My '1993 Mustang - (why is my fuel log fluctuating so much?)
 

Can anyone tell me why my fuel log is fluctuating so much on my 1993 Mustang? I haven't changed my driving habits other than I don't drive on the interstate as much because college is out for the summer semester.

I'll take a shot, could be short commutes with stop and go traffic and driving few if any highway miles.
If you feel that a answer is still out there then it would be your car needs a tune up, or the wind has something against you lately. j/k.
Your Mustang may really do well cruising at the highway speeds and suck gas like a professional when city driving.

That's actually a pretty major change in your driving environment. It's basically why cars are advertised with highway (usually better) and city (usually worse) fuel consumption ratings!

Yes, but it was fluctuating before I stopped using the interstate as much.

I am currently waiting on a set of lowering springs I bought and waiting to arrive in the mail. According to the hypermilling list, by lowering the center of gravity, you can get better gas mileage. I hope its true; even if it isn't, though, at least my Mustang will look better.

Mustang you got to look closer at why your mileage is fluctuating, your driving it, or someone is siphoning your gas on a semi regular basis..
No one but yourself can figure it out.
what a question really, and with no background info you want the right answer from a blank equation, its just not possible, your the one with the info, your driving the car in question,how can anyone possible know but yourself, which you happen to not know so nobody will know until you figure it out and tell us. Start keeping track on paper of highway, city miles, and speeds driving, fast highway sucks gas slow highway does not for instance do a mental note if your able and gain some understanding as to how your driving affects your mpg, it is you or that gas thief who is responsible for any fluctuations in your gas mileage.

I noticed in one of your fuel logs that you smelled gas? If that is the case even a slow fuel leak will ruin your Fe, also could be very dangerous. If you havent already find that leak asap!

Mustangwill,

Apart from 1 good fill, I don't see that much fluctuation and that 1 fill could have been an overfill on the previous fill and/or an underfill on the following fill.
You've only logged 5 fills, that's not really enough to see a meaningful pattern.
Let it go for a while ..... then worry:D

Short trips for me return 35-36mpg.

After the car is warm I'll see a 10% gain in town.

Highway trip from startup- 40+
Highway trip from warm- 44+

Addition- Rolling backroads without lights or stop signs return 45+ and I have seen 48 mpg on trips in these areas. My reasoning is lower speeds (than highway) and less or no stopping (vs in town).

LOVE THOSE BACK ROADS!!!!

So, I feel really, really stupid because I have discovered why my gas mileage- as well as other mechanical problems- has been so f'ed up lately. About a month or two ago, I changed the sparkplug wires, and my mother and I were looking at the engine when she pointed out one of the sparkplug wires was justing barely hanging onto the coil pack. So, we reconnected it, and I haven't had any other problems since- knock on wood.

Hope you thanked your mother, that was a nice find. Often when working on cars we can cause our own problems, always a good idea to recheck the work. Also though rare remember it is possible to get a defective new part.
Did you get the lowering springs installed yet?