Hello so i have a a 2009 mustang no aftermarket mods other than intake and flowmaster and im getting 14 mpg... Is anyone else getting such bad gas mileage? anyone have any ideas of how to fix..?Seems extremely low to me..

 

first.
Fuel Filter
Run a bottle of lucas oil treatment
flush that tranny if your at 50k
Clean Throttle Boddy
Pump up your tires (accurately)
Maybe you need a balance?
Buy a tune if you dont have one with that cold air intake
I recommend vmptuning.com
clean your maf its probably dirty
flush differential if this all doesnt work.
Then i would check sparks and wires asap

 

The '09 4.0L 5 speed is rated at 17 city and 26 highway. EPA estimates tend to be conservative. I do mostly highway and I'm getting double what you are out of my '06 which has similar EPA ratings. You can take IvanRad's suggestions to make sure it isn't mechanical, but driving conditions and driving style play a big role as well.

 

What kind of driving are you doing? if you're gunning it redlight to redlight that seems perfectly accurate.

Is it driving alright? any hesitation or weird noises?

Follow Ivanrad's plan above, and if that doesnt work heres more to check:
-if your intake was used, clean the filter and make sure there aren't any leaks
-might not hurt to check trans fluid and flush (depends on miles)
I pulled a few mpg out of mine from a spark plug swap too at 60k miles

 

The onboard should be reset at each fill-up for starters.

Secondly, if your speedometer is off (i.e., gears changed or tire O.D. changed without adjusting the PCM) then it'll throw your onboard's calculations off as well as your hand calculations.

I'd do those items listed in IvanRads post above but I'd also run a can of SeaFoam thru the gas tank in addition to the Lucas oil treatment. Both are very good products.

Average fuel mileage is very variable from one driver to another, even under similar conditions. Also, the higher the ethanol content of the fuel the lower your miles per gallon will usually be.

 

Thanks for posting this, 2006 GT man.tranny, 162k miles. Have always averaged 25-27 mpg until the past 2 months, now down to 23-24 mpg and curious what could be the problem. Have done all of the above recently(150k miles) except flushing the tranny / differential and new wires.

 

If this just recently happened, it's possible that some or most northern gas stations have begun using their winter fuel mix. It typically equates to poor fuel mileage and/or drivability problems.

 

That crossed my mind but over the 7 yrs I have had the car I have never noticed a drop-off like I am experiencing now. The car has always consistently given me 25-27 mpg under normal driving. Really is an insignifcant drop in mpg but was curious if I was overlooking something that might be causing it. Car is as peppy now as it was when new, tho I don't kick it in the **** as much as I used to. Appreciate your thoughts on this, Nuke, thanks.

 

id get a compression test if all else fails.

 

...and don't forget that your tire pressure drops about 1 PSI for every 10 degree F drop in ambient temp. If you set them at 30 PSI in 70 degree weather and now it's 10 degrees, you've lost about 6 PSI which can drastically affect fuel mileage.