Well thats just the thing. It normally should purge on its own just from cranking.

Best you can do is fill the fuel filter up and take it from there. If it starts, runs and stalls, fill it again and restart again. Normally it shouldn't take much to clear the lines even if they are all dry. 2 fills of the filter should get it going, but this isn't a normal situation.

You said your tank is reading 1/2, what about the other one? Is that also above the 1/2 mark? The fuel selector valve can sometimes fail in one position causing it to draw from the wrong tank but your gauge will read from the correct one.

Since this is a 1986 truck, its possible your water separator is causing this problem either by leaking air into the fuel system, or in a really extreme case, could be clogged with crap. Temporarily bypassing this would help narrow down the problem. Running long term without a water separator is not recommended, but for testing its acceptable.

 

Maybe I am leaving out some details to narrow this down...the truck will start, idle, and run just fine until it gets up to 35-45 mph. Then if you are trying to keep at that speed...eventually it starts to lag a little bit to begin...feeling like it is losing power...then gaining it right back...until it will finally die IF you don't go back to around 35 mph within the first couple times it starts to lose power. I am going to go check my fuel filter right now to go see if it is filled with fuel or not but I hope this will help someone narrow the problem down. I haven't replaced the lift pump yet but I am planning on doing it tomorrow. Please let me know...and as always...thanks in advance.

 

That could be a blocked fuel tank vent. Something you can try is to pull over when it starts to stumble and pop the filler cap of the fuel tank to see if there is any suction noise, or apperant vacuum inside the fuel tank.

Its unlikely (but not impossible) for both tanks to have a blocked tank vent at the same time though so thats a bit of a long shot.

Definately sounds like there is some sort of fuel flow restriction in there somewhere. Bad lift pump is not an unreasonable possibility. Were you ever able to perform the flow test on the pump?

 

I'm not sure of the flow test that you are talking about. But other than running the truck until it starts the problem...I haven't tried anything.

 

Well...the case is solved. I went for another ride like you said to see if there was a vacuum in the fuel tank. It died on me again...checked the tanks...nothing...no sound at all. I went back home and decided to check again all the line of everything that I had replaced and all the lines for the fuel tanks. I found when I came up to the tank selector valve that when I used a zip tie to fasten the wires to the frame...I also got the supply line to the engine pinched in that bundle. I cut the zip tie...fastened JUST the wires...went for another drive and drove the **** out of it to try and get it to die again...but she wouldn't...runs like a champ now. I appreciate everything that everyone has told me about...even though it wasn't the problem this time...I now know some troubleshooting tips for when I have problems again (hopefully never). So thanks again.

 

Nice when its something simple like that. Thanks for letting us know what it was.