trafic starting problem

i have a 2003 19dci trafic thats difficult to start only way it starts is by priming the fuel line pump as you turn it over once its running idles good revs r good drives good soon as you turn off refuses to start up its as if no fuel so far ive changed fuel lines pump in tank full service had injectors checked and checked connections pressure valve presure regulator cam sensor crank sensor all seem ok anyone any ideas