Fuel pressure diagnosis questions on a 2007 XC70

[walterschweigert]

I am trying to chase down the cause of a brief engine stumble which is sometimes followed by a stall immediately after starting. It is not consistent but usually happens after sitting for more than an hour or so. Never does it twice in a row on a restart. Runs and idles smooth otherwise. The plugs have been changed recently, with no change. NO CODES with a generic OBD-II code reader.

What should the fuel pressure be with the key on in position II but not running?

How long should the fuel rail maintain that pressure when the key is then turned off?

What should the fuel pressure be with the engine running?

Is there a procedure for diagnosing or checking the fuel pressure sensor?

How long does the pump run when the key is turned to position II, and should I be able to hear it when standing at the rear of the vehicle?

What other component of the fuel injection system should I look at other than the pump, fuel pressure sensor, injectors?
Does the system have a fuel pump relay, fuel pressure regulator/compensator? How are all these tested or diagnosed? What are their symptoms when they start to fail?

I have searched the forum but have NOT found the answers to many of these questions so HERE they are, for the benefit of everyone. Just need some answers.

Thanks in advance.

WS