This is a farm truck used to haul grain at harvest. We have been battling a loss of prime on the fuel system over the past 2 years. I installed some clear hose in place of the original fuel line on the supply side and seen that over time it was siphoning back. I finally found where the previous owner must have had a fire under the hood and it melted the parker hanifan plastic fuel hose and if i twisted the hose by hand i could actually hear air escaping. I replaced the damaged fuel line with new and installed a factory cummins check valve in the cooling plate as it did not have one. I then started and ran the truck up and down the road for a while. I parked the truck in the shed and waited 12 days and tried starting it and it started right up. That was 1 month ago and today i went to start it and it would not start without a small shot of starting fluid. I am at a loss now as i had thought i found my problem with the damaged fuel supply and return hoses. I have checked all the other fuel hoses and connections and the fluid levels were all up and i had 12 volts at shutoff wire. I have been running a napa fuel filter 3406 with a standpipe in it that is supposed to help with hard starts. Any other suggestions would be greatly appreciated. Thank you.
How about this. Block off the return at the tank inlet. Remove the fuel feed line and pressurize it with a low pressure electric pump overnight. The whole fuel system will sit with 5-10 psi on it. Maybe then the leak will show itself. Sometimes they only work in one direction but seeing as how you seem to have tried everything else it may be worth it.
Check the fuel check valve fitting in the ecm plate, it is probably stuck open, letting fuel drain back.
After running this truck more before harvest it was acting up more often. I eventually had to have the ecm rebuilt. It worked good through harvest . Thanks for the replies.