I have noticed that when you fill up in gas that the Ford Fiesta's

[Sometimes1needhelp2]

fuel pump acts like it shuts off to early because I will do a battery reset and it always comes back saying I have more gas then I put in why is this ? I mean why do I have to perform a battery reset in order for my gas tank to say I have more gas in there then I actually pumped ? Thanks.

 

[Handy Andy]

Battery reset?

Do you mean pull the battery cable to drain memory and reset the system?

Otherwise, the issue of fuel comes from "static - not moving - stable" state of the sender (float) in the pump assembly reading one level - to another when it's moving.

Then as you drive - your fuel sloshes around in the tank, as it gets used the level drops so it accumulates vapors - the fuel mixes with and acclimates (mixes with) to the older less volatile (if only by fumes and time spent in the tank).

So when you pump gas - the volume of fuels in one temperature is different than in another - so one fuel is warm, another may be colder - so denser - and affects the reading until that fuel stabilizes with what is in the tank - on top of the "static" - stopped your car to fuel - moment onto the drive, those sloshing moments are also affecting the average sampling means to show fuel left in the tank and the mileage calculator it has.

So, in a way, you're seeing one level static, while when you drive the level average appears to change or drop due to the AVERAGING the fuel gauge (in any car) uses to determine the level i the tank - this is done so that when you park overnight - the stabilized fuel reads one level - but changes as you drive due to the movement of fuel in the tank around that sender unit but only by slight amounts so you; are not left to panic - this was standardized years ago by automakers so people that park on an incline were not fooled by erroneous readings in the sender because it measures fuel at one level where the float is.

That can affect the way the tank can be perceived; as being half-full or half-empty - if it's in a corner - that side might be too low or too high and give you a false reading, so they had to standardize the location of the sending unit to get that right level and not let the waves upset the reading too much.

So, remember to pay attention to the number of gallons of fuel you can safely put in - it can't take no more that 12-gals max when fully empty (the Owner's manual says 12.5Gals - but you're pushing it)

Is that the answer you're looking for?

 

[scotman]

He should re state the question. I cannot understand the "what or the why" of his question.

 

[Handy Andy]

Well, to me, The F in the gauge means Forever and the E stands for Eternity.

When the tank is full - you seem like you can drive Forever, but when that tank empties out - it will sit there for what seems like an Eternity until you do something

I read the question as when you initially fill the tank, if not topped off - you fill it but it less than full - it seems to show like there is more in it than when you drive a little way and then it's lower, sometimes much lower.

I work with cars that have been overfilled too many times from other drivers and so it affects their EVAP system - fuel soaks that little filter and it plugs/cakes up - so the fumes never get trapped in there - but if left alone - on a hot day - the fuel tank can bulge from the pressures and the EVAP system can't do much about it.

To me there are several reasons for that change in the fuel needles' settling down moments - fuel, the type of fuel (Premium or otherwise), the weak tank (OEM the overall integrity of the older tank is weaker from the weight and pressures) - and the lack of the EVAP systems ability to handle the fumes as it once did as it was new - to keep pressures in the gas tank stable. Afterall, much of the fuel is recirculated back to the tank - and on hot days - the volatility can make the tanks pressures expand the gas-tank, dropping the level of fuel sensed in certain moments.