VENTURI Vacuum Control System - 5.2L
The venturi vacuum control system utilizes a vacuum tap at the throat of the carburetor venturi to provide a vacuum control signal. Because of the low amplitude of this signal, it is necessary to use a vacuum amplifier to increase vacuum to the level that will operate the EGR valve. 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 achieved. At wide open throttle, the internal reservoir is dumped, limiting output to the EGR valve to manifold vacuum. The valve opening point is set above the manifold vacuum available at wide open throttle, permitting the valve to be closed at wide open throttle. This system is dependent primarily on engine intake airflow as indicated by the venturi signal, and is also affected by intake vacuum and exhaust pressure.