msisk14

I have a 1991 LX convertable with a 5.0. I have no injector pulse. I was told it was the fuel pump by a mechanic so I installed a new one and i still have the same problem. Now I am being told it is the computer. The weird thing is if I let the car sit overnight I can start it the next morning but as soon as I turn the car off I cannot get the car started again. I checked my fuel relay and it is fine and if I spray ether in the intake it will start but not stay running. Does anyone know what the problem is?