1992 Oldsmobile 88 Fuel pump

I'm getting no power to the fuel pump sometimes like on day I can start it and drive somewhere turn it off and it won't start back but after it sets a while it will start today it just died while driving and would not start back I know it's not starting because of loss of fuel pressure because when it does this there is no fuel pressure on the fuel rail and I don't hear the pump running I have checked the fuse and relay under the dash on the passenger side also I have pulled the pump and checked it and it works so then I pluged it back up without it being in the tank and let someone turn on the ignition first it would come on then after turning the key on and off about five times it would stop getting power I've also done this with it in the tank and the car would start about five times in a row the would quit Starting then after about 30 min it would start again so u got me on what it could be