Exhaust Gas Recirculation: Description and Operation

The EGR system returns a small metered amount of engine exhaust gases to the intake manifold where it is mixed with incoming air and fuel. This air/fuel/exhaust mixture lowers the combustion temperature, which reduces the formation of oxides of nitrogen (NOx).

Exhaust gas recirculation is controlled by an EGR control valve. The EGR control valve is installed "in line" in a passage between the exhaust manifold and the intake manifold. Earlier models use external tubes to route exhaust gasses from the exhaust manifold, through the EGR valve, and into the intake manifold, while on later model engines, the gasses are routed through internal passages in the cylinder head. The EGR valve is controlled by a ported vacuum signal, taken from the carburetor. This vacuum signal is modified depending on the vehicle, to control the amount and timing of exhaust gas recirculation.

Fig.11 - Backpressure Activated EGR Valve:

The EGR system for 1980-82 California models consists of an EGR control valve, actuated by a ported vacuum signal, modified by a thermal vacuum valve. The thermal vacuum valve blocks the vacuum signal when engine coolant temperature is below 113'F. The EGR control valve, Fig. 11, is of the back pressure activated type. The vacuum signal operates diaphragm (N), only exhaust manifold pressure is high enough to force diaphragm (M) to close opening (I), Fig. 11, sealing the chamber.

The EGR system for 1980-82 R5 Federal models, employs a system to activate the EGR control valve as a catalyst overheating protection. Under normal conditions, the EGR control valve is actuated by a ported vacuum signal regardless of coolant temperature or transmission position. The overheat protection system operates when the choke knob is in any out position, closing the contacts on the choke control switch, transmission is in neutral, and coolant temperature exceeds 113 F.

In this case, a solenoid vacuum switch is energized, and manifold vacuum is applied, through the solenoid valve to the EGR control valve.