Just after having my 2007 Focus alternator fixed, I began noticing that my car was using more gas than before, according to the fuel gauge. I always put in $20 worth of gas when the fuel gauge goes to the 1/4 mark, and normally it'll read a little over the 3/4 mark .At gas being $4/gal, this is about 5 gallons in the tank. After several such fill ups and going only about 100 miles before hitting the 1/4 mark, I seem to be getting only 20mpg. I recall this car getting at least 25mpg before. I have tried my best to check for fuel leaks along the fuel line under the car and into the engine. I couldn't find any leaks. I suspect the problem is the fuel gauge system. The gauge seems to move down quickly from the 3/4 to the 1/2 mark, stay there for maybe 50 miles of driving, then move again quickly to the 1/4 mark. This gets very annoying since I do not know exactly how much gas I really have in the tank and how far I can go according to the gauge. I have been reading similar problems others have with their Focus but have not yet been able to find a solution to mines. If it means an expensive dashboard replacement, I'll probably leave it alone.

Update from Jun 20, 2012: In trying to fix the low mpg of my Ford Focus, I tried the induction cleaning of the fuel injectors using Seafoam cleaner. I also added Seafoam to my gas tank for several fillups. This effort did not give me better gas mileage. Other people on the web advised changing the air filter and the fuel filter. The air filter didn't need changing on my car, so I only changed the fuel filter. The problem is now solved. I'm now getting much better mpg. Whereas the fuel guage used to drop very quickly from 3/4 tank to 1/2 tank in matter of driving 20 miles or so, it now drops only 1/8 tank after driving 30 miles.

Update from Nov 3, 2012: 11/01/2012 The fuel filter change really did not solve the low mpg problem. It appeared that I was using less fuel according to the fuel gauge, but that was not the case.To check the mpg, I filled the tank to the gas cap, drove the car around 50 miles or so, then refilled the same again and calculated the mpg. Things got worse, I started getting 14mpg. I had a OBD2 reading done on the car, and the O2 sensors were giving a rich fuel mixture condition. I changed the pre-catalytic O2 sensor and my gas consumption finally was solved. I'm getting 24mpg city driving for the last two fillups. And while the gas gauge still gives erratic readings, I'm not concerned too much about that anymore.

I noticed the first time filled up my car that the gs gauge would only show about 7/8 of a tank. I wasn't really worried about it. Now, a few years later I is getting really annoying. I pay enough for gas that when I fill up I want to see that the car is full. The low fuel light comes on at "E" but I have no idea how much fuel is still in the tank. I don't want to run it dry but I would at least like to get a tanks worth of gas on a fill up. I have never taken it to Foed but I might see what they sy before the warranty is up.