Recently have noticed my fuel tanks acting rather retarded.
I did a test yesterday, and heres what happened.
Both tanks were reading empty or close to it. Yesterday night before I left work I completely filled ONLY the rear tank. Its about a 5 minute drive from work to my house. So I flip over to the rear tank while refilling and leave it on the rear tank. The gauge read past the F mark.
This morning, I go out, start up the truck, and notice the gauge is now reading at the halfway mark... while it is still on the rear tank. I am sure I have NO gas leaks anywhere because I've checked that more then once. So I flip over to the front tank, and of course, that is now reading past the Full mark.

My fill up prior to this one (completely filled BOTH tanks), when I would run on the Front tank, it would seem it was sucking gas from both tanks because the level on both of them seemed to go down (even though I never switched between the two, only was running on the front tank).

These events have only recently just started... and I really have no clue what the hell to expect from these tanks anymore now.
Could the thing that switches between what tank it sucks from be going bad? would this allow gas flow from one tank to another as well? Also, could it be sucking gas from both tanks at once?

Thanks, not that big a problem, but still would like to know whats up with it

 

hmm...maybe it's a problem with your tank selector valve? if it's sucking from both tanks (supposedly), could it be that it's not closing all the way?
just a guess

 

I have noticed a gas smell from outside the truck towards the front tank's door. Could just be because I have the vent line plugged off so fumes are coming from the neck out the door probably.

Don't see any visual signs of leakage anyway.
Crawled under and found the thing both fuel lines run into, so I'm guessing thats the selector that could possibly be bad. Is that thing the pump as well?

 

yes, what you found is probably the selector valve...and, no, it's not a pump. that just switches between the tanks. on my truck, mine went bad...and a brand new one ran for about 60 bucks, so I just took the valve out of there, and ran the fuel line directly to the one tank. thats the only thing i can think of right now...what year is the truck? EFI or Carbed?

 

It is an 84', carbed 351w.
If I just took that switch out and ran a y-type fitting connecting the two lines into the single, would that just mean it would run off of both tanks all the time rather then having to switch em? That would'nt be so bad if it could work like that.
And I would still be able to read the level on each of them with the switch in the cab... but what would happen if one tank went empty?

 

For a carb engine, the selector valve is JUST a solenoid valve. It's not a pump or reservoir. Any parts store ought to be able to sell you a new valve.

Don't Y the fuel line - it'll pull fairly equally until the tanks get low, and then it'll pull air from the higher tank (path of least resistance). And if you have the vent lines plugged, it'll be even MORE unpredictable. The more thoroughly you repair the WHOLE gas tank system, the better the truck will run.