You more then likely have a small hole in your fuel line, and are sucking in air. A lot of times the hole is so small that it doesn't leak fuel, just seeps a little. Then when it is running the pressure in the lines can actually create a vacuum pulling in the air. I know this sounds funny but this is how it works. Your in-tank pump usually puts out 6psi to 10psi pressure. Then the injection pump "booster pump" pushes that pressure up to 35psi to 70psi. Since this pump is at the end of the line it is actually "drawing" (pulling) in the fuel. Think of a straw in a glass of soda. If there is a small hole in the middle you will suck in air. Same principle here. If your truck is an older model then I would recommend replacing ALL the fuel lines (hoses) . Copper has a tendancy to "work" harden then break or crack due to stress. This is one of the very first mods I did on my own truck. You can go with DOT nylon hose. It is very affordable and very easy to work with. Plus it will out-last you and your children ! I would NOT go with regular rubber style fuel hose. Most people do not realize rubber has a limited work life of so many years. Then it starts to break down.
