What causes a long crank on a 2006 e450 6.0l diesel?

Engine oil HIGH pressure from HPOP pump is TOO LOW. Sometimes just an oil change to 15-40 rotella can alleviate problem BUT usuallly the oil plugs push out of the high pressure pump and cause low oil pressure to the injectors or the ICP sensor failed. the injectors must have high pressure oil to open and allow fuel to flow. the 6.0 hpop is in engine valley just under oil filter housing..do not attempt to replace if your not a ford diesel tech..can be very expensive lesson if you're not familiar with this engine.. normal cost for this oil pump repair is about 3,000.00.