First off, I drive my car hard. Even given the gravity of my right foot, I usually get about 19-20 mpg. However, when it is really cold out (that's below 40 degrees in the South), my mileage goes to 13-14 mpg. - driving the same route, same speeds, and same times of day. I noticed that, when its cold, I would smell gas for a few minutes after I start the car. I figured it might be the cold start injector, so I unplugged it. That seems to have helped with the gas smell, but the mileage is still crappy. It warmed up for a week, and I got 19mpg. Now its back cold and I got about 14.4 mpg again.

Could the colder, denser air make THAT much of difference? I definitely runs alot stronger in the cold, once it is at operating temp. Maybe I romp on it harder than I realize because of the increased performance?

It shouldn't make that much of a difference.

Here is a page out of my FSM (for a zx), that might give you a couple places to check. I'm sure others will chime in with more relevant help.

EVEN BETTER: from atlanticz.ca (great tech reference) the EFI Bible

http://www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

i get the same thing with my jeep, i can get 20 mpg in the summer, and 15 in the winter. it is an older car (1987)

and has a ton of miles on it (more than 330,000), but according to my parents its always done that. i would be interested

to hear the explanation as to why it does this if anyone can explain whats going on.

My 04 dak is doing that as well....

A couple of things come to mind. Here in Colorado they used to add MTBE to the gas for polution reasons. I'm not sure they still do or not I have not seen the stickers on the pumps lately. When the winter season would come around and the MTBE was in use ppl would complain about the fuel mileage.

My next thought is with the cold temps the gas is "Thicker" and we don't get good vaporation... hey it was just a thought..

cold temps + slick roads = spinning wheels, means fewer mpg. just cold temps, i don't know why it would effect mpg unless you idle longer to warm up the car.

Because of the cam I chose, I always let the car idle for a minute or two before driving it, so that has not changed. Once of the things that stood out to me from zbane's reply was the "air temp sensor." I may need to dig up the diagnostic for it in my FSM.

A couple of things come to mind. Here in Colorado they used to add MTBE to the gas for polution reasons. I'm not sure they still do or not I have not seen the stickers on the pumps lately. When the winter season would come around and the MTBE was in use ppl would complain about the fuel mileage.

My next thought is with the cold temps the gas is "Thicker" and we don't get good vaporation... hey it was just a thought..

I believe most places are phasing out or eliminating MTBE which was used as an oxygenate to help the gas burn more cleanly in the winter - to fight pollution. However, they found out it is polluting the ground water and will probably take a billion or more dollars to clean up. A case of the cure being worse than the disease.

First off... This is how's it's been explained to me and it actually makes a little sense.

I am a born and bread southerner, Charleston, SC to be exact! By way of the Coast Guard I now have logged in more than 5 years in Upstate NY. Aside from the obvious reasons of letting the vehicle warm up longer and spinning the tires on snow and ice...... Air:Fuel ratio. The air is colder and therefore more dense requiring more fuel to maintain the proper ratio, otherwise the vehicle would run lean. Every year when winter comes along I too see a decrease in mpg.

My $.02...

Nate