1999 Jeep Grand Cherokee Sudent turns off

The car was stopped at a light and sudently shuts down
i tried to turn it on again and it will not start, just like it had no gas, i just unpluged th fuel pump relay and plug it again and it start, half and hour or so later it will turn off again, did the same procedure and worked, what could be the cause of this behavior, the fuel pump?

thanks