Last night filled the old 92 up after101 miles it would only hold 3.8 gallons,this is over 25mpg normally she shows 14.8 lately.Some things done last weekend were repair a very tiny fuel leak under the rear tank strap,blocked off the return to the front tank as it is never used due to leaks and fuel pump issue.And when I dropped the front tank to see if I could repair it it was dang near full even tho I have owned this truck for 7 years and never put fuel in the front tank.
I think this thing has been returning the fuel to the front tank(recall has been performed,check valve installed) and when I blocked it now all the fuel is returning to the rear as it should.One other thing that could be affecting my calcs is we had some slightly contaminated fuel at work(47 gallons of unleaded mixed with around 7 gallons of diesel) so I volunteered and put around 7 gallons of this stuff in the old girl topped it off.But using an electric pump it filled all the way up into the filler hose wheras the station pump won't. any ideas? can this beast really get mileage like this? 300 6,3.08 gear e4od driving like an old man to work?

 

No way your truck is getting 25+ MPGs. Sounds more like the typical fuel vent problem these trucks experience from time to time. Very common for these things to trip off the fuel shutoff on real fuel pumps at the gas station.

If you did not run the vent line to the charcoal canister in the engine compartment, which is "vented" by the canister purge valve (CANP), you will probably continue to have this re-fueling problem.

 

I'm having this issue, and I'm very sure my canister isn't operative anymore, where is it located on a F-150/Bronco? and what do I need to make it functional again (let's assume the system was ripped off at some point)?.

 

Passenger side frame rail, just below the battery tray. If it is missing, I don't know whats needed to repair the system. If it needs replacing, I think NPD or LMC or somewhere have new ones that you can swap out.

 

14.8mpg is low for a 3.08 geared 4.9L truck while 25mpg is probably a bit high of what you can expect but not entirely impossible. What year is it and does it have stock sized tires on it?

 

And should I search by "charcoal canister"? doesn't sound like the proper term to me, hehehe.

 

Wouldnt say that going a mile back and forth to town for a tank got me13 mpgs

 

I believe so. That's what I have been told it is called.

 

It is a 7 mile trip one way to work, I have never had an issue with the tank filling so don't think that's an issue maybe the extra when fueled at work and clear to the top of the filler neck is the diff.will know more after next weeks fuel up.
I do know last year it averaged 15 mpg pulling racecars to the strip over hilly terrain consistently 50 miles one way,normal refill after a trip to the track was between 6 and 7 gallons. And on a 300 mile round trip to pick up a 55 ford for a friend to years ago it averaged 16 mpg hauling the car and trailer at 65mph on mostly flat terrain as we stopped and fueled every 100 miles or so and calculated mileage. PS my gauge is stuck so I'm **** about fuel range because I hate walking.

 

It's a 92 with 235/75r15 tires, as I said up to this point mileage has seemed low I chalked it up to the backroad hilly ride to work as it was weird it got better mileage when only used to tow a race car but that was 50 miles one way over mostly highway.

 

Not impossible but not likely. When I bought my truck and when my "new" engine was installed as well, I averaged just over 25 with a 302/5 speed. It idled high and I discovered a vac leak due to the PCV. The thing was pretty gutless low end and the lean mixture got it HOT, but keepinf my foot out of it I was astonished at the MPG's. Of course, now that everything's fixed and back to factory specs, my mileage dropped and I'm now getting slightly over 20 hwy.

 

I fully agree...The upmost BEST I've EVER gotten, was 22.8 with that combo...But that was with EXTREME hypermilling the truck to squeeze EVERY mpg I could.

But on a typical day...15-16 in town, 18-19 hwy and 17 mixed.

That mpg was confirmed by filling the fuel tank until the gas was at the little flapper and the re-fuel was the same. Visual confirmation on both. 60-some miles and it would NOT hold 3 full gallons. Had to call it even when the fuel ran out of the filler hole at 2.9 gallons.

 

If you have dual tanks you can sometimes get problems with the selector swiches (not the electrical switch in your dash, the actual valve), or in the case of some models like mine it's the valves in the fuelpump itself, and you can pump fuel between the tanks while running the engine.

Mine did this, and i was sometimes amased how much mpg i could get, and sometimes confused by how fast it got empty, depending on wich tank i ran on. Then i noticed that the other tank was mysteriusly empty or in some cases got full all by itself, wich resulted in it overflowing at times.

Got me confused that one, you've got to love electrics!

(edit: But yeh, the nossle probably doesn't fit well in the filler pipe, and the pump thinks it's full even though it's not, or you'd notice other problems/wierdness)

 

Charcoal or vapor canister will yield you some good hits on a search engine.

Looks like this:

 

Have you checked the accuracy of your odometer?