FREIGHTLINER WITH NO START ISSUE

I HAVE A 2012 FREIGHTLINER CASCADIA WITH A DD15 IN THE SHOP THAT WE HAD THE OIL FILTER GASKET REPLACED. WE ALSO DECIDED TO DO ALL THE FILTERS AND AND AN OIL CHANGE. WE THEN REPRIMED THE SYSTEM AND WENT TO FIRE THE TRUCK UP AND IT RAN FOR ABOUT A MINUTE AND A HALF THEN DIED. WE REPRIMED THE SYSTEM AGAIN A COUPLE MORE TIME BUT IT WOULD NEVER FIRE UP. WE PULLED THE FILTER AND FOUND A RETAINING CLIP THAT HELD A CHECK BALL IN PLACE HAD BROKEN OUT. WE REPLACED THE FUEL FILTER HOUSING AS THE 3 FILTER HOUSING IS HARD TO COME BY TO THE TWO FILTER CONVERSION AND WE STILL HAVE THE SAME ISSUE. WE FOUND THAT THE LOW PRESSURE SIDE HAD NO LOW PRESSURE WHEN WE CHECKED ON THE COMPUTER AND FOUND THE PIN OUT ON THE ECM WASNT GIVING US THE CORRECT READING WHEN WE OHMED IT OUT SO WE REPLACED IT. STILL NO LOW PRESSURE ON THE COMPUTER BUT WHEN WE HOOK UP A MANUAL GUAGE WE HAVE PLENTY OF PRESSURE. WE HAVE REPLACED EVERYTHING ON THIS TRUCKS FUEL SYSTEM (HIGH PRESSURE PUMP AND LOW PRESSURE, ENGINE HARNESS, INJECTORS, HIGH PRESURE FUEL LINES, ECM).

OIL PRESSURE READS AROUND 60 PSI
FUEL PRESSURE ON THE HIGH SIDE READS 275-305 Bar
FUEL PRESSURE ON THE LOW SIDE READ 0 PSI ON THE COMPUTER BUT WITH A MANUAL GUAGE IT READS 65-70 PSI

ANY HELP WOULD BE APPRECIATED