ignition problem in Nisan Tsuru 8 valves

Hello

friends, I need your help. I have a 1995 Nissan Tsuru 8-valve red valve cover. I've had to replace the fuel pump four times in the last year.
This last time, I took it to the mechanic because it wouldn't start. He diagnosed it as the fuel pump again, so I bought a new one, and the car ran for a few hours, then suddenly it wouldn't start anymore. I took it back, and he diagnosed the fuel pressure regulator as damaged. I couldn't find a replacement anywhere, so I bought another regulator from Nissan. The mechanic adapted it, and the car ran perfectly for a few hours. I parked it at home, and after a while, I tried to start it, but nothing. I already checked the fuel pump pressure, and it reads around 20 psi. I don't know what to do anymore. I would appreciate any suggestions you might have!