I've just seen your posts about pollution fault codes,etc. Before looking at the HP side of your car's injection system my advice would be to check the LP components first. These comprise the LP pump in the fuel tank and the fuel filter. If either of these is restricticting fuel flow to the HP pump, the sorts of fault codes you have been getting will occur, particularly when the engine is under load (e.g. going up a long hill). First, you should replace your fuel filter element (not very expensive) if this has not been done recently. The next item to check is the supply voltage going to the LP pump from the Fuse-Relay unit, which is located in a plastic box above the O/S wheel arch in the engine compartment. If this voltage is low, or intermittent, it could give rise to the type of problem you are experiencing. The Fuse-Relay box on Eurovan2 cars often suffers from water ingress/corrosion because of leaks/drips coming from the plastic scuttle between the windscreen and the bonnet. It might be worth your while to remove and inspect it, if only to eliminate it as the cause of your problems.
Good luck!
N.B. Check the fuse relay box on the off-side wing near the washer fluid reservoir. Fuse F2 is the one supplying 12V to the fuel pump. Also, pin 11 of the (grey) connector D (PP2) is the 12V feed to the fuel pump.