have you tried a code reader onto the van?have a good look at all fuel pipes and connections in engine compartment for chaffing/drawing air,filter head got a hand primer?would have a good look at that also,very hard to say but have heard of people with same problem and can be a nightmare to repair,would see if there are any codes there to maybe point you in the direction of pump/injector issues also good luck
cdc, January 2011
