What is the function of the second port on an EGR valve on a 1979 Ford F150 351M engine when EC diagram shows only one port.?

The second port on the EGR valve of a 1979 Ford F150 351M engine typically serves as a vacuum or pressure source for EGR operation, allowing exhaust gases to recirculate into the intake manifold to reduce emissions. While the EC diagram may only show one port, the additional port may be used for a different function, such as facilitating proper valve operation or accommodating various engine configurations. It is important to ensure proper connections during installation to maintain engine performance and emissions control.