[boschmann]

A '91 Fox should have an AFC Digifant II system, not the older CIS-E mechanical FI system that requires special gauges. Any simple fuel pressure gauge will work. There is a small bolt plug in the end of the fuel rail, remove it & slip the gauge's hose over the fitting. Pressure should be 35-40 psi running & rise to around 45 with the vacuum hose disconnected from the fuel presure regulator (opposite end of the fuel rail). After shutting down the pressure should not drop below 29 psi after 10 minutes. That would indicate a stuck open injector or bad regulator.