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Discussion Starter #1
I have a 2011 mazda 3i touring with about 34k miles, for about a month now I've been getting awful fuel economy, approximately 15mpg city. As far as my driving habits are concerned, I do hit a few stop lights on my way to work, but very rarely go over 2,500 rpm as the speed limit is only 45.

When I first noticed this I thought ok, I haven't cleaned my air filter (k&n filter) in awhile, so I did that. Got my oil changed (full synthetic), made sure tire pressure was good and used sea foam fuel injector cleaner on my next fill up. Car is driving great, acceleration is great but my fuel economy is just straight terrible.

I'm trying to avoid having to replace the plugs/wires, to my knowledge mazda uses plugs rated for 120k and I'm not having any performance issues or start up/idling issues. Other than poor mpg

I have been using nothing but 87 Octane Sunoco fuel for at least the past 6 months and this is the first time I've had any problems. I live in PA, so it has been cold and some MPG drop off was expected, but I certainly did not expect to go from 26ish city down to 15. That's unacceptable.

When I had my tires rotated the mechanic told me they were a tad uneven, fronts were 8,7 backs were 6,6 but I can't see that having such a huge impact on the car.

I called Mazda and the tech told me that it's all computer controlled and there is nothing he could do if there wasn't a check engine light on.

Hopefully you guys can be more helpful than he was. Will provide any other information asked of me. Thanks guys
 

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Try resetting ur computer/ecu. To do so u unplug ur battery under the hood for like 5 to 10 mins.

And ur car is fairly new, no need to use seafoam. It may do more harm than good


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Discussion Starter #3
Ok, I'll give that a try. I had read to always use an injector cleaner with every oil change if using low octane/detergent fuel, would you say that's not the case?
 

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Ok, I'll give that a try. I had read to always use an injector cleaner with every oil change if using low octane/detergent fuel, would you say that's not the case?

Many ppl have there own opinion on that particular subject. If u use high quality brand, for me , I only fill at Shell, bp , mobil and chevron. I fill up about 3 to 4 times a month and out of those time fill up premium once. Ur gunna see alot of ppl gunna say our 2.0 / 2.5 L engine is made to take regular fuel / 87 and no need for premium.

I've used a fuel injector cleaner b4, Lucas complete full treatment. Out of all there other kind, in my opinion it's the less harsher cleaners out there chemical wise.


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Celest Zoom-Zoom
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Dont take this the wrong way. But 90 percent of the fuel economy you get is directly related to you driving habits. Maybe you have something going on just watch how you drive. Im not there im just giving my opinion.
 

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Discussion Starter #6
I couldn't agree more that driving habits have more effect than anything. However, I've had the vehicle for a year and a half and my driving style hasn't changed, I was ok with getting 27 combined, realizing I'm a little spirited with the accelerator. But getting 15 is way out of the realm of my driving habits being the only cause.
 

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This is crazy.. My 2.5 gets a good 31 mpg.. Last tank I got 33.. But that's when I drive civilized.. Else I get 18 n 15...

Your car should not get 15 on a 2.0 engine driving normally.. (No hard accelerations... Stepping on the clutch while driving... Forgetting to shift up or DOWN.. Ect)


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Celest Zoom-Zoom
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Hmmm. Yea my speed gets 23 around town if im somewhat easy. Even if i drive like a maniac in it i still get 18 or so. I cant think of anything that would cause a mpg drop that significant. You dony have a hole in your tank do ya. :)
 

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Something with the ECU?? That doesn't make since if your oil is good, plugs/injectors are clean, and no check engine light. Cold weather should not affect mpgs that much. Try switching gas stations see if that does anything.
 

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Discussion Starter #10
Through thorough testing over several months and many tanks of gas I found sunoco to be the clear winner. I am definitely going to reset my ECU tomorrow and see if that helps. Will report back, thanks guys
 

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Discussion Starter #11
Initial results are positive. After resetting the ECU yesterday morning I got 27 miles out of the first little box in my gas gauge with mixed highway/city but mostly city driving. I was at a half tank, though not sure if it was exactly a half tank or not. Drove it a little harder than I would normally since it seemed to be much more willing to rev into those higher RPM's.
 

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Keep up the good driving with a mix of peppy driving. Keep it smooth, sounds like something real funky was going on with the ECU. I don't think it had anything to do with the way you drove though, but it sounds like the ECU was restricting the car to an "emergency-state" since you make it seem like it's doing better in higher rpms now too. Were the shifts rougher at all (if you have an auto)?
 

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Discussion Starter #13
My gas gauge may have been playing tricks. Second bar only got me about 18 miles compared to the first one getting 27. Going to be filling up my tank within the next few days. Might try a higher octane.
 

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No that's a normal thing. In the summer I got 40 miles before the first bar dropped. Now I get as low as 18 sometimes. The gas tank is finicky. winter gas has a different vapor pressure and it's colder so the pump clicks off earlier and doesnt actually fill the tank. I wouldn't worry. If there's no cel and you dont smell lots of unburnt fuel after you drive I'd say your fine. It's impossible to calculate mpg if the pump clicks off at different spots


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