[Ranger]

The FPR is a small canister mounted on the fuel rail with a vacuum hose attached to the top of it. There is a diaphram in the center of it with fuel pressure on the lower half and engine vacuum on the upper half. If the diaphram ruptures, raw fuel will leak into the intake manifold and cause a rich condition affecting fuel milage and hot engine starts. If ruptured it will act much like an applied choke on a carburated engine (aiding cold starts and hindering hot starts). To check it, simply pull the vacuum hose with the engine running (or key on, engine off) and look for fuel leaking out of the nipple. There should be none.

On the '93 & '94 4.6 Northstars the FPR is inside the intake manifold and since it is subjected to manifold vacuum, there is no need for a vacuum hose. On these engines you simply turn the key on but DO NOT start the engine as it will run away unthrottled, and look for fuel leaking at the nipple.

NOTE: the pics below are for '95+ engines.