Low MPG's

[Dwayne614]

Ive had my 2011 sho for a month now and it started at 12mpg average. So I began to feather the throttle and occasionally use the AC. Now it's at 13mpg and it won't go up. What could this be? I don't floor/hoon the car often so I know it's not the way I drive...the car has 106k miles



P.S. I work at the dealership I got the car from and the mechanic said he replaced all the plugs, but it can be possible he didn't because it doesn't say he installed them on the invoice

 

[SHOdded]

What kind of driving do you do (city/hwy/mixed/heavy traffic)? Spark plugs would be the first suspect. Next would be fuel mix, as governed by data from the O2 (air/fuel) sensors. And last most common suspect would be the fuel injectors. If there's no odor of fuel, that's GOOD. So change the spark plugs out. They are probably WELL overdue.

Underinflated tires can also cut into mileage.

 

[krewat]

My '13 got 15 mpgs on a mixed highway/stop-and-go commute. Same thing with my '16.

What kind of driving are you doing? Stop-and-go/city driving? Or highway? If I'm all stop-and-go, 13mpgs is about it.

Also, don't rely on the lie-o-meter - check with hand calculating by filling up, resetting the trip odometer, driving until it's empty, and filling up, and dividing the miles on the trip odometer by the number of gallons you put back in. Preferably using the same gas pump.

 

[ridered74]

Get on a road where you can go 65 mph steady for a mile or two and hit the reset on your mpg calculator once you are at speed. While maintaining that speed you should easily see 25+ mpg's after you press the reset. If not, something is probably wrong with the car. I could easily see 15 mpg or less driving this car anywhere other than the freeway which is 95% of my miles. Even just idling drops the mpg's like a rock.

 

[Dwayne614]

I mainly drive the car to work which is like 3-4 miles away that's pretty much it. I don't smell any gas fumes anywhere so I'm guessing it's the plugs.

 

[sholxgt]

Short distance driving, like your work trips, will always result in poor fuel economy. The car is spending half of the drive in each direction working on getting up to operating temp. I wouldn't worry about there being something wrong.

Like was said above, if you want to test it to be more sure, take a road trip and see how it does.

 

[SHOdded]

Forgot to mention - make sure you go heavy on the throttle once in a while (like an onramp for a highway) to blow the carbon "cobwebs" out. Since gas does not wash over the back of the intake valve, carbon deposits can be problematic. If bad enough, the deposits may need walnut shell media blasting to remove safely.

 

[2013blacksho]

Walnut sell blasting...??? Never heard of that. Do you have to remove the valves or do you do that with it together? Weird.

 

[SHOdded]

You can find videos on the process on YouTube. Done with the valves in place.

 

[marius883]

Definitely do your plugs, I was told mine had been done too, but I didn't believe them. Had my friend help me change them monday, they were the original factory ones and they looked horrible! Now my car runs so smoothly, especially noticeable during hard acceleration, no more rattling sound!
I've also seen an improvement in MPG's of about 4-5mpg's over the past 3 days. Cheap investment, get them done!
Btw, Autozone has a promotion, if you buy 4 or more motorcraft sparklugs, you get a 10$ gift card!

 

[Dwayne614]

Guys these Plugs are "brand new". I knew I was being lied too. Should I avoid driving until they're replaced? Manual says change them at 100k. I'm at 106k

 

[marius883]

Guys these Plugs are "brand new". I knew I was being lied too. Should I avoid driving until they're replaced? Manual says change them at 100k. I'm at 106k

The same thing the service manager told me, replace them at 100k lol. After replacing mine at 79k I definitely wouldn't wait that long. I will be replacing mine every 20-30k

 

[SilverSH0]

Turn the plug around so we can see the electrode. But honestly, that plug doesn't look that bad from that picture.

 

[SHOdded]

X2. The point doesn't seem to be worn at all.

 

[Dwayne614]

They look a little off to me. I'm guessing I should go based on the electrode?

 

[SilverSH0]

They look a little off to me. I'm guessing I should go based on the electrode?

That's what I would usually go by for the most part. But from that picture the electrode doesn't look bad at all, the plug really isn't that discolored around the threads (really minor), and it looks like ground wire might be a little bit white (hard to tell in that picture).

Overall from one single picture that looks like a pretty new plug. What does the gap measure? When I changed my plugs at 75k miles the ground wire was physically pitted where the spark would slowly eat it away.

 

[sholxgt]

My first set of plugs with 30,000 miles looks MUCH worse than that. Checked them at 2,000 miles and they looked about like the one pictured above.

 

[Dwayne614]

Did the freeway test and my MPGs went from 13.3 to 13.5

 

[SHOdded]

Did you reset the mpg counter before the test?

 

[Dwayne614]

Did you reset the mpg counter before the test?

No. I didn't know that was possible