Hijet 1.2 Diesel cuts out


Hello, can anyone help please, i just purchased a
hijet 1.2 Diesel 1998, it starts fine and runs well except over 30MPH and it cuts out, it has a new fuel pump, apparently the previous owner was told by AA man that the camshaft is probably worn and not driving the pump enough...? I have removed the camshaft cover but cannot see any wear..? the van has only done 37K any suggestions please.