I think I've got a problem with the fuel coming to the engine.

I've got a 4bar pressure regulator on my Esc Cos so it should sit at 4.00bar without the vacuum on it on tickover. Well, it's not.
These are the values I get

3.87bar at tickover without vacuum pipe
3.20bar at tickover with vacuum pipe
3.00bar on overrun
5.50bar MAX
And especially that last part is worrying me. I'm running about 1.8-1.9bar peak boost and I doubt that the fuel pressure can be that low then.

Does anybody got any ideas???