As said there is an Allen screw to adjust the pressure when new there was an alloy fitment in there to stop people tampering with it, and for good reason as there isn't a need to adjust it unless you have aftermarket chip which rarely are written for different than standard fuel pressure (3.5 bar).

To have it removed is pretty common unless you are lucky enough to own a totally standard one that has not been played with and will not effect running at all.

Whats wrong?

Martin