Terrible Mpg and Fuel Gauge Moving Side To SIde

What Can be The reasons for the problems Im Having On My 93' Buick Lesabre . 20 dollars gets me about 7 gallons ( i use 89 ) . the gas will last me about 115-120 miles . shouldnt it last longer? and its mostly highway miles but i do have some city miles too. also the fuel gauge is constantly moving side to side. hard for me to tell when i need gas. sometimes its up, 1 minute later it'll be down like i need gas :banghead: any help?

Your car is actually getting better mileage than mine; mine used 4 gallons after just 64 highway miles! There are many things to look at, when was your last tune-up? Fuel and air filter changes, tire pressure, a/c or other electrical devices such as the rear defogger, thermostat stuck open, and even your own driving habits, gunning the pedal vs. babying it on accelation....
Also, check your vehicle for codes, there may be a clue there too.

As for the fuel gauge, the sender unit is connected with the fuel pump inside the tank. Mine fluctuates as well, but not too badly.

First, you need to find out what your MPG is. Next time you are at the pump, reset your trip meter and fill the tank. after a hundred or more miles, refill the tank and divide the number of miles on the trip by the number of gallons. You should get around 18 for city driving, and around 28 for highway driving. If you do a little bit of both, then you should have a number somewere in the middle.

The fuel gauge is probably caused by a faulty fuel sending unit, but its possible that the guage itself is faulty.

I agree with Loekee75, driving habits and plugs, wires ect. can have a big effect on mpg. The gas gauge thing, its a GM it has a Floating gas gauge.
Stoped on a level surface is the only true reading!

Roughly that puts your average mileatge in the 16.43 MPG range. Definatley some routine maintanence checks would be in order.

One thing not mentionded here, I always kept my PA in tune and all the sudden I noticed a 4 MPG drop after my wife used it for about a month. After driving myself batty thinking about it, I opened the normally near empty trunk to find a good mass of "garage sale goodies" weighing it down. :disappoin