freelander TD4 2006 - fuel rail pressure decays back to zero after ignition switch off

hi I have a 80k mile freelander td4, changed rear wheel arch pump and filter , fitted non return valve, change o ring and backing ring on fuel rail pressure regulator. had the car on a run on the diagnostics and all seems to be running fine. only thing I can see is that the high pressure side decays back from running pressure to zero very fast on switch off.
I do have problems starting from cold with some white smoke and initially takes a couple of goes to start, once started I have no problems at all.
when I try to start the engine in the morning with my diagnostics connected the diagnostics show low pressure fuel side fine, but zero pressure at high pressure side, once I turn the engine over the high pressure come up within about a second, but im wondering if this decay in pressure is causing the starting problems.
if someone has a diagnostic checks on another TD4 engine and shows the fuel rail pressure after ignition switch off and how long the high pressure holds. that would be greatly appreciated.
thanks

The high rail pressure does collapse after shutdown, that's normal.

The high rail pressure does collapse after shutdown, that's normal.

Nodge68 said:

The high rail pressure does collapse after shutdown, that's normal.

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thanks very much for your response

ive traced this problem further, tracked it down to EGR valve, the EGR valve is clean and operating on the bench, but im not getting any vacuum from the control actuator when its fitted to the car. If I take the vaccuum supply side direct to the egr, the egr valve opens as it should. can anyone tell me where the signal for the control valve comes from and what voltage I should be getting to the connector, thanks