'86 F-250 puking fuel from fuel line near fuel pump

cadunkle · #1 (**permalink**) 10-26-2009, 08:21 PM

I have an '86 F-250 originally 351w carbureted, now 460 carbureted. Dual tanks, no emissions equipment.

Noticed I went through a lot of gas the other dayon the front tank, thought it was odd and today I smelled gas near the front of the truck. Popped the hood and found my crossmember was wet with fuel, dripping out of the fuel line near fuel pump. There are two lines, one goes to the fuel switch and then to pickup tube in each tank, this is obviously hooked to fuel pump.

The other line is presumably hooked to the other tube (vent?) in each fuel tank sender. This line I had capped, but the rubber had broken off and leaked fuel. I've never had fuel come from this line on any of my other '80-'86 emissions trucks where I capped it. I saw fuel dripping from it, and removed gas cap from each tank. Front tank sucked a LOT of air in, and as I eased it of I heard the fuel tank pop (must have had a lot of vacuum). I put cap back on and checked the leaking fuel line near fuel pump, it had drained of fuel after letting air into the tank. About 5 mins later I pulled that fuel cap off again and it let a smaller amount of air in.

I'm guessing fuel cap (vented) has failed and no longer venting air into the tank as it empties. I find it strange that this would puke fuel out the line up front though. I swapped fuel caps and I'll see if it builds any vacuum tomorrow after work.

What is that fuel line that's leaking? Should I plug these at the tank fuel sender and remove the lines altogether? If so I presume I have to plug the lines at the fuel tank switch to? Also, shouldn't the little vent on top of the tank with the check ball allow air into the tank? Check ball should only close if truck rolls.

Any thoughts?

6fifty_f1fifty · #2 (**permalink**) 10-26-2009, 08:42 PM

In my motorhome, the return fuel line I think is pressurized. The theory behind it is to prevent vaporlock, the fuel line splits near the engine, so fuel/has somewhere to go an circulate (and cool) when the engine compartment gets really hot, I.E. with a big block like that in there. This allows the fuel to be continually flowing regardless of the fuel demand, if you capped the return lines the pump could be providing enough pressure to cause a vacuum in your tank and cause your cap to leak....?

my 2 cents. not an expert or anything like that you know...

cadunkle · #3 (**permalink**) 10-26-2009, 09:12 PM

This truck is carbureted with no regulator, and shouldn't need one. I have no problems with vapor lock of heat in the fuel. It's rare for carbureted applications to even have a regulator from the factory, much less a return style regulator. I'm fairly certain this is not the system Ford used, except on fuel injected vehicles (the fuel pump is what heats the fuel with electric pumps).

6fifty_f1fifty · #4 (**permalink**) 10-26-2009, 09:26 PM

Could just be that it is in a E-350 (smaller compartment and all is why they put it in mine... It is an 88 year according to the title but the chassis was an 87, built in late 86, so it could be that rarity you are talking about. Any how, It was just a thought to your problem.... sorry can't help you more.

cadunkle · #5 (**permalink**) 10-26-2009, 10:19 PM

So your '88 E-350 is carbureted and has a return style regulator after the mechanical fuel pump? Curious as this would be odd but maybe motorhome/heavy truck related.