Emission Control Systems: Description and Operation

PURPOSE AND OPERATION
The multiport fuel injection system provides accurately metered quantities of fuel to the combustion chambers to ensure the most efficient air to fuel ratio under all conditions of operation. A further improvement to combustion is made by measuring the oxygen content of the exhaust gases to enable the quantity of fuel injected to be varied, according to conditions, to correct any unsatisfactory composition of the exhaust.

The main components of the exhaust emission system are two Catalytic converters which are an integral part of the front exhaust pipe assembly. The catalytic converters are included in the system to reduce the emissions to atmosphere, of carbon monoxide, oxides of nitrogen, and hydrocarbons. The active constituents of the converters are platinum and rhodium. The correct functioning of the converters is dependent upon close control of the oxygen concentration in the exhaust gas entering the catalyst. The oxygen content of the exhaust gas is signalled to the electronic control unit (ECU) by oxygen sensors (Lambda sensors) located in the exhaust front pipes between the manifold and converter. The ECU can then make an appropriate adjustment to the fuel supply to correct the composition of the exhaust.


The charcoal canister absorbs and stores the fuel vapor that is emitted from the fuel tank when the engine is not running. The vapor is purged from the canister by outside air drawn through an orifice at the bottom of the canister by the application of manifold vacuum to the top.


A solenoid operated valve controls purging of the canister. The valve is controlled by the fuel injection ECU to ensure that purge normally takes place at engine speeds above idle and when the vehicle is in motion. The rate of purge will depend on engine speed, road speed and throttle position.