Fuel pump runs continuously- 92 Jeep Cherokee

Anyone know what would cause my fuel pump to run what seems like, from the sound, continuously wide open? When I start the jeep I can normally hear it for a second or 2 while it comes up to pressure then it runs quietly. When it is acting up I hear the loud noise continuously. The last time it quit working completely. I have replaced my fuel pump 3 times and each one has done the same thing. I have also replaced the fuel filter and relay. I have not replaced the pressure regulator. Could this be causing the problem? I have a 92 Jeep Cherokee L6 4.0L

Thanks Rick