Exhaust Gas RECIRCULATION: Operation

The EGR system operates only when the engine is warm and either accelerating or cruising. The vacuum control signal comes from a carburetor port that produces no vacuum at idle, and a thermosensor which eliminates EGR when engine coolant is below normal operating temperature. When vehicle is decelerating, manifold vacuum rises and turns on EGR control switch. The EGR control solenoid valve closes and cuts off EGR flow. Vacuum is provided to EGR control switch only above 15 MPH, when the speed sensor opens the throttle opener solenoid valve.

EGR control valves A and B use a ported vacuum signal to control a manifold vacuum flow large enough to operate the EGR valve. With this system, the EGR valve is operated by a signal proportional to airflow through carburetor venturi, ensuring correct EGR flow.