02 trafic wont start?

was driving my trafic then massive ball of black smoke out the back and die , got it home it would start run for 5 secs sound like marbles in the pump and cut out. took it to a local garage where they replaced the pump ,injectors and tried all the sensors off another van no luck we had it turning over for 2 days trying to get to the bottom of it and out of no where it started for 5 secs the marbles came back and nothing again can anyone help as im at the end