Ported EGR System
Ported type EGR valve is operated from carburetor vacuum port. It is fully closed with vacuum less than 2 in. Hg. EGR starts to open above 2 in. Hg and is fully open with more than 8.5 in. Hg of vacuum applied. At idle and wide open throttle, ported vacuum is low and the valve is closed. At part throttle, ported vacuum is high and the valve is open for exhaust gas recirculation. See Fig 1.