensor (Heated). Scheme 31
PRESSURE FEEDBACK ELECTRONIC EGR TRANSDUCER
The pressure feedback electronic EGR transducer converts a varying exhaust pressure signal into a proportional analog voltage which is digitized by the EEC IV processor. The processor uses this signal received from the transducer to compute the optimum EGR flow.
Pressure Feedback Electronic EGR Transducer. Scheme 32
TEMPERATURE COMPENSATED ACCELERATOR PUMP
The temperature compensated accelerator pump will allow delivery of a large pump capacity to facilitate cold engine requirements and a smaller pump capacity during warm engine operation. The amount of fuel delivered during warm engine operation is a function of the rate at which the accelerator pedal is opened. The design incorporates a by-pass bleed controlled by a vacuum operated valve. The input signal controlling the valve position is manifold vacuum switched by a temperature vacuum switch located in the engine coolant system.
Temperature Compensated Accelerator Pump. Scheme 33
TEMPERATURE VACUUM SWITCH (TVS)
The TVS incorporates a bimetal disc to open or close vacuum ports, and may be used in conjunction with the distributor, canister purge or EGR systems.
Temperature Vacuum Switch (TVS). Scheme 34
THERMACTOR IDLE VACUUM VALVE (TIV)
Prevents excessive underbody temperature of exhaust system by diverting secondary air pump output during extended engine idle. This valve also cuts EGR operation during heavy turbo boost modes.
Thermactor Idle Vacuum Valve (TIV). Scheme 35
VACUUM BOWL VENT VALVE & VACUUM/THERMOSTATIC BOWL VENT VALVE
The vacuum bowl vent valve and the vacuum/thermostatic bowl vent valve are vacuum and vacuum/temperature actuated on/off valves. The vacuum bowl vent valve and the vacuum thermostatic bowl vent valve are similar in appearance. The valves are used in the evaporative emission system to control vapor flow from the carburetor bowl to the carbon canister. With either valve, the flow path from the bowl to the canister is closed by manifold vacuum when the engine is running. The thermostatic valve also closes the bowl-to-canister flow path when the temperature of the valve is 90°F (32°C) or less (even without manifold vacuum). When the temperature of the valve is 120°F (49°C) or more, the valve is open (unless closed by manifold vacuum).
Vacuum Bowl Vent Valve & Vacuum/Thermostatic Bowl Vent Valve. Scheme 36
VACUUM CHECK VALVE
Vacuum check valves block airflow in one direction and allow free airflow in the other direction.
Vacuum Check Valve. Scheme 37
VACUUM CONTROL
Temperature operated vacuum switches have 2 or more ports. They utilize wax pellet or bimetal material to either open or close the vacuum ports. Normally mounted in some part of cooling system so that the base is immersed in coolant. May be normally open or normally closed. One version includes an electrical vacuum switch on its top.
Vacuum Control. Scheme 38
VACUUM DELAY VALVES
Inserted in vacuum lines to provide for gradual application or release of vacuum to engine or emission control devices. May be one or 2 way valves, depending on function and part of system affected.
Vacuum Delay Valves. Scheme 39
VACUUM VENT VALVES
Controls induction of fresh air into system to prevent accumulation of fuel vapors which could cause decay of vacuum diaphragms. May be vent valve only or combined vent and delay valve. Valves should always be mounted so ports point downward.
Vacuum Vent Valves. Scheme 40
WIDE OPEN THROTTLE VALVE
This valve dumps EGR vacuum at or near wide open throttle.
Wide Open Throttle Valve. Scheme 41
EMISSION APPLICATIONS
Note. Applications information not included in this article. See the EMISSIONS APPLICATIONS article in this section.
COMPONENT TESTING
Note. Testing information not available.