I lived out in washington state for a year then came back to massachusetts, and yes the fuel mileage out on the west coast was ownly in the low 20,s. Now that i'm back on the east coast my mileage has gone back up to the high 20's 26.7mpg to be exact, even in the winter. And the winter has been really awfull out here snow (lots) and it's been cold low 20's day and -4 or so at night. I do wonder about the valve train theory thou. The gas out west is bad I guess. O I drive 70-78mph on the highway and 5mph above average street speed limits, they are suggested speed limits.......

 

I have the same problem. I do mostly city driving, and it is getting -- and has been getting from the moment I bought it in July 2007 -- about 14-15 mpg! That can't possibly be, I'm thinking, but the dealer is of no help. The highway mileage had been closer to 30 mpg, but lately is has been somewhat less than that. If I have been doing almost all city driving, I'm near fill-up at about 180 miles; if I'm doing more highway and city, I'm near fill-up at about 220 miles. This is just horrible for such a small car. Help?

 

Any update on whether this worked? If so, I'll try the same. Mine is a 2.3 Grand Touring 5-dr automatic.

 

anyone know the exact steps to resetting the ECU, by disconnecting the battery and so forth?

I'm not getting such good mileage either, about 280 miles per tank...about half highway, half city. I was going to buy some Pulstar Pulse Plugs over the coming summer and maybe a shortram to see if it does me any good mpg wise. I'll report back if I see a marked change.

 

There are several ways to do it "correctly," depending on how much time you care/have to spend.
The std way is: Disconnect the neg batt terminal and wait 15-30 mins. Reconnect.
The second way is: disconnect the neg batt terminal, turn on the headlight switch, hit the brake pedal a few times, switch on the key, etc... whatever you can think of that may draw power from the ECU itself. Then reconnect.
The third method: Disconnect both terminals and connect them together for ~30 secs. Reconnect and go.
Keep in mind that the ECU will relearn, but based on your driving style and over the course of 100-300 miles. If you drive it like you stole it, in theory it should learn the fuel map that way. If you drive it like a granny, it will adapt that fuel map. In THEORY!!
Frankly, I have all but given up trying to teach the ECU in this car what I want it to learn. Nothing seems to make very much difference and I am getting a little frustrated by the electronic control over the engine/fuel delivery functions.
BTW: If you have a 2.3 w/the slush-o-matic, and depending on your personal definition of "tank full," 280 ain't that bad. With my foot in it whenever possible, I usually fill up around 300 miles and she'll take ~10.25-11.25 gals, or 26.5-29mpg.

 

Can't help with the mpg. puzzle, sorry. But this is important. Using anything other than the manufacturer's specified octane rating will get you NADA in miles per gallon, but it WILL put your catalytic converter operating temperature off optimum and if you make a habit of it, it will shorten its life as well as the life of the rear O2 sensor.

 

For all you nascar fans I just got back from Bristol,TN. I left Little River, Tx. ( 8 miles south of Temple,Tx.) on 3-17-09 and returned 3-24-09. O ya it was plenty noisy at the races. Of course if you'r a nascar fan you know Rouddy won. Back to my milage, 2007 M-3 sedan s touring 2.3L. I used cruise control for about 90% of the time seeing as most of driving was on interstate Hwys. Here's my results. Most freeway driving was at between 75-80 mph. I did use B-12 treatment on 4 of the 7 tanks that I used.

Drove a total of 2510 miles
used-----------79.75 gal. of petro
spent----------145.16 dollars on gas.
AVG MPG-------31.47
AVG Per Tank--358.57
I am very happy with these results. Also I use GTX Syntec 5w/20. Also have auto/man slect-omatic 5speed. Used only 87 octane fuel.Car stock all the way. Two riders+ luggage.

 

OK people I think I've solved it.
The trouble is not your car: it's this forum.
See, what happened is that some of the guys getting bad mpgs. hacked the server for this forum and got the i.d. and E-mail addresses of you guys who USED TO GET good mpg. but don't anymore.

From the data they hacked, they then hacked the servers of your internet service providers, got your street address etc. to hack the servers of the state motor vehicle branch where they got all the details of your car, including the dealer who sold it to you.
Then they hacked the dealer's database and got all the nitty-gritty details they needed, and had a matching set of VINs etc. made up which they put on THEIR engine.

Casing your joint for a while, they waited for their chance, and while you were asleep they yanked your engine, replacing it with theirs.

And now a week or so later, you turn up in this forum bitching about how you used to get 31.4 mpg. out of your engine and suddenly you find you're only getting 22.1.......that's because it ain't your engine, stupid. IT"S THEIRS !!!

So my advice to you people posting good mpg. is to "get out of Dodge" , respray your car, put a chain and the mother of all padlocks around your hood, get a pit bull and keep the dog in the car at night, and from now on, stay off this forum, it jist ain't safe for you, got it ?

It's the only possible solution, and it's so obvious that it came to me when I was casually scanning through these posts while I waited for my medication to kick in.

Happy Apr. 1 y'all.

 

I currently have little over 6000 miles on this 08 Mazda3 S touring H.B.
Bought it new and on the first gas tank got 411 miles or 28 miles per gallon.
This car has a 14.5 gallon tank as it said in the manual.

I use super unleaded (different brands) on this car from day one. ever since that first gas tank, I get 280-286 miles per tank in times when not using AC, and now that is AC season I just got 220 my last gas tank.

I have switched to Regular and Med grade gas, but end up getting much worst results.

I have also used Ethanol free gasoline (super) and after the second tank, I started to see a big difference. at least 30-50 miles increase.

Google for Ethanol free gasoline stations in your area see if it helps.

I also have mixed feelings about factory Good year tires that came with this car and am debating to replaced them with a different brand, as tires are known to be a problem to gas mileage issues.

 

Sorry, but I've got to tell you that your anecdotal results are exceedingly unconvincing and contrary to the findings of combustion science not to mention the laws of physics. For engines not designed specifically for use with Premium gasoline, using fuel anything above the recommended grade is simply throwing your money away. Keep doing it if you want, it's your money, but recommending such to others isn't really advisable.