Why am I getting bad gas mileage?

Question

I just got a 96 Pontiac Grand AM SE 3.1L and the gas mileage is deplorable. The person I got it from never maintained the car so there are a number of fixes. Could it be a fuel pump, fuel filter, or sensor, and how do I check that? To help out It takes about 30 dollars to fill it up, So I figure it's a 10 gallon tank. sometimes I can literaly see the needle move two ticks just to go 15 miles and then sometimes it will look like I magically have more gas in the tank cause the needle will move back up a whole tick.

Answer 1

The gas gauge is anything but a precision instrument. Fill the car all the way up and record the odometer reading. The next time you get gas, fill it all the way up again and record the odometer reading again. Now you really know how many miles you drove and how many gallons of gas you burned. Dividing will give you the miles per gallon and you can compare that to the EPA estimates for that year and model to see if you're really getting lousy gas mileage.

Don't expect to get the actual EPA estimated mileage, though. Their estimates are based on emissions testing, not on actual gas consumption.

There are a number of things you can do to improve gas mileage, including changing the air filter, making sure the tires are properly inflated, and removing extra weight from the car (i.e. the 80 pounds of stuff you've been meaning to clean out of the trunk.) See the article listed below for more tips.

Answer 2

Reasons For Bad Gas Mileage

Answer 3

Poor Gas Mileage

Answer 4

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RE:
Why am I getting bad gas mileage?
I just got a 96 Pontiac Grand AM SE 3.1L and the gas mileage is deplorable. The person I got it from never maintained the car so there are a number of fixes. Could it be a fuel pump, fuel filter, or sensor, and how do I check that? To help out It takes about 30 dollars to fill it up, So I figure...

Answer 5

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What kind of service plan are you on? Do you get your injectors cleaned? Are you running a stock air cleaner or an aftermarket oily? Are you getting any check engine lights that will go out on it's own? Since you changed the plugs, I am assuming your were smart enough to change the air filter too. My first thought would be to put a clean O2 sensor in the exhaust. That's the one that monitors your engine fuel mixture during driving.

Answer 6

First, a complete tune up (plugs, cap rotor, wires, air filter, pcv valve, breather filter, fuel filter, etc.

Second, check tires for the proper size and that they are properly inflated.

Third, change the engine oil and use a good grade of 10W30.
And don't get chincy with the oil filter. Use a good filter, not some no name.

Forth, have a mechanic run the computer systems for any possible fault codes. If there is a serious problem, the ECM will run the car in "default mode" until the mechanic hooks up the computer to determine whats wrong, repairs the problem, and resets the computer.

Fifth, run an emissions check. If the catylytic converter is partially clogged, it will also cut back on performance and the mileage will decline.

As for the fuel gauge, it may just be some bad wiring between the tank and the dash. Also if memory serves me correct. that car came with a sixteen gallon tank. Look for a dented tank.

Answer 7

ok, many things can cause bad gas mileage. The easiest to fix is a tune up, spark plugs, wire, air filter, fuel filter. Other things can be brakes draggin, fuel pressure high, bad oxygen sensors, u said it's a 96, is the check engine light ON ? please be specific, Im a mechanic wantin to help people but the questions should include, year make mode, automatic transmission or stick, check engine light on or off? car runs at normal temperature? 1/2 gauge?

Answer 8

Take it to a mechanic who can put it on a computer. Those computers can tell you every single thing that is wrong with the car.

Don't buy any of those gizmoos to improve gas mileage. Myth Busters did a test on several of them that they purchased on the internet and none of themimproved mileage. One, in fact lowered mileage by 10 mpg.

Answer 9

Before anyone can answer they would need to know what your gas mileage is, maybe it is not "deplorable" for this car. Most likely it is the nut holding the steering wheel, although replacing a clogged air filter could help.

Answer 10

If your gas mileage is bad, there are a number of reasons the 3.1 gets that way. There are a handful of things you can check and repair yourself very easily. First off you have a 16 gallon tank. You should get 24 city and 30 highway mpg. The fuel pump and fuel filter are obviously working. Pull your dipstick and see if there is gas in the oil. You may have an injector sticking open. It would help to know if the car has a rough idle, which would accompany all of the other reasons your gas mileage would be poor. With the info you have given, one could surmise that you have a lead foot. You can't rely on the gas guage for your gas mileage. The sender floats in the fuel and guages only give an approximation of how much fuel is really in the tank. You might want to pull the air intake tube off if the car was poorly maintained, open the throttle plate on the throttle body, and see if it is coated in carbon inside the upper plenum. Without more info, all of the other possible causes are unlikely. If you have a check engine light, or a rough idle, or a stalling issue in conjunction with poor gas mileage, there would be quite a few more inspections and repairs you could do yourself, that we could help with.