When I filled full tank, it showed me that I have 287 miles to go. Earlier it alway showed 380 and above and abov 400. In fact when I went to fill the gas, the earlier reading after filling said the I had driven 386 miles on the previous fill. What do you think happend?

In the mean time you may want to adopt the system I have done with my MY98. I reset the trip odometer at each fill-up. I have always had plenty of reserve in the tank when I refill at 300 miles driven. It is annoying but after 7 years I have learned to live with it. My tank contains 23 gallons and I usually have 6 or more gallons remaining at fill-up.

The expense of dropping the tank and having the repair vs the always check before travel the trip odometer has worked out for me. I have learned this process from boating where the fuel gauges can never be trusted.

no year car, nor in what country, nor tank sizes.. ouch.
the early warning light comes on at very low fuel.
so you use that to fill up?, it's not for that, its only for those, that forget ? (city drivers?)
never used 100 miles from a station. oops....
on our cars, it comes on near 1/8 of tank or less. USA (varies by engine class unstated by you.)
First off, the sender is very very crude device, ever see one>? (a spindle of wire forming a rheostat, like in year 1900, brutal simple)
and the is set to 0.2 x gallons, full.(on some)
so 10 gallons would be 2 gallons left.
but like i said its very crude, .
The PCM just watches the voltage there,
and is hard coded to turn the lamp on , at low level. (not precision)

it's only there for folks that forget.
if it is dead, the lamp is just burned out. period. replace lamp.. (key on self lamp self test show that lamp works?)
some swift books show, 7.5Liter of fuel, lamps on.
but be aware of 2 more facts
that pump is fuel cooled and fuel lubricated.
so why GO THERE ? and risk burning up a fully good pump. and a $500 repair bill.

keep it above 1/4 at all times and WIN, I promise !

gas here is $1.63 a gal.. cheap enough to burn....
LOL

Not keeping your fuel tank above at least 1/4 is asking for trouble. The fuel pump needs the fuel in the tank to keep the pump from overheating. Also, its just as cheap to fill the tank from 1/2 to full as it is to fill it from E to 1/2. The benefit is that your fuel pump lasts a lot longer with the pump fully submerged in fuel. If you think keeping the tank at least half full is expensive, wait until your pump burns out.

Check filler neck if ok then a line on top could be broke or loose. Ether way better to drop tank and look.

your car probably needs a code scanner OBD2 they are called - there will be a plug for this somewhere under the steering wheel just above the pedals somewhere - Scan for any errors first before moving on to the fuel sender unit which it could also be - could also be corrosion on wires that run from the fuel sender unit itself causing resistance

Does it stick at about half full? I would fill up, the gauge would show full then after 60-70 mile when gauge should show less than half to a 1/4 tank the gauge still showed 1/2 tank so I'd go ahead and fill it up. Finally, I watched my mileage and when my yellow low on gas light came on I filled it half full. After a couple of weeks I filled it up and the gauge has worked every since.

i would check wires leading to tank sounds like you have a bad connection or possiably a bad ground wire if connection s look good and your getting good ground more than likely you have a bad sending unit in the tank

I had the same problem with my 98 Corvette with 69K miles. Mine did exactly as you described soon after I purchased it in November of this year. I went online and read posts of others with the same problem and how to try and fix it. At 1/4 tank add 2 bottles of Chevron Techron cleaner and fill up with good name brand premium fuel. The Techron cleaner will clean the sulfur residue and other contaminants off of the fuel level senors in each of the left and right hand side gas tanks (C-5's have two gas tanks on either side connected by a transfer pump with each side having it's own fuel level sensor). I did this and so far after nearly 3 tankfuls there's been no recurrence of the problem. However, if this doesn't help then the alternative is to replace some if not all of the components mentioned earlier. I got a $1300+ repair quote from my favorite garage prior to applying the above fix. I'm no mechanic and I may have some of the actual part names incorrect. I hope this helps you out and fixes your problem! BTW, you can also use a full can of SeaFoam cleaner in lieu of the Chevron Techron cleaner. I used the two bottles of Chevron Techron the first tankful and used SeaFoam in the second tankful. I plan to use a bottle of SeaFoam every 3-5K miles to help keep this problem at bay and keep my fuel system cleaner!

First you will need to test your information display located above the rear view mirror. The easiest way to see if it is accurate is the next time you need gas, fill the tank up! Your car holds 17 gallons of fuel, the display should read 17 gallons after a fill up. If it displays anything other than the 17 gallon amount, then your fuel level sensor is bad. If it appears to be consistent with the 17 gallon reading, keep your eye on it for several miles and after a couple of times that you restart your vehicle to be sure that it is in fact reading correctly. If you are convinced that information is consistent with the actual data, then it's much worse......It needs a new fuel pump! Good luck!

fuel pump and float