Engine hard to start up when the engine is warm

[king_julien]

Hi again, I have a 2001 4.4i Auto X5. The car starts up 1st time when the engine is cold. But once I drive the car for a hour or so and come back to the car after 10 minutes, it will crank for awhile before starting. In some cases it take a couple of attempts before starting. But when I leave the car for more than an hour and everything cools down, it starts up fine.

I am very confused can somebody throw some light as to what could be the culprit... anybody else has similar problem??? I replaced plugs, sprayed WD40 on every connectors but nothing seemed to solve my problem. And also I realized when I open my fuel cap, there isn't any pressure. Could this be to do with fuel pressure regulator.