Alright guy I done what I know im a heavy equipment Mechanic I don't work on passenger vehicles much but I got this 2004 6.6 lb7 customer said that he parked it one night next day no start where what should I start.
Welcome to the DF, the most common problem with a no start is an air leak in the fuel system. The CP3 injector pump pulls a vacuum from the tank as there's no fuel pump pushing the fuel so leaks are hard to find as they suck air into the system. at the fuel filter head there's a primer that you manually push till it gets hard then open the bleeder screw and check for air bubbles, repeat if necessary till air bubbles are gone. If it fails to get hard it's sucking air somewhere in the fuel line or the filter head itself.