Ford Crown Victoria Forum : “where is the PCV valve on 1991 Ford Crown Victoria 5.0”

If you click on figure 1 on the following page it will show you the location of the PCV Valve.

http://www.autozone.com/az/cds/en_us/0900823d/80/19/30/56/0900823d80193056/repairInfoPages.htm

it should be under the upper intake plenum, on the passenger side of vehicle. it plugs into the rear of the passenger side valve cover and has a vacume hose going from the top of the PCV valve to the rear of the intake plenum.

It's behind the upper intake manifold.  You may have to lean on top of the engine, so lay a towel or something down.  It's right behind the middle of the plenum.  It has a weird bent hose on it.  Just pull it out with your hands if able or with a pair of pliers.  If I were you I'd change the PCV screen as well.