My car starts but then shuts off immediately

I was driving home one night and my car just died randomly I drove it to the side of the road but the car wasn't accelerating. The oil light came on but the oil level was fine. The car would start the cut off. I had it towed home and replaced the fuel filter and part of the fuel pump. The car still just starts and cuts right off. Im not sure what to do next. My mechanic thinks I need to replace the entire fuel pump but I can hear the fuel pump when I try to start the car. The car also died in my front yard so the check engine light wont come back on so I can check the codes. What should my next step be?