Bear, with the engine off and the key in the RUN position, you should be getting between 40-50 psi of pressure. With the engine running, you should be getting 30-40 psi of pressure. Ideally the pressure should be more up towards the higher end of the pressure band. Having a low pressure indicates either a severely clogged fuel filter or your fuel pump is starting to go. If it is at 0 psi, then you have an electrical issue with your fuel pump/fuel pump has failed.

Hope this helps you solve your issue.

 

I have a 2012 XF, regular 5.0. I just replaced the fuel pump because the check engine light is on. I had it read and it was reading high pressure at the low pressure fuel pump. So I replaced the in tank pump. Now I had it read again. It is still reading low pressure fuel system pressure is too high. So it said replace the rail pressure sensor. So I looked it up. The illustration is both a high pressure sensor and a low pressure sensor but every website I look at only specify high pressure sensors and others don't specify one or the other. Are the interchangeable and if not can someone point me in the right direction to get a low pressure fuel sensor. Thank you.

 

Try posting in the correct forum. This is X Type (X400) forum.