Engine light was on, had it checked and replaced the fuel sensor light back on

What is your question?

The engine light went on, the diagnostic computer code wad P0191 FORD - Fuel Rail Pressure Sensor Circuit Range/Performance. So we replaced the sensor and next day the light goes on and same code pops up. Now what do I do? The car runs real rough around 600-700 rpms and shuts down around 400 rpms