I have done a lot of research on the Forum and internet on the proper fuel pump pressure and am still not clear on it. My 2003 XKR has the schreader valve on the fuel rail that measures 49 PSI on the mechanical gage. My Bosch code reader says the PID fuel pressure is 55 PSI. Jaguar says it should be 5.0 Bar which equals 72.5 PSI.

As I understand it, the fuel injectors want to see the "absolute pressure" meaning the mechanical fuel rail pressure adjusted for both atmospheric and engine vacuum. My engine vacuum at idle is 15 to 22 In-Hg ( or 7.4 to 10.8 PSI).
Looking at the PID pressure of 55 I subtract 15 PSI for and atmospheric pressure at sea level and add back the vacuum from the intake manifold, about 10 PSI, and come out at 45 PSI.

Since that matches my mechanical gage it indicates the Fuel Pressure Sensor is "'OK". In actuality, the car runs great but when I "get on it" it throws a P0420 code for the Bank 1cat low efficiency.

My question is: when should I see 72.5 PSI and and I in danger of melting a piston upper ring seat?

Thanks in advance for your help!

 

55 psi is what I see on my XK8. As you said, this is the pressure differential the injectors see, so the "zero" is the manifold pressure (vacuum for me, pressure or vacuum for you). That is why there is a vacuum line to the manifold on the sensor.

At this point, I would encourage you to check the fuel trims. FWIW, an app with an ELM327 allows to record the readings, allowing you to focus on the road...

 

The 70 PSI reading should be about MAX and 55 being NORMAL.

bob

 

One would assume this would be under boost. As your supercharger builds pressure (an additional 15psi?), it would have to be added to the fuel pressure to maintain the pressure differential that the injectors are working off of.