2001 ivec 75e17 in limp mode showing blink codes 8.2 & 8.4?

My 2001 iveco Tector went into limp mode the other day showing fault codes 8.2 & 8.4 , i have replace the filters and priming pump no change , i then discovered it was allowing fuel back through the rail relief valve so i replaced that still no change , could it be the fuel pressure sensor or the fuel regulator which you can hear running when you turn on the ignition ?