MERCEDES-BENZ Exhaust Gas RECIRCULATION: Description
In order to reduce nitrogen oxide emissions, exhaust gas is recirculated into intake manifold. Components of system are as follows: A vacuum operated exhaust gas recirculation valve (EGR valve), an engine RPM switch and an oil temperature sensing switch. 220 models have a single relay box, while 280 and 280C models have two relay boxes, one with an 8 prong connector and the other with a 12 prong connector. These relay boxes are also connected to other systems. In addition, 280 and 280C models also incorporate both a high and low coolant temperature sensing switch, a vacuum check valve, a vacuum reserve tank and a vacuum sensing switch. Vacuum source on 220 models is a special port in carburetor. On 280 and 280C models, vacuum source is intake manifold. These various control units ensure that exhaust gas recirculation only occurs in certain engine operation modes so that engine operation will not be adversely affected.