Been having trouble keeping my truck running at temperatures below 40 degrees. It will start but when letting it warm up it idles really rough then will sputter and die, usually just before that happens the check engine light will come on. I will restart after cranking it over with the gas pedal held to the floor, and do the same thing!! Last time I drove it it would run rough after starting when warm. I've already replaced the lift pump (Dec., 2012), glow plugs and injectors a couple months ago!! Thinking it's air in fuel system, and found a rust hole in one of the fuel lines under the cab, but can't tell which one is supply or return!! It also lost prime after being parked for 2 weeks. I'm stumped and need help figuring the problem out!!

 

Um, your truck doesn't have a "gas pedal"... In any event, holding the go-pedal while cranking does nothing; the PCM ignores it.

The fuel supply lines are larger diameter than the return lines. Is the leak you found before or after the tank switcher? Have you tried running it on the other tank?

 

the hole I spotted is in the top line along the frame underneath the cab in front of the tank selector, and I would try to run it off the rear tank, but that tank has a hole in it

 

top line is the return line.

have you checked the fuel pressure? that pump could have crapped out. never know.

 

That will be one of the things I will check when the weather cooperates long enough to do so!! By the way thank you for telling me which line was the return line, still new to the diesel world, and i've owned the truck for 19 months.

 

Did some diagnostics last night by pulling the supply line off the lift pump and attaching a fuel line ran into a 5 gal. can of diesel. Determined that the lift pump is getting weak after only 6,000 miles. Bad thing to find out 2 months after the warranty ran out on the pump!!! Now trying to determine which lift pump is the best on the market..