EGR System: Operation: Notes

EGR system controls vacuum under varying conditions to EGR valve. The EGR valve is a vacuum-actuated, poppet-type valve, used to modulate exhaust gas flow from manifold crossover into incoming air/fuel mixture.

A vacuum tap at throat of carburetor venturi provides control vacuum. Because of the low level of vacuum, it is necessary to use a vacuum amplifier to increase vacuum to the required level for EGR valve operation.

Elimination of recycle at wide open throttle is accomplished by a dump diaphragm, which compares venturi and manifold vacuum to determine when wide open throttle is reached.

At wide open throttle, the internal reservoir is "dumped", limiting output to EGR valve opening point. Opening point is set above manifold vacuum available at wide open throttle, allowing closure of EGR valve at wide open throttle.