Emission Control Systems: Description and Operation

Exhaust gas emissions (carbon monoxide, hydrocarbons, and oxides of nitrogen) are controlled by a combination of precise fuel metering, unique engine modifications, and the addition of special control components. Combustion chamber design, intake manifold design, and fuel and ignition system design all combine to reduce the basic level of exhaust gas emissions generated by the engine.

Additionally, exhaust gas recirculation and jet air control are used to further reduce exhaust gas emissions.

Finally, a combination of secondary air injection and the action of a catalytic converter reduce exhaust gas emissions to an acceptable level.


A closed ventilation system is used to prevent the escape of blow-by vapors to the atmosphere. The crankcase is ventilated using fresh air from the air cleaner. The fresh air is then mixed with blow-by vapors in the crankcase and the mixture is vented to the intake manifold through the PCV valve.

The PCV valve includes a metered orifice which limits the flow of the crankcase vapors into the intake manifold as determined by intake manifold vacuum. Flow capacity is adequate for normal driving conditions. However, under heavy acceleration or during high speed driving manifold vacuum may be too low for complete scavenging of the blow-by gases. Under these conditions the crankcase vapors will backup into the air cleaner via the breather hose.

A closed fuel tank ventilation system is used to prevent evaporative hydrocarbon emissions from escaping the fuel tank into the atmosphere. Fuel tank vapors are contained in a carbon canister when the engine is off and vented to the intake manifold when the engine is running.