I have 2006 6.0 super duty. My truck sat for a few months due to a braking system issue. However I fixed that issue and fired the truck right up. I walked away and came back and my truck was dead. I have a airdog fuel system and learned that it wasn't pumping and needed primed. Once I got it primed it still will not start. The truck sounds like it's about to however will not completely fire. This also happen in the early fall where the pump needed primed however the truck fired right up and ran fine until now. I have taken the upper filter cap off and the bowl was empty, however when I flip the key the bowl fills up quickly but then begins to bubble. The upper filter looks like it may need replaced and it's also getting to be time for the lower to be replaced. Any suggestions on what it could be or to try?