Mustang will not start!

I can’t tell if that sounds right from the video, sorry. A pressure test would give better data. Unhook the line at the high pressure pump, plug in a gauge and test it rather than guess at it. Would confirm its ability to create pressure.

How much psi is normal pressure

70 to 80 psi. Seems your car has a fuel pressure sensor. The data should be availble on whatever code scanner you have. Seems those sensors have been a problem on earlier Ecoboost Mustangs.

The high pressure fuel system can operate at over 2000 PSI, don’t mess with it.

Start with measuring the low pressure supply, the low pressure pump specifications are 50.8 to 75.4 PSI.