Decreasing Gas Mileage

I have an '03 GMC Safari and the gas mileage has been slowly decreasing. Check engine light is NOT on. It was getting around 17 to 18 on highway about 3 months ago. It has 40K on the clock. Gas mileage has now dropped to between 12 to 14 on highway. Any ideas. Dealer told me that the emissions is still under warrenty but that it only covers the CAT and the main computer.

Have a qualified technician scan the system. A good technician will figure out why the mileage dropped. It could be any number of things from a leaky injector or fuel line, fuel pressure regulator, distributor cap, rotor, wires, spark plug(s), MAF sensor, a "lazy" oxygen sensor, just to name a few. Emission control warranty covers far more than just the converter and computer. Any part the computer receives data from, or is controlled by the computer, is considered an emission control part. There are some additions too, plug wires and spark plugs, but they don't want you to know about it for obvious reasons ;) Don't let 'em stroke you.

^ Agree!
If it's an Automatic possibly be your Torque Converter Clutch not engaging. It causes poor fuel economy.

3 Months ago... Is it just from winter gas? I can't get good mileage in any of my cars in Michigan in winter. They just put too much ethanol in the gas around here.

Not sure about other states, but Michigan law requires gas stations to have a label on the pump that tells if their fuel contains ethanol. If it does, the law also requires them to disclose what percentage of ethanol is in each gallon. Very few stations around S.E. Michigan use ethanol in their fuel.

Not sure about other states, but Michigan law requires gas stations to have a label on the pump that tells if their fuel contains ethanol. If it does, the law also requires them to disclose what percentage of ethanol is in each gallon. Very few stations around S.E. Michigan use ethanol in their fuel.
Actually, most stations between Ann Arbor and Detroit use 10% ethanol this time of year.

LM

You're saying "most stations" are breaking the law?

I know I hear all over that using higher octane gas does not really make a difference in economy. Anyone have any thoughts on this??? I know here in Canada, where a block heater is not an option when you buy a vehicle - it comes standard; a lot of gas stations here have what they call "winter gas" where they all have their own secret recipe. I know when that "winter gas" comes out my mileage drops and I start looking at the little 4 bangers until I wake up and realize that I couldn't do half the stuff I do with my van.