99 - BAD GAS MILEAGE - 14MPG

1999 Pontiac Grand Am

Tiny

stlthriot

December, 19, 2006 AT 9:49 AM

I have a 1999 Pontiac Grand Am SE 2.4L with around 97,500 miles on it.

It hasn't been until about the last 8-12 months that I've noticed something rather frustrating.
While I'm driving my car will get good/normal gas mileage but when I turn it off and come back later, either a few hours or a day, I'll notice the gas has " settled" or seems to have lowered or lost gas. And quite considerably too, sometimes the gas guage notch will have moved down a whole notch.

I've done many thing so far and no improvement and actually it seems to have made it worst. I've done oil changes, oil filter changes and had a new oxygen sensor installed and I think also the spark plugs.

At this very moment I've only driven it about 88 miles (city) and it is already a notch below the 1/2 tank mark. Nearly a year ago it was doing rather well in city and I could go nearly 130 miles or more at half tank.

Does anyone have any suggestions or know of any similar situations on the forum that I can check out.

THANKS!
-Chad

20 Answers

Tiny

bobby71

December, 20, 2006 AT 11:56 AM

Ha I would try to figure out your gas milage with out using your gage fill it up drive 100 miles and refill at the same gas station. Then divide gallons to miles. Just to make sure your sending unit might be getting worn out. And then use a diffent gas station(brand) Cheap Things to do. That car should get 22 city 33 high way. If your mileage is off try getting your fuel injectors cleaned .

Tiny

stlthriot

December, 20, 2006 AT 1:35 PM

And that's exactly the thing, I have been dividing the gas out like that and that is how I am calculating the mileage.

What's involved to get fuel injectors cleaned? Cost?

Tiny

stlthriot

December, 23, 2006 AT 11:09 AM

If anyone else has some tips or suggestions please let me know.
Thanks! : )

Tiny

stlthriot

December, 23, 2006 AT 7:08 PM

K, filled up with gas today and only got about 14.1 mpg (mostly city).

I think that pretty bad in my opinion for a small car.

Tiny

robcet1

December, 29, 2006 AT 10:03 AM

Do you smell any gas at all? Check your gas tank. I am getting the same mileage in my car. Smelled gas, and sure enough I have a small hole in my tank. Losing gas just like you are. Fill mine up full, cheked it a few hours later, and gas needle has already moved. I would check the gas tank, or the fuel line.

Tiny

stlthriot

December, 31, 2006 AT 12:18 PM

Nope, I don't smell any gas, and the odd thing is, it is mainly just between uses and it is always about the same amount even if it is a couple hours between or 5 days, it's just a good notch lower and I don't understand.

I feel that the gas between the tank and the engine somehow gets lost when off/starting? Where does that fuel go (the fuel between the tank and engine) when that happens?
Is it maybe somehow burning extra when started? I don't flood it at all myself so I am unsure.

Tiny

robcet1

December, 31, 2006 AT 4:07 PM

Mine does it too between uses now. Have your gas tank looked at. I'm positive that is your answer. I have never had problems with any vehicles until I have bought a pontiac. We are having the same symptoms, so have your tank looked at!

Tiny

lisaolson1981

January, 5, 2007 AT 9:08 AM

That is so funny that I read this! My car does the same thing! I have a 99 grand am se too. I will go home with plenty of gas. Like under a quarter of a tank. But plenty. The next morning I start it up and the gas light will be on! I just laugh because I have only had my car three months. It just seems that's the way my luck goes.I thought maybe I was losing my mind? If I am, I guess I am not the only one. LOL! Good luck!

Tiny

stlthriot

January, 9, 2007 AT 1:14 AM

It's frustrating because besides this I really like the car and I want to keep it but since I can't figure out what is wrong without paying lots of money to guess and check various parts, I may just trade it in and get something else soon.

It's been the most noticeable for me the past year.?

Tiny

Service Writer

January, 9, 2007 AT 5:04 AM

Let's see if we can nail this down : D

For starters, try an air induction service. I would try what I call an air induction service. There are other intake cleaners, I like to use castle hydroblast. You spray it into a vacuum line such as the brake booster line if nothing else is accessible. Full spray for 3 minutes, stall the engine with it or have someone kill it while your spraying. Let it set for a few hours then take for a short drive in low gear, revving the rpms to help break it up. First use Castle cleansrite to clean the throttle bore. Try to get the throttle plates scrubbed good with a brush, while your spraying. Use a rag to wipe the carbon out between brushings. Seafoam is another good product, but smokes a lot.

The 2.4 is a funny motor. How old are the plugs? When you replce the plugs I like to replace the plug boots as well, seems to be a problem more often that not. Be sure they are gapped right.

Other important factors: : idea: Clean air filter : How old is the fuel filter while we are talking maintenace? : Look at the sticker on your door jamb for proper tire inflation and verify it is right? : Take a look at your front tires-is there any edgewear? A bad alignment will cause resistance.
: idea: Driving habits such as quick acceleration, braking at the last minute after going faster than needed. : Idea: Now htat it is colder, is the car being warmed up longer than normal? : Is the check engine light on : : very important to know.

Post your before and after reults, and we'll go further if needed : D

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