Fuel Gage work fine from full to about a half tank, it than starts dropping really fast. The estimated miles to empty also starts dropping fast. I usually gas up when I get to a half tank, but the last time I ran it down close to empty. When I inserted the fuel nozzle into the fuel fill a rush of pressure vented. I never remember that happening before. FYI, My truck doesn’t have a gas cap. I was thinking the sending unit in the tank was the problem. Now I’m wondering why there is a pressure build-up and is it having an effect on the float. Is there a vent or an emission control line clogged? Is the tank supposed to be under pressure?
Thanks!

 

Do you have check engine light or have you scanned for any codes.

 

i dont see how any pressure would effect the float level reading.. the FLOAT ARM slides up and down a wire coil.. That is a variable resistor.. If there is some corrosion / dirt on the resistor and the SLIDE Goes over it, it will give a false reading... dont see any way to change the FLOAT READING other than messing up the variable resistor..

 

Im not sure but it sounds like maybe the tank is collapsing from vacuum in the tank from a defective vapor management valve or canister purge valve?

 

I thought the same, might be a venting problem. Begs the question for the OP- how full do you fill it? Canister damage has occurred more than once from folks trying to stuff every last ounce of fuel in instead of just stopping when the handle clicks off.

 

Do you guys really think the fuel pump has enough “umph” to suck in/collapse the tank, and if so, then wouldn’t the fuel level stay at a “fuller” than actual reading.

also, wouldn’t the flipper in the fuel inlet open to let air in before the tank collapsed, it’s pretty thick rigid plastic.

 

Read this thread

https://www.f150forum.com/f2/fuel-ta...lapsed-219036/

 

be easy enough to stick a straw thru the fill valve and hold it off the seat ... then drive around and test.... Might get a CODE that the valve is leaking and can not maintain tank pressure .... but would be a good test for fuel level problems.

 

The OP specifically said, "When I inserted the fuel nozzle into the fuel fill a rush of pressure vented" which made me think of a venting problem. I'm not sure how that got turned around to creating a vacuum and collapsing the tank.

 

A rush of pressure and a surge of air into a vacuum collapsed tank can be easily confused for the same thing. Thats how. Did you even read the thread I asked him to read?

 

A comment on that thread:
“A faulty Purge valve in the fuel tanks evaporative emmissions control system (EVAP) is the culprit. Instead of gas vapors entering the charcoal filter, the purge valve remains open and actual gas gets into the charcoal filter causing a huge vacuum pressure to build up and deform or shrink the gas tank. It happened on my Ford F150 2011 Platinum model with 80,000 miles on it. I was driving down the road when my gas gauge suddenly started going from full to half within 15 miles. I thought I was losing gas but I wasn"t. The gas gauge went all the way down to empty but I wasnt really empty. The tank had collapsed and instead of having a 36 gallon tank, I now had a 20 gallon tank. There is no recall on Ford F150s for this problem but there is for Focus cars.
Ford Focus cars built at the Michigan Assembly Plant from 2012 to 2018 have been recalled for this purpose.”

 

It was recalled on Focus because it caused engine stalling while driving, which was a safety issue.