Since owning the truck, it has been hard to start. After replacing the return line coming off the IP with a clear one, I found that I had air in there. Using the instructions here to pressurize the system, I have searched the entire length of the truck multiple times without finding the leak. Since I could not find it, I have slowly been replacing portions of the fuel supply system (don't worry this hasn't cost me more than 35$... yet :eek: ) So far I have:
-Replaced all the rubber supply fuel lines and tightened them down.
-Replaced the Fuel filter with a later model one. Before installing it, I filled it up with seafoam and pressurized it.. it didn't leak.
-Replaced the mechanical fuel pump with another one (I actually had to do this to pass inspection.. I just replaced it with a cheap one Advance Auto parts sold)
-Installed a check valve before the mechanical lift pump.

Today I still have to crank the engine for 4-6 seconds while holding my foot on the accelerator to get it started if it has sat overnight or more.
Looking at the return line before I start, I see a few small air bubbles who's quantity grows as I let it sit longer. This line has a bit of pressure in it too so I'm confused as to where the air is coming from.

So.. thoughts? Could this be something wrong with the IP? And what's with that pressure in the return line?