EFE Valve: Description and Operation

Fig. 16 Exhaust heat control valve--HCV:

Used on some V8 engines, this system, Fig. 16, provides quick induction system warm-up for better cold engine fuel vaporization.
A vacuum operated heat control valve mounted between the exhaust manifold and pipe, directs a portion of the exhaust gases through the intake manifold during engine warm-up. On cold starts, manifold vacuum is directed to the heat control valve (HCV) through the top two ports in HCV PVS (ported vacuum switch), closing the HCV. When engine coolant temperature reaches a predetermined value, the PVS closes off vacuum and vents the PVS allowing the HCV to close under spring tension. The three PVS valves used may be identified as follows: