Exhaust Emission Systems - BMW: Description
Exhaust emission control is accomplished by a specially designed engine, intake manifold and carburetor. Four cylinder models also use a preheated intake manifold. A throttle closure delay diaphragm system is used to control emissions during deceleration. This system consists of a throttle control vacuum diaphragm, a two way magnetic valve connected to intake manifold vacuum, and a speed sensitive relay which controls magnetic valve. On four cylinder models, an ignition retard unit is connected directly to intake manifold vacuum. On six cylinder models, vacuum retard is controlled by same two way valve and speed relay as used for throttle control system. All models also use exhaust gas recirculation for the control of NOx. For additional information on EGR system, see appropriate story in EMISSION Section .