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Discussion Starter #1
So all of a sudden my MPG has dropped and also I notice a slight loss in power.

The car runs perfectly other then the awful MPG and slight loss of power. I'm also not leaking any fuel.

I'm not sure where to start. Spark plugs come to mind but wouldnt the beast idle rough?

The air filter is clean (Just "recharged" my K&N filter not to long ago actually). Oil has been changed recently with some royal purple.

I'm really stumped. Any help is greatly appreciated. Thanks a lot.
 

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I'd change the plugs to start...easy enough. also how do you know the MPG is bad? Have you manually calculated it? If so, what is the difference? Alot of little things add up to a loss, could be the tune, the tires, how you drive, summer gasoline blend, the octane, and on and on.
 

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Well, I fill up my tank once a week. That might not sound bad but I don't really drive it much. Just here and there with in the city maybe once a day.

I drive a Honda minivan for work (It has the same gallon tank as the mustang) that I make deliveries in for at least 3 hours a day and I fill that up once a week as well.

So the mustang sees 10 mins of driving a day and the minivan gets driven atleast 2-3 hours. There is something horribly off here right?
 

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change your fuel filter. i bet its clogged or full of dirt. put some fuel injector cleaner in your tank. this should help
 

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Since you mentioned recharging the K&N, did you allow it to dry properly before reinstalling? I have seen plenty of people either not let it dry or over oil the filter only to have to gunk up on the maf sensor. You can buy maf cleaner at just about any parts store or electrical parts cleaner as long as the formula is plastic safe. Also I would make sure the RP was the correct weight and not something overly heavy.
 

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What actual mpg are you getting? Start fillled, drive it at least half a tank, fill it back up and calculated it that way from the trip odometer. I'm assuming the tune didn't happen at the same time the mileage dropped, but it may not hurt to set it back to stock just to make sure..
 

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Same issue here, I had a thread I started a few months ago on the same issue. Same kinda setup, I did plugs, cleaned maf, cleaned CAI, new wires, oil, fuel filter. Dumped alot of time and money and managed to salvage a few MPG's. I think the summer blend of fuel is killing my MPG, I live near KC and all the fuel I get around here has that issue. But when I am away at school in a couple hundred miles away I get better MPG usually, its either that station or just the current blends, I think the blend of fuels in the summer is an issue. For a tuned 05

You do have to consider the drop in MPG could be caused by the roads your driving on, current speed, temp, humidity, etc. So definitely drive the same route's you did when the MPG was good with the same style and see how you do. I luckily was able to recheck with cruise control on the highway and a long road trip to see my before and after.
 

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I think it's the ethanol gas myself as i found a place within 2 miles of my house that sales ethanol free 87 and 93 as i am only trying my first tank full but i can already see a little diffrents in mpg as my car has 4:56 gears so you can really tell.

I ran into a guy that was fillin up his range truck and 3 gas cans.. he told me that he got alot better mpg with the ethanol free gas but it cost alittle more , but he said it was worth it.
 

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I just filled the car back up and i had 161.1 miles showing and it took 7.2 gallons which came out to be about 22 mpg.. that was 60+ mile trip at 65mph and a alot of city driving/ backroads driving and afew to the floor digs..

I was getting about 16 to 17 mpg combined before swicthing to ethanol free 87 and i added a CAI from AM the cheap $84 kit , i also rebooted the computer and reinstalled the 87 street tune from BAMA.. So that plus 5 to 6 mpg combined .
 
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