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Hi all,

I used to get around 18-20 miles per gallon depending on the mix of city/highway driving I did. When gas went up near $4/gallon, I started really paying attention to how I drove, was much easier on the throttle, and managed to up my mileage to about 22-24 mpg on average which I was very happy about. Since about mid December (3 tankfuls of gas) I have been going between 180 - 200 miles between fill ups, which works out to about 14 mpg. I have had this car for 7 years and NEVER got less than 280 miles out of a tank. Suddenly I'm lucky if I get 200. The car feels like its running fine. I don't see or smell any gas leaks. No check engine light. What is going on???

Opinions please!!!

Jason
 

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The cold weather used to drop the gas mileage of my 95 T-Bird.

It would go from the usual 22mpg down to 13-15 mpg.

My Crown Vic has this same trait.

Has it been cold down in ole Jersee?


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The cold weather used to drop the gas mileage of my 95 T-Bird.

It would go from the usual 22mpg down to 13-15 mpg.

My Crown Vic has this same trait.

Has it been cold down in ole Jersee?


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i thought colder air is better? i mean thats what everyone seems to say colder is better hence inter coolers and all that fun stuff.
 

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i thought colder air is better? i mean thats what everyone seems to say colder is better hence inter coolers and all that fun stuff.
Colder air is more dense, more dense means more oxygen, and more oxygen means more fuel used. It's good for power, not economy.
 

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Also, winter gas is full of alcohol, to help all the water in it not freeze...

My guess in the bad mileage is probably a combination of things, depending on what you've replaced and what's still original.

If the O2 sensors are over 3 years old, replace them. Yeah, I know how expensive that is, but they can kill mileage long before they start throwing codes. I usually move the fronts to the back, and replace the fronts.

Vacuum lines leaky; anything original is bad by now. Replace. Buy ~5 feet of the three sizes at AZ, cut to length. Be really careful with the fittings, they are unobtanium for the most part.

Clogged EGR passages. This makes a difference in mileage as well; I cleared mine with a long screwdriver and a shopvac... :)

Replace plugs/wires if they're over 3 years old. Especially if the plugs are a type with small center electrodes.

Cleaning the MAF is always the first thing to do if there is any problem with something the computer controls, pretty much.

A slipping transmission or torque converter can drop mileage pretty bad; you would notice that tho. :)

Good luck; my recent solution to this was plugs and wires, and lots of Seafoam.
 

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Colder air is more dense, more dense means more oxygen, and more oxygen means more fuel used. It's good for power, not economy.
ah that makes sense
 

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Winter gas really kills mileage.
 

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I second that. I often take a 250 mile round trip that's 90% highway and average between 26 and 29 MPG for the trip. Last week I made that trip and barely got 20 MPG.

My city MPG usually averages between 19 and 22 in the summer; lately I've been getting closer to 14-16.

Thank you, Mr. winter gas blend.
 

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Discussion Starter #12
Thanks for all the responses. I think I'll be doing some work on the car later today. To answer some of the questions, yes it has been very cold here in NJ lately but nothing different than any other winter, and this just started happening a little over a month ago. So I wouldn't blame it on the gas. About the winter gas, I was under the impression they didn't do that reformualtion any more? I know they used to add MTBE during winter months, but stopped that and replaced it with Ethanol due to environmental concerns. And with the research I've done recently, I thought almost all (if not all) gas here in NJ is 10% Ethanol now (not just in the winter). Its so common gas stations don't even have to post anything saying they are selling gas with Ethanol in it. Apparently many states do this now.
 

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Discussion Starter #13
Found the problem???

OK, I have an idea as far as what is causing my gas mileage decrease. :eek: I actually don't think its a gas mileage decrease at all...I think mid-December my odometer began to not register all the miles I drive. So if I drive 320 miles, my odometer reads 250...so if it takes 15 gallons to fill the tank, instead of coming up with 21.33 mpg I am getting 16.67 mpg. I say this b/c I just went back and looked at all my gas purchases since August, and I'm still driving about the same and still buying gas at the same frequency as I was when I was getting "better" mileage. Soo....

Does this sound like its plausible? If so, what could be causing the odometer to not register miles correctly, or not register all the miles I'm driving?

Thanks again,

Jason
 

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Discussion Starter #16
I really appreciate the responses, but don't want to just start replacing things hoping it might fix the problem. As one of the first posters said, I need to start with the simple things first. As I mentioned, I've looked for leaks and never saw anything...but yesterday when I got home from work, there was about 1/4 inch of snow on the ground, and clear as day there was a trial in the snow behind my car from something dripping/leaking. I took a picture and will try to post later. Funny things is I got down and stuck my nose right in it (haha) and it didn't smell like gas. I'm just going to live with it until the spring and see if it really is the winter gas/weather as some have suggested.
 

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I'm telling you it is the cats. The car is old and they only live for so long. I bet they are the screen ones and are really clogged up. It is up to you how you spend your money.
 

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my guess on the "leak" is water condensation from your exhaust. That is if it has no color or odor. If it's leaving a trail it must be coming off the car pretty steadily so you should easily be able to see where it is coming from.

but yeah start with the small stuff. and if you think the odometer isn't registering you could easily test that. just cruise at 60 mph and see if you went 15 miles in 15 minutes. that wouldn't be my first guess though.
 

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I'm telling you it is the cats. The car is old and they only live for so long. I bet they are the screen ones and are really clogged up. It is up to you how you spend your money.
The last time I worked on cats, the problem turned out to be a dirty maf. :D

This is the last thing I would look into; to test if it is the cats, disconnect the exhaust at the headers, and start it up, (Outside!) and look for a loud but better running car, with a black snowstorm going everywhere from the carbon that would have the manifolds clogged.

Bad cats make the car run bad on top end first, and it gets worse as they clog.


If you drive the same drive everyday, as do most of us, keep track of what the odometer says at the beginning and end of each drive; if you see differences, you know.

Good luck; almost everything I've done to my cars shows up in the mileage first...
 

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I have a 93 3.8L & 91 5.0L. My 5.0 started running rough at idle only in gear and accelerating in park. The mileage also plumetted. After a lot of stress and this site, I put on a new idle air control valve. Solved the problem. Put 200,000 miles on my 3.8L also slowly developed almost the same problem. Weird how similar these engines are. Fuel mileage went to crap and stalled idling in gear and accelerated in park. Replaced the idle air control valve and cured the fuel mileage issue. Neither vehicles showed a code for this malfunction. I get around 18 mpg in my 5.0L and 28 mpg in the 3.8L. A lot of people blame a throttle position sensor, but between my cougars and several other vehicles - replacing the TPS has never solved anything. Good luck with your problem.
 
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