2000 Jaguar XJ8 Fuel regulator test

Engine Mechanical problem
2000 Jaguar XJ8 V8 Two Wheel Drive Automatic 111k miles

I get codes P171 and 174, both banks lean. Replaced fuel filter. Checking the fuel pressure at the port with engine on and off it was about 35 PSI, and would drain to zero almost as soon as engine was shut off. Then I started it again, pulled off the regulator vacuum hose and the pressure climbed 5 lbs. I then pinched the regulator return line and it climbed to 70 lbs.
Cleared the codes, started and drove, while watching fuel pressure. No drivibality probs till pressure dropped below 50 lbs. Now pulling off the vacuum line does nothing, but pinching the return line does still raise the pressure. Pressure stays up with engine off for long time.
What up, and what should the correct pressure be on this car?