All models are equipped with a crankcase emission reduction system, as well as the following systems, depending on the model:
Models with a 1.6 liter carbureted engine without a catalytic converter - an exhaust emission control system when the engine is idling and a throttle damper.
1.6L Carburetor Engine Models with Catalytic Converter - Catalytic Converter, Exhaust Gas Recirculation System, Evaporative Emission Control System, Air Intake System, Idle Emission Control System, and Throttle Damper.
Models with a 1.6-liter engine and multi-point fuel injection system - a catalytic converter, an exhaust gas recirculation system and a fuel vapor control system from the fuel system.
Models with a 2.0 liter engine and a single point fuel injection system without a catalytic converter - a thermal aftertreatment system for exhaust gases and a throttle damper.
Models with a 2.0 liter engine and a single point fuel injection system with a catalytic converter - catalytic converter, exhaust gas recirculation system, fuel vapor control system, thermal exhaust aftertreatment system and throttle damper.
Models with a 2.0 liter engine and multipoint fuel injection system without a catalytic converter - no additional emission control systems are installed.
Models "Phase I" (release before June 1993) with a 2.0-liter engine and a multi-point fuel injection system with a catalytic converter - a catalytic converter and a fuel vapor control system from the fuel system.
Models "Phase II" (release after June 1993) with a 2.0-liter engine and a multipoint fuel injection system with a catalytic converter - a catalytic converter, a fuel vapor control system from the fuel system and an exhaust gas recirculation system.
Crankcase emission reduction system
To reduce the release of unburned hydrocarbons from the engine crankcase into the atmosphere, the engine is hermetically sealed, and the gases and engine oil vapors escaping into the engine crankcase are taken from the crankcase through the valve into the inlet channel, from where they will then enter the engine and be burned in the following engine operation cycles.
If there is a very low vacuum in the intake manifold, the gases will simply be drawn into it from the crankcase. When the vacuum in the intake manifold is not so large, the gases will exit the engine crankcase under the influence of a higher (relatively) crankcase pressure; when the engine is worn out, increased crankcase pressure (due to increased gas breakthrough) will cause some of the gases to flow into the intake manifold at any pressure in the manifold.
Catalytic converter
To reduce the amount of harmful substances entering the atmosphere, on some models, a catalytic converter is installed in the exhaust system. All models equipped with a catalytic converter use a closed loop control system. In this system, the exhaust gas sensor constantly informs the engine's electronic control unit about the oxygen content in the exhaust gases. This allows the electronic control unit to regulate the composition of the fuel mixture so that the catalytic converter works at maximum efficiency.
The sensor is sensitive to the oxygen content in the exhaust gases and sends signals to the electronic control unit with different voltages depending on its concentration. If the intake air/fuel mixture is too rich, the sensor sends out a high voltage signal. The voltage decreases as the oxygen content in the fuel mixture increases. The maximum exhaust gas neutralization ratio of the catalytic converter is achieved when the chemically correct composition of the fuel mixture / intake air for complete combustion of gasoline is maintained - 14.7 parts (by weight) air to 1 part fuel (stoichiometric ratio). With this ratio, the voltage of the sensor signals changes dramatically and the electronic control unit accordingly regulates the composition of the fuel mixture / intake air, changing the duration of the injector pulse (ov) (time during which the injector is open). On later models, the sensor has a built-in heating element (controlled by an electronic control unit), which serves to quickly warm up the sensitive tip of the sensor to normal operating temperature.
Control system for the release of fuel vapors from the fuel system
To minimize emissions of unburned hydrocarbons into the atmosphere, models with a catalytic converter are equipped with a system to control the release of fuel vapors from the fuel system. The fuel filler cap is hermetically sealed and the carbon filter collects gasoline vapors formed in the fuel tank (fuel injected models) or in the fuel tank and carburetor float chamber (models with carburetor engine), when the vehicle is stationary. Vapors remain in the charcoal filter until they can be released into the intake port when the engine is running.
On models with a carbureted engine, the system is controlled by a thermal vacuum valve, which is installed in the intake manifold; the thermal vacuum valve also controls the operation of the exhaust gas recirculation system. When the engine is cold, the thermal vacuum valve closes the vacuum supply to the carbon filter vacuum diaphragm valve and the filter remains closed. When the engine warms up to normal operating temperature (about 70°C), the thermal vacuum valve opens and the vacuum present in the intake manifold acts on the carbon filter diaphragm. The membrane valve opens and all the vapors collected in the carbon filter are drawn into the intake duct with subsequent combustion in the following engine cycles.
On models "Phase I" (release before June 1993) with a 2.0 liter engine and multi-port fuel injection system, the carbon filter is connected directly to the intake manifold and the system is controlled by a restrictor valve on the filter's vacuum diaphragm valve. When the engine is running, the vacuum present in the intake manifold acts on the diaphragm through the restrictor valve. When the engine is running at idle, the valve is closed, but as the engine speed increases, the vacuum in the intake manifold increases. The restrictor valve increases the vacuum behind the diaphragm, thus controlling the opening of the diaphragm valve depending on the engine speed. The valve is slightly open when the engine speed is low, but opens fully when the engine speed is increased.
