Loosing prime detroit 60

If it is a glass bowl filter there is a check valve that is located on the inlet side of that filter housing. I replace them all the time because they get trash clogged in them and allow the fuel to flow back. Check that first before doing the return valve on back of head or off of the head. It is a spring loaded ball check. I can get you a part number tomorrow.

 

DVC 101132 Putting one in right now.

 

Have you take the secondary filter off after running the engine to see if it is full. You have to hook up clear hose to see if it is sucking air, if not hook up in return to see if you air. May have compression getting in the fuel system. Keep in mind that if you bypass the water separator the pump has to pull fuel all the way from the tank. It is possible for fuel to return back to the tank.
Hope you find the problem.

 

Did you ever figure this problem out?

 

I know this is old but there’s another possibility. If the truck has fuel tank isolation valves on top of transmission, being it’s a 99, it very possible that one of the valve stems are worn from vibration and allowing and air leak, allowing fuel to run back over time. Have done away with or replace quite a few valves account of this.

 

So I have a similar problem with my 12.7.
Though I changed all the check valves; The one behind the head and the one at the glass fuel filter. I change the fuel lines. Mine happens to have a hard or no start during cold weather over a period of 2 to 3 days. The fuel is not gelled as I use lots of anti-gel. I can see the fuel through the filter and there is fuel present.
I had it over to Freightliner they said they had no issue starting it after a few days. But the difference was they were in a temperature controlled garage vs keeping it outside. So it's losing prime in colder weather. I wonder if it's the fuel injector o-rings. Maybe when it's cold it's shrinking and that's causing my loss of prime? I don't know what else it could be.
Other than that when it's running I have no driveability problems. If I shut it off during the day it will start right up no matter what the temperature is. But stating that the engine is warm and so is the fuel.