hello, my 79 has dual fuel tanks. a few years abo, i had an electronic fuel pump installed becuse the mechanical one no longer worked, also my mechanic only plummed the electric pump into the front tank since the rear tank was no good any more. now my problem is that the rear tank has recently started to leak. i noticed that there was gas coming out near the gas cap so i popped that baby off and poof! about 3 or 4 gallons came shooting out. so i put the cap back on and got the gas cleaned up. after about a week, i notice that there was more gas coming out by the cap so again i popped the cap off with the same results. this time after i had popped the cap off, i left it off and about 5 minutes later, gas just started coming up and out again, but just in alittle steady trickle, i had the truck running too (starting issues).

i was wondering, are these tanks pressurized because i dont see why gas would just keep coming out, i left the cap off for about a half hour, and the trickle would start and then stop again every few minutes. also if i turn the key and flip the selector switch on the dash to rear, the gauge reads well below empty, but damn more just keeps comin! besides the chance that the tanks are pressurized, are they in any way plummed together? the truck has the california emmissions package as well. any advice would be greatly apreciated. thanks
keyul

 

I resume the weather has been hot ?

Causing Gasoline and vapour expansion

You may not have the correct gas cap on that tank either.

 

A pinched or collapsed vent hose may cause the problem. The vent hose MUST be taped to the fill hose (as Ford did originally). If the hose is not taped, it can cause fuel leaks and will also impact filling the tank...making it even slower than normal.

 

Click the links to the photos in post #8 on this thread.

https://www.ford-trucks.com/forums/6...ht=fuel+filler

 

the tank is vented to the fill tube, and its not too hot out right now, only about 65 with coulds. the first time i poped the cap off, a lot of black tar/sludge lookin stuff came out with the gas, the second time a few weeks later the sludge was not presen when the fuel came shooting out again. i noticed that when i look at the tank, there is some of that tar lookin stuff all around the edges. i think the tank is just completly garbage right now. i only left it in before because it wasnt leaking so there wasnt a need to remove it. now i think ill just pop the cap off and leave it off so whatever pressure/fuel is in there can be released and ill drop the tank after that.

 

Black tar could be Carbon Emissions mixed with the fuel ..Maybe this system is partially to blame and needs inspecting.

 

I am curious to know if you had drained the tank of gas when you made the decision that it was bad? I would siphon off the fuel that is still inside, you are hauling around an extra 150# of weight. I would also be curious to know if somehow the switch was allowing gasoline past it, filling up the bad tank, or if it was being transfered by siphoning. I would drain, and disconnect the fuel line going to the bad tank, and completely bypass it from the main system if it hasnt been already.

 

thank you for the diagram, i couldnt find that before anywhere! well the bad tank hasnt been in use for 10 or so years according to my uncle, my mechanic had just re affirmed the fact that the tank was bad so he didnt hook the electronic fuel pump to it. i myself was also wondering if the switch was bad and allowing good fuel somehow to pass into the rear tank because after the first inital blowout of black tary gas, a few weeks later when it happened again, the gas looked suprisingly good. so i threw a small pair of vise grips with with two tiny metal plates on to clamp the line closed. i left a pan under the tank over night and all the gas leaked out slowly into it so now i know for sure there is nothing left. i'll drop the tank this weekend end be rid of the dead weight.

 

How hard is it to upgrade to an electric fuel pump?

 

its easy. Do a search on google for electric fuel pump upgrade, or check in the writeups here. I would invest in a oil pressure switch that will turn the pump off when the motor is not running. If you get into a wreck, the pump will still be pumpin, not good. Its not as good as an inertia switch, but will help you not burn in flames.