focus tdci won't start/run
 

i have a 2002 '02 plate focus tdci. it ran perfectly for 144k miles with no faults. one day it went to limp mode. fault codes were fuel rail pressure low and cylinder 4 above knock threshold. i got all 4 injectors and the fuel pump reconned. fitted new filter and clear supply line (to check for air ingress) and now it won't start. it will sort of tick-over for 2-3 seconds but dies. it piles out blue/white smoke while turning over. the correct fuel pressure is there and there are no fault codes showing and no warning lights. i put a new cam sensor and new glow plugs in recently. the engine has never lost power or economy and never used a drop of oil or water between services so i'm confident it's in good nick. any ideas?