6-Cylinder & V8
Vacuum is tapped at the throat of the carburetor venturi or air flow sensor (EFI models) to provide control vacuum to the vacuum amplifier. This low amplitude vacuum signal is increased in the amplifier to a level which will operate the EGR valve.
A dump diaphragm compares venturi and manifold vacuum to prevent EGR operation at wide open throttle. EGR operation is determined primarily by the venturi signal, but is also effected by intake manifold vacuum and exhaust gas pressure.