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Normally when I fill my gas tank all the way the screen on the gauge would say 200 miles until empty. Now it only says 77 miles until empty. The needle is on full and everything. Its as if my tank got smaller. Please help
 

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Air in the tank or a bad sensor. Disconnect the battery for 30 minutes then try it. if that doe not work, try a new sensor. Here's the key question. Does the car go beyond 77 miles?
 

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If the gauge says full and you know it actually is full then don't rely on the mileage computer to tell you how much gas you have left. Go by the actual gauge. The mileage computer can glitch out sometimes and even 200 miles is not right. Even a GT would get well over 200 miles to a tankful and more like 300+ miles. My other Ford(not a Mustang) isn't always reliable like that either and will at times give me wildly inaccurate calculations.
Like Logan541 said it might be due a bad sensor or something or the mileage computer itself.
Make sure the car is full and then carry around a 2 gallon gas can in the trunk for a few days/week just for insurance and see if the car goes for at least 300 miles. You should also reset the various mileage computer settings.
 

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I believe the computer uses its current "average MPG" and the fuel level in the tank to calculate the miles remaining. So if it has a very low "average MPG" it will calculate a very low miles remaining. You might check that before you reset it.
 
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How do you know that? Have you run the car with a full tank of gas until it runs out or at least registers over 300 miles on the odometer?
Forget the mileage computer. Just go by the odometer to test how far it will go. Do as I said in my previous post and report back or you won't ever resolve this.
 

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what does your Average MPG say on the dash?

another possibility: the gas tank has two halves; there is a hose connecting them; maybe that hose is clogged (not sure if there is a pump?) so it is possible that you are only filling and emptying one half of the gas tank . . . I think there are some other threads on here with the details, try the search and hopefully you can find them
 
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My suggestions:
Determine how many gallons your tank can hold when it is almost completely empty. The tank capacity is 16 gallons so you should be able to fill it with 14.5 gallons or more with the tank nearly empty. (This is a no cost diagnostic - just pay attention at the pump).

If it will not fill with this typical volume, you may have the following conditions:
1) some sort of internal restriction in the tank between the two sides - note I personally consider this unlikely

2) the fuel tank level sensor is faulty. I.e., when the gauge reads “Empty” it is still partially full.
This is a little trickier to diagnose - especially if you don’t have a high end scan tool. Nevertheless, any reputable shop should be able to diagnose that easily.

3) the Evaporative Charcoal Canister is plugged or Canister Purge Valve is malfunctioning. In simple terms, these components allows the tank to vent when the car is not running. (If you fill the car with the engine running STOP DOING THAT because the ECU commands that particular valve closed with the engine running). If the tank cannot vent out fuel vapors while being filled, the vapor pressure and foaming inside the tank can be enough to shut off the pump way before it is actually full - especially on hot days.

Any reputable shop can perform an Evap system diagnostic test and should charge you no more than 1 hr of diagnostic labor.

Good luck!
 

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I've had two early 2010s era compact Ford cars as daily drivers that have both given wild and inaccurate miles-to-empty estimates at times. This shouldn't be relied on if you know yours is doing it as well. You should just go by the needle on the gas gauge.
I've found that if you fill your car too often without letting the gas tank get down to at least a 1/4 tank from time to time the miles-to-empty estimator seems to be more unreliable. If you don't reset the trip timer, average MPG, and trip odometer then this also contributes to an incorrect reading on the miles-to-empty reading.
 

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I experienced a similar issue last night, returning home from Baltimore. I experimented with different hose positions until it began to fill the tank. I hadn't had this problem in several years. think my issue is related to the pump.
 

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I experienced a similar issue last night, returning home from Baltimore. I experimented with different hose positions until it began to fill the tank. I hadn't had this problem in several years. think my issue is related to the pump.
The 2005 Mustang had tank filling issues that were initially dealt with early on in production with a redesign of the tank but I do remember hearing of complaints about the filler neck design from the first few years of the S197 not being on enough of an angle and it being installed at the factory at a suboptimal position that made things worse on some cars. I've read that readjusting it that little bit that you can will improve the gas filling.
 
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