On all models with fuel injection, the operation of the fuel vapor control system from the fuel system is controlled by the engine's electronic control unit through a solenoid valve; the same solenoid valve controls the operation of the exhaust gas recirculation system. In order for the engine to operate correctly after a cold start and/or at idle, and to protect the catalytic converter if the engine is too rich, the solenoid valve is not opened by the ECM until the engine is warmed up or load will be given. After that, the solenoid valve opens so that the collected fuel vapors can enter the intake port.
Exhaust gas recirculation system
This system reduces the content of unburned hydrocarbons in the exhaust gases before they enter the catalytic converter. To do this, some of the exhaust gases are taken from the exhaust manifold and released back into the intake manifold through a pipe connecting them, after which they again participate in the engine. The EGR valve is installed at the end of the connecting tube that attaches to the intake manifold.
On models with a carburetor engine, the system is controlled by a thermal vacuum valve and a back pressure valve. The thermal vacuum valve also controls the operation of the fuel vapor control system from the fuel system. When the engine is cold, the thermal vacuum valve stops the vacuum flow to the recirculation valve, and it remains closed. When the engine is warmed up to normal operating temperature (about 70°C), the thermal vacuum valve opens, allowing vacuum to act on the recirculation valve through the backpressure valve. The backpressure valve is sensitive to the exhaust gas pressure and, in accordance with it, opens or closes the recirculation valve. When exhaust pressure is high, the backpressure valve is closed, allowing vacuum to act on the recirculation valve, opening it. When the exhaust gas pressure drops, the backpressure valve opens, stopping the vacuum flow to the recirculation valve, the valve closes.
On fuel-injected models, the exhaust gas recirculation system is controlled by the ECM via a solenoid valve and a backpressure valve; the solenoid valve also controls the operation of the fuel vapor control system from the fuel system. When the engine is cold, the ECM keeps the solenoid valve closed, cutting off vacuum from the recirculation valve. When the engine warms up to normal operating temperature, the ECM opens the solenoid valve, allowing vacuum to act on the recirculation valve through the backpressure valve. The backpressure valve is sensitive to the exhaust gas pressure and, in accordance with it, opens or closes the recirculation valve. When exhaust pressure is high, the backpressure valve is closed, allowing vacuum to act on the recirculation valve, opening it. When the exhaust gas pressure drops, the backpressure valve opens, stopping the vacuum flow to the recirculation valve, the valve closes.
Exhaust gas aftertreatment system
This system reduces the content of unburned hydrocarbons in the exhaust gases, preventing their excessive entry into the exhaust gases. This is achieved by supplying additional air to the intake manifold when the vacuum in the intake manifold is very high. The system includes only one valve.
The exhaust gas aftertreatment valve is sensitive to intake manifold pressure. If there is too much vacuum in the intake manifold (those. when the throttle is closed at high engine speed), the valve opens and lets in a portion of fresh filtered air from the air filter housing into the intake manifold.
Exhaust air intake system
Exhaust manifold air intake system reduces unburned hydrocarbons (HC) and carbon dioxide (SO) in the exhaust gases by passing part of the air filtered by the air filter directly into the exhaust manifold so that a significant part of the molecules of unburned hydrocarbons and carbon dioxide can be oxidized in the exhaust manifold before entering the catalytic converter. The system includes an air supply valve and a solenoid valve controlled by an electronic engine control unit.
In order for the engine to operate correctly after a cold start and/or at idle, the solenoid valve is not opened by the ECU until the engine is warmed up and a load is applied to it. When both of these conditions occur, the solenoid valve opens so that a portion of fresh air filtered by the air filter can enter the exhaust manifold. The air filter draws air from the pressure difference between the exhaust manifold and the air filter, so there is no need to use an air pump to supply air. The air inlet valve only allows air to flow in one direction, so exhaust gases cannot enter the air filter.
Emission control system when the engine is idling
The idling exhaust emission control system ensures that the fuel mixture does not become too rich when the engine temperature is high. This is achieved by letting more air into the intake manifold when the engine temperature is high. The system includes only one valve, which is installed on the air filter housing.
The idle emission control valve has a temperature sensitive bimetal spring. When the engine temperature is low, the valve is closed. When the temperature in the air filter housing rises, the valve's bimetal spring deforms and the valve gradually opens. This allows fresh air, filtered by the air filter, to enter the intake manifold, which increases the oxygen content in the fuel mixture.
Throttle damper
The throttle damper is used to reduce the content of unburned hydrocarbons in the exhaust gases when the engine is turned off or a sharp decrease in speed. This is achieved by preventing abrupt closing of the throttle, for example, when the driver quickly releases the accelerator pedal at high engine speeds. The throttle damper serves as a shock absorber and closes the throttle slowly in the final stages. This reduces the content of unburned hydrocarbons in the exhaust gases, preventing too much vacuum in the intake manifold, which would lead to unburned fuel entering the exhaust manifold.
Crankcase emission reduction system
This system requires no maintenance other than checking the condition of the hoses and changing the filter (if installed) at regular intervals (see subsection 2.2.7 and subsection 2.4.1).