Alright, first the basics. 1986 F-150 Lariot, 302 fuel injected, dual tanks, (rear tank not in use) AOD. Anyways....I've been working on this....truck..for the past few months. Had to replace the hi-pressure fuel pump and while doing so dropped the forward fuel tank to check for problems. Ditched the selector valve just to eliminate any problems. Installed a fuel filter in its place. Today decided to pull the fuel pressure regulator as it's the original and I'm determined not to ruin another fuel pump due to possible high pressure problems. (I'm on the second one in 20 miles) After pulling the fuel pressure regulator I wanted to be sure the fuel return line was clear and functioning so put an air line in the port and slowly put air thru the return line. Made a funny squealing noise...didn't register in my head. Upon removing the air line I noticed back pressure from the return line port and wondered..."Why is it building pressure...possible clogged return line????" Pulled the return line off down at hte frame rail and no more back pressure....so the "problem" (if there is one is between the selector valve area (remember..selector vale is gone) and the fuel tank. Hmmm??? More to come. Audie..the Oldfart...

 

Now common sense would dictate that pressure in the fuel tank would vent thru the filler. There are actually half-moon notches cut into the filler neck (where you put the fuel pump nozzle to fill the tank) to allow the tank to vent pressure. Or so one would presume. I can't actuall get any fuel in this tank as of yet. Still working on that. But I apparently had about 1/2 gallon in the filler hose/neck from my many efforts. There's also a vent on top of the tank that vents to the charcoal canister in the engine bay. Anyways, walked up to the house grabbed a cupp'a coffe and lit up a smoke and walked back down to the truck to figger this out. Took me about 20 minutes I rekkin'. And remember..the fuel pressure regulator is laying in the garage...so the tank can (I assume) vent thru there as well. Not hearing any wierd noises/hissing or metal expanding....I twisted off the gas cap. While standing in front of it. With a ciggerette in hand. GOOOOOSHHHH!!!! I have no idea where the gas cap landed....haven't found it yet. Got covered from chin to knees in gasoline and soiled a new pair of shorts. Didn't catch fire though!! Now I've got some questions. More to come....Audie...

 

just checking the obvious...but you weren't pressurizing the tank by any chance??

Edit: Never mine....wrote that as you were writing your last response...guess that answers that question.

 

Well it's obvious the tank isn't venting...unless you count the pressure that exits when you unscrew the cap. Is there a valve on the return line inside the tank that prevents fuel/pressure from exiting thru the fuel pressure regulator port? Remember..the fuel pressure regulator is off....laying in the garage. Why wouldn't it vent thru the filler neck openings rather than the filler hole? Could I have damaged anything in the tank by putting air pressure (about 60lbs.) thru the return fuel line? Well, I can only work on this a coupl'a hours at a time so probably won't get back on it till mid-week. I'll replace the fuel pressure regulator and hook up a pressure guage on start-up to make sure the fuel pressure is correct hopefully by the weekend. If...I can get fuel in the tank....still working on that. Thanks to all. Audie....the Oldfart..

 

If the tank isn't working proper, you would be building a vacuum in the tank. After a bit,the pump will not be able to overcome that, so it is possible that is actually the source of your problems.

BTW, consider yourself lucky that the tank didn't light, it doesn't take much, and it is not a fun experience. I had one light while I was draining it from a simple electric spark. I was holding it upright when it lit, spraying gasoline out of the sender hole onto my legs, continuing to burn. The fireball made it past my head. You can likely imagine how well that went.