Table of contents: Crankcase Emission Reduction System ↓ Catalytic converter ↓ Fuel vapor emission control system ↓ Exhaust gas recirculation system ↓ Thermal exhaust gas neutralization…↓ Exhaust manifold air intake system ↓ System for reducing exhaust toxicity…↓ Throttle Damper ↓ Crankcase Emission Reduction System ↓
All Nissan Sunny models described in this manual are suitable for use with unleaded petrol and have systems that help minimise harmful emissions into the atmosphere.
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 carburettor engine without a catalytic converter - a system for reducing toxic emissions when the engine is idling and a throttle damper.
Models with a 1.6-liter carburetor engine with a catalytic converter – a catalytic converter, an exhaust gas recirculation system, a fuel vapor control system from the fuel system, an air intake system, an exhaust toxicity reduction system when the engine is idling, and a throttle damper.
Models with a 1.6-liter engine and a multi-point fuel injection system - a catalytic converter, an exhaust gas recirculation system and a fuel vapor control system.
Models with 2.0-litre engine and single-point fuel injection system without catalytic converter – exhaust gas thermal neutralisation system and throttle damper.
Models with 2.0-liter engine and single-point fuel injection system with catalytic converter - catalytic converter, exhaust gas recirculation system, fuel vapor control system, exhaust gas thermal aftertreatment system and throttle damper.
Models with a 2.0-liter engine and a multi-point fuel injection system without a catalytic converter - no additional emission control systems are installed.
"Phase I" models (released 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 system for controlling the emission of fuel vapors from the fuel system.
"Phase II" models (released after June 1993) with a 2.0-liter engine and a multi-point fuel injection system with a catalytic converter - a catalytic converter, a fuel vapor control system and an exhaust gas recirculation system.
Crankcase Emission Reduction System
To reduce the emission of unburned hydrocarbons from the engine crankcase into the atmosphere, the engine is hermetically sealed, and gases and engine oil vapors breaking through into the engine crankcase are taken from the crankcase through a valve into the intake channel, from where they then enter the engine and will be burned in the following engine operating cycles.
If the vacuum in the intake manifold is very low, the gases will simply be drawn into it from the engine crankcase. When the vacuum in the intake manifold is not so high, the gases will be released from the engine crankcase under the influence of a higher (relatively) crankcase pressure; when the engine is worn out, the increased pressure in the crankcase (due to increased gas leakage) will force some of the gases to enter the intake manifold at any manifold pressure.
Catalytic converter
To reduce the amount of harmful substances released into the atmosphere, some models are equipped with a catalytic converter in the exhaust system. All models equipped with a catalytic converter use a closed-loop control system. In this system, the exhaust sensor continuously informs the engine control unit about the oxygen content of the exhaust gases. This allows the control unit to adjust the fuel mixture so that the catalytic converter operates with maximum efficiency.
The sensor is sensitive to the oxygen content in the exhaust gases and sends signals with different voltages to the electronic control unit depending on its concentration. If the intake air/fuel mixture is too rich, the sensor sends a high voltage signal. The voltage decreases as the oxygen content in the fuel mixture increases. The maximum efficiency 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) of air to 1 part of fuel (stoichiometric ratio). With this ratio, the voltage of the sensor signals changes sharply and the electronic control unit accordingly regulates the composition of the fuel mixture/intake air, changing the duration of the injector pulse (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.
Fuel vapor emission control system
To minimize emissions of unburned hydrocarbons into the atmosphere, models with a catalytic converter are equipped with a fuel vapor control system. The fuel filler cap is hermetically sealed and a carbon filter collects gasoline vapors formed in the fuel tank (fuel injection models) or in the fuel tank and carburetor float chamber (models with carburetor engine), when the car is stationary. The vapors remain in the carbon canister until they can be released into the intake duct when the engine is running.
On models with a carburetor 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 vacuum membrane valve of the carbon filter and the filter remains closed. When the engine warms up to normal operating temperature (approximately 70°C), the thermal vacuum valve opens and the vacuum present in the intake manifold acts on the diaphragm of the carbon filter. The membrane valve opens and all the vapors collected in the carbon filter are drawn into the intake channel and then burned in the next engine cycles.
On "Phase I" models (released before June 1993) with a 2.0 liter engine and a multi-point fuel injection system, the carbon canister is connected directly to the intake manifold and the system is controlled by a restrictor valve on the vacuum diaphragm valve of the filter. When the engine is running, the vacuum present in the intake manifold acts on the diaphragm through the restrictor valve. When the engine is idling, 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 at low engine speeds, but opens completely as the engine speed increases.
