Exhaust Gas RECIRCULATION: Description

Purpose of Exhaust Gas Recirculation (EGR) System is to limit formation of oxides of nitrogen by diluting intake charge with a metered amount of exhaust gas, thereby reducing the peak temperatures of gases in engine combustion chambers. Exhaust gas introduced is inert, and much cooler than combustion temperature. Since it will not burn, peak combustion temperature is lowered. The EGR system consists of a diaphragm actuated flow control valve (EGR valve), Coolant Temperature Override Switch (CTO) and connecting hoses. In addition vehicles built before March 15, 1973 are equipped with a Low Temperature Vacuum Signal Modulator (Exc. V8 with Man. Trans.) and a High Temperature Vacuum Signal Modulator. California vehicles equipped with 360" engines with automatic transmission (Exc. Heavy-Duty Trucks), are equipped with an Exhaust Back Pressure Sensor.