Hey Hey! 

I have a 05 CTD that will not hold prime in the fuel filter housing. To date I have done: New FCA, Fuel pressure regulator,  relief valve, New transfer pump and module in the tank. Checked the supply and return line to the filter housing from, the tank, no leaks. tightened all injector fuel tubes. double checked all injector lines, no problems or defects. Checked my fuel supply to the CP3 660 Mil. in 10 seconds. Hot engine CP3 return to the tank 700 Mil in 60 seconds. Checked injectors return hot engine to tank 100 Mils in 60 seconds. Replaced all banjo washers with Tork Teks. Replaced the rubber hoses to and from the CP from filter housing. Also carefully inspected the filter housing cap and o ring for damage, no problems. Checked the crankshaft position sensor and the fan clutch. All Good. Any CTD fans seen this before? Cummins all the way!

Yes. 

Try parking nose down to see if the prime holds?

 

Do you have a fuel pressure gauge on the low pressure side? What does the gauge do during cranking?

Yes I tried that. No difference.  And no gauge on the low pressure side. Most of the banjo washers were in bad shape. I found 2 more needing to be replaced.  There on order. Will install and see. .could the injector relief valve be hung?

http://cppdiesel.com/cummins-3164325-rail-test-plug-03-07-5-9l/?gclid=Cj0KCQjwuYTYBRDsARIsAJnrUXC0-lWR5KP1L5-4-3OEGhJM_xMOfxXsbhISL6oArwJ8iHLoirhPGSoaAvRJEALw_wcB

 

Try these. Remove 1 injector line at a time and  install plug on the rail. My bet is you have a leaky injector. When truck starts easily you found your leaking injector. Sometimes there is more then 1 leaking  injector causing low rail pressure and loss of prime issues. I have started these engines with only 2 injectors getting any fuel feed.