Emission Control Systems: Description and Operation

EXHAUST EMISSION SYSTEM [VEHICLES WITH CATALYTIC CONVERTER]
Exhaust emissions (CO, HC, NOx) are controlled by a combination of engine modifications and the addition of special control components.
Modifications to the combustion chamber, intake manifold, camshaft and ignition system form the basic control system. Additional control devices include an exhaust gas recirculation (EGR) system and a catalytic converter.
These systems have been integrated into a highly effective system which controls exhaust emissions while maintaining good driveability and fuel economy.

AIR/FUEL MIXTURE RATIO CONTROL SYSTEM [MULTI PORT FUEL INJECTION (MFI) SYSTEM]
The MFI system employs the signals from the heated oxygen sensor to activate and control the injector installed in the manifold for each cylinder, precisely regulating the air/fuel mixture ratio and reducing emissions.
This allows the engine to produce exhaust gases of the proper composition to permit the use of a three-way catalyst. The three-way catalyst is designed to convert the three pollutants (1) hydrocarbons (HC), (2) carbon monoxide (CO), and (3) oxides of nitrogen (NOx)into harmless substances. The two operating modes in the MFI system are as follows:
1. Open Loop-air/fuel ratio is controlled by information programmed into the ECM during the manufacturing process.
2. Closed Loop-air/fuel ratio is varied by the ECM based on information supplied by the heated oxygen sensor.