Hello, I'm new here. My name is Kirk and I recently moved to MI from Fairbanks, Alaska. I've had my truck for over 12 years now and it's been great. Ran great even in the cold Fairbanks winters. I've had two major ordeals since I've owned this truck. First, the KDP got me fairly early on but since I do my own work, it was more labor intensive than expensive. The next thing to go was my P7100 believe it or not. Replaced it with a new rebuilt one...guy at the rebuild shop found that my problem was with some scoring inside. Anyway, that was all years ago and the truck has been running great.
Now to the topic of this thread. On my most recent road trip from AK, I noticed my fuel pressure a touch low and fluctuating a bit. It would idle about 20psi...after about 10 seconds, it would dip to about 10psi for a couple seconds then return to 20psi...it would continue this way while running. It was also loosing prime after sitting for several hours or over night so I'd have to prime the lift pump. First start in the morning it would run rough for a bit and then smooth right out for the rest of the day. In researching this site, I came to the conclusion that it was my over-flow valve which I just replaced with a new one. The pressures now are where they should be 22psi at idle and about 30 reved with no load. Took it for a short test drive and all was good. I then parked it for a few hours and it didn't want to start so I had to prime it. Started rough, smoothed out and the fuel pressure was still great. The overflow valve needed to be replaced but it didn't solve my loosing prime problem. I have changed the fuel filter recently, and a number of years ago, I changed the two rubber fuel lines. Currently, I see no leaks...other than normal 200k mile Cummins oil spots. I haven't done anything with the lift pump other than manually pump the hell out of it...and I haven't done anything with the fuel pre-heater or screen. I'm running out of things to look at. Is there a check valve in the lift pump? The lift pump is making great pressure so, unless there's a check valve in it, that shouldn't be the problem.
Any thoughts or ideas will be appreciated. The truck is bone stock. Thanks guys and gals.

 

you have a leak some where. you might try to put some air pressure to the tank and look for wet fuel spots. i have saw rusted lines right at the tank leaking slightly

 

Drove the truck to work for the first time today since changing my overflow valve. It started cold this morning without priming but it took a little bit of cranking. After sitting at work for 8 hours, it fired right up but ran rough for 5 seconds or so...then smoothed out.
I've been in the fuel system (filter and overflow) so I've let air in. I'm not sure how long air can linger in the system but things seem to be improving. My work is about a 15 minute drive.