If you have a scan tool that can display OBD system data, look for a fuel pressure PID. Compare the fuel pressure reading against specifications to see if it is in range or not. You can also compare the scan tool pressure reading against the actual reading on the vehicle with a gauge to see if they are the same. If the gauge reads higher, the vehicle may have a bad fuel pressure sensor. A low fuel pressure reading would confirm a weak fuel pump, low voltage to the fuel pump or a leaky fuel pressure regulator that does not allow the system to develop and hold normal fuel pressure.