Fuel pressure problem

[dubie]

As i drive the truck more and more, we keep working out the bugs that comes after a fresh build. One we found a couple days ago had to do with the fuel pressure. We filled the tank, which is the original behind the seat one, went for a cruise and parked at a buddies house. When his neighbour came out to see my truck, I opened the door and it smelled like fresh gas in the cab. SO I checked the tank and the fitting was leaking. The strange thing is, it only does it after the truck has been running and has been parked and shut off. I checked and the fitting was a bit loose so I grabbed a couple wrenches and tightened it all up. Then I took it for a ride last night, come home, park it in the shop and go into the house for 10 minutes. I come back out and it was slowly dripping past the flare and the fitting. I assume this is the fuel making it's way back to the tank from the line. Which leads me to belive that this was the reason why the truck had a tough time to fire after sitting for a couple days, all the fuel was going back to the tank.
So my question is, is there a back flow valve I can install to prevent this? Or should I look towards my tank and why it doesn't seem to vent properly? This is a new one for me.

[mr48chev]

Pressure doesn't build up in any fuel tank when the vehicle is running but you are correct in that after you shut the truck off on a hot day pressure might build in it as the heat expands the gas in the tank.

But I am thinking that the fitting or flair is the problem and not pressure in the tank.

I'd take the fitting and line off the tank and examine the flair real closely to make sure it wasn't cracked right around where it flairs out from the tube. Then check the nut to make sure it isn't compromised and check the fitting that the flair seats on. A lot of times guys loosened them up when they pulled the engine so the gas wouldn't siphon out of the tank through the fuel line and if this is the case there may be dirt or crud or corrosion on the fittings or flair.

[dubie]

I can rule out the build up of crud already because everything is new but I will check the condition of the flair. It was difficult to see if it was leaking around the threads or if it was getting past the flair and leaking out along the actual line

[1project2many]

Also, don't just tighten the fitting. Work the wrenches back and forth a couple of times. Each time you'll probably notice they feel tight at a different spot as the tube and matching fitting seat.

Is your fuel line anywhere near the exhaust? It's possible that heat from the manifold is heating the fuel after the engine is off and causing it to expand. Does the line leak if you loosen the cap after shutting down?

Ultimately that flare fitting should be able to handle hundreds of psi more pressure than what's at the tank without even thinking about it.

[Coupeguy2001]

Try using a flaring tool to make sure there are no high spots in the flare. You can use some Machinist's bluing to check for high spots. Just roll the taper in and out a little then check.