On all fuel-injected models, the fuel vapor control system is controlled by the engine control unit via a solenoid valve; the same electromagnetic valve controls the operation of the exhaust gas recirculation system. In order for the engine to run properly after a cold start and/or in idle mode, and to protect the catalytic converter when too rich a fuel mixture enters the engine, the electromagnetic valve is not opened by the electronic control unit until the engine is warmed up or under load. After this, the electromagnetic valve opens to allow the collected fuel vapors to enter the intake port.
Exhaust gas recirculation system
This system reduces the amount of unburned hydrocarbons in the exhaust gases before they reach 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 connecting tube, after which they are again used in the engine. The EGR valve is installed at the end of the connecting tube that is attached to the intake manifold.
On carbureted models, the system is controlled by a thermal vacuum valve and a backpressure valve. The thermal vacuum valve also controls the fuel vapor control system. When the engine is cold, the thermal vacuum valve stops the vacuum from reaching the EGR valve, and it remains closed. When the engine reaches normal operating temperature (approximately 70°C), the thermal vacuum valve opens, allowing the vacuum to act on the EGR valve through the backpressure valve. The backpressure valve is sensitive to exhaust pressure and opens or closes the EGR valve accordingly. When exhaust pressure is high, the backpressure valve is closed, allowing the vacuum to act on the EGR valve, opening it. When exhaust pressure drops, the backpressure valve opens, stopping the vacuum from reaching the EGR valve, and the valve closes.
On fuel-injected models, the exhaust gas recirculation system is controlled by the engine control unit via a solenoid valve and a backpressure valve; the solenoid valve also controls the operation of the fuel vapor control system. When the engine is cold, the ECM keeps the solenoid valve closed, cutting off the vacuum flow to the EGR valve. When the engine warms up to normal operating temperature, the ECM opens the solenoid valve, allowing the vacuum to act on the EGR valve through the backpressure valve. The backpressure valve is sensitive to the exhaust pressure and opens or closes the EGR valve accordingly. When the exhaust pressure is high, the backpressure valve is closed, allowing the vacuum to act on the EGR valve, opening it. When the exhaust pressure drops, the backpressure valve opens, cutting off the vacuum flow to the EGR valve, and the valve closes.
Thermal exhaust gas neutralization system
This system reduces the amount of unburned hydrocarbons in the exhaust gases by preventing them from entering the exhaust gases in excess. 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 thermal aftertreatment valve is sensitive to the pressure in the intake manifold. If too much vacuum is created in the intake manifold (i.e. when the throttle valve is closed at high engine speed), the valve opens and allows a portion of fresh filtered air from the air filter housing into the intake manifold.
Exhaust manifold air intake system
The air intake system reduces the amount of unburned hydrocarbons (HC) and carbon dioxide (CO) in the exhaust gases by passing a portion of the air filtered by the air filter directly into the exhaust manifold so that a significant portion of the unburned hydrocarbon and carbon dioxide molecules can be oxidized in the exhaust manifold before entering the catalytic converter. The system includes an air intake valve and a solenoid valve controlled by the electronic engine control unit.
In order for the engine to run properly after a cold start and/or at idle, the solenoid valve is not opened by the ECU until the engine is warm and under load. When both of these conditions occur, the solenoid valve opens to allow a portion of fresh air, filtered by the air filter, to enter the exhaust manifold. The difference in pressure between the exhaust manifold and the air filter is used to draw air from the air filter, so there is no need to use an air pump to supply air. The air inlet valve only allows air to pass in one direction, so exhaust gases cannot enter the air filter.
System for reducing exhaust toxicity when the engine is idling
The engine idle emission control system is designed to prevent the fuel mixture from becoming too rich at high engine temperatures. This is achieved by allowing additional air into the intake manifold at high engine temperatures. The system only includes one valve, which is mounted on the air cleaner housing.
The idle exhaust emission control valve has a temperature-sensitive bimetallic spring. When the engine temperature is low, the valve is closed. As the temperature in the air cleaner housing increases, the bimetallic spring of the valve 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 of the fuel mixture.
Throttle Damper
The throttle damper is designed to reduce the amount of unburned hydrocarbons in the exhaust gases when the engine is switched off or when the engine speed is suddenly reduced. This is achieved by preventing the throttle valve from closing abruptly, for example when the driver quickly releases the accelerator pedal at high engine speeds. The throttle damper acts as a shock absorber and slowly closes the throttle valve in the final stages. This reduces the amount of unburned hydrocarbons in the exhaust gases by preventing the formation of 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 replacing the filter (if installed) at regular intervals (see subsection 2.2.7 and subsection 2.4.1).