High pressure pump sounds like it could be on its way out to me. Requires alot of pressure to start a diesel. You could have a faulty non return valve if theres one in the system on that van or a weak lift pump in the tank. Injector leaking/returning too much diesel. Theres loads of possible things that can cause non starting on a diesel mate abit hard to help without actually looking at it. Hope you get to the bottom of it though.