Terrible Gas Mileage

Hello,
Since about December i have been getting aweful gas mileage. I mean really bad, about 15 miles to the gallon at best. I have filled teh tank more than once and from different gas stations.
The dealership have changed the Air filter, Oil filter, Cleaned the injectors and ran it " on the computer" and nothing out of the ordinary has shown up
The car runs fine and does not sound different and i have not had a drop in power. The tires are fine and i dont feel any shaking from the wheel.
I have worked on cars for years but this one has me stumped, can anyone help?
I can answer any questions you want
Thanks

Welcome to the forum!

I have a silly thought - could you have a fuel leak somewhere? That would squirt the fuel out on the ground, obviously reducing mileage.

If you are parking in a garage, I would assume you would smell gas fumes, if there was a leak. But you never know. Maybe it only leaks under pressure.

Just a thought.

One other question: Are you using the on-board computer to calculate the mileage, or doing the calculations yourself?

Take Care,

Hi,
thanks for your reply.
I have checked for leaks, i cant find any before or after the fuel pump. I also dont smell any gas. I wish this was just a fuel leak and i could fix it, it is so frustrating.

I have been calculating the fuel milage myself i dont have a computer in the car. I filled up, reset the trip meter and the emptied the tank. Then worked out the milage.

Any other ideas?

Perhaps the oxygen sensor is bad, but is functioning well enough not to trip a code? Otherwise, perhaps the injectors are dribbling fuel (?).

Just trying to think of things that would affect fuel mileage but would not trip a code....maybe other posters have ideas....Glen

A general tune up could be in order.

Ours has 62.5K miles on it and I checked half city driving, half road driving and it got 26 MPG. I don't pet it and don't gouge it, normal senior citizen driver with a little heavy-foot. :wink: Runs like a striped ape and no complaints about performance.

The O2 sensor is definatly something i will be looking at. The local Cheve dealer has offered an hour of "diagnostics" this week as they have not fixed the issue yet.
Please give me any suggestions you have for them to look at.

Thanks again

"Please give me any suggestions you have for them to look at."

Apparently something, (a sensor?), is feeding your ECU, Electronic Control Unit - (the brain), computer incorrect info. Please read this link then you'll understand what I mean about what an important part the many sensors play in engine operation.
http://autorepair.about.com/cs/fuelinjection/a/aa030301a.htm
Thing I don't understand is why the computer isn't storing a code(s) telling them what sensor is bad.

Look at the bottom of page 3: " While these sensors can, and do, go bad it's important to always check the basics before condemning a sensor. You have to look at the connectors and make sure they are clean and tight. A loose or dirty connector can cause the same symptoms as a bad sensor."

Any chance they have one of those things they stick up the exhaust pipe and measure the emissions? It would be running *real* rich and inside the tailpipe should be black as soot. You didn't say how many miles on it but Chevy says no spark plug change until 100K miles. Service writer here says they see them with 125K and more miles on the original GM plugs and engine still running fine. Naah, something wrong there that an ordinary tune up won't cure.

The link explains it and if the Chevy tech can't find it I'd ask for the name and phone number of your area Chevy factory representative because 15 MPG is absolutely ridiculious and certainly causes much grief to your budget. 15 MPG almost sounds like you're driving with the emergency brake on. . . .

Is the transmission doing it's job correctly? Do they have a portable tachometer they can hook up and see how many RPM's the engine is turning while you drive?

Some good, "food for thought," reading in this link: http://www.2carpros.com/topics/fuelecon.htm