I have a 88' F-150, 4.9L I6. Does the EVP and PFE perform the same functions? Meaning would there even be a PFE or DPFE in this vehicle? I beleive its equiped with an EVP system. I'm trying to diagnose some EGR issues.

My truck runs good when I disconnect and plug the vaccum line from the EGR valve but runs rough when accelerating and the vaccum connected.

 

i beleive those had a little cube lookin evp with one vacumm hose running into the bottom of it.