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First post here, but I just got back from a 2000 mile trip from North Carolina to Illinois for the holiday. Anyways, this was the first long trip I've taken with the truck (2011 screw lariat, 4x4 3.55's 38k) I was less than thrilled with the way it performed.

First off the mileage left a lot to be desired. I averaged 14.4, most of the time it was between 75 and 80 mph. To accompany the poor fuel economy the truck seemed to be getting slower and slower as the trip went on. It was most noticeable while driving in town, the throttle response seemed to be getting worse and worse. Which I are noticed since I got the truck a couple months ago. I remember it being much more peppy and responsive when I first got it.

I was wondering if anyone had experienced similar symptoms or had any input? Maybe anyone in the Camp Lejune area that might be willing to take it for a drive and see what they think. Really any input would be appreciated. I see how helpful everyone else is here and am tryin to get a piece of it. Thanks guys
 

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Not sure if you're trolling but first your mph killed your fuel mileage. You didn't tell us what size tire you're running. Anything over stock + 80 mph will kill your mileage. Also you left out what the weather was like. Here in Texas we've had that big storm pass through and the head wind is a good 25-35mph. That + 80mph kills your mpg. Also hard acceleration kills your mpg fast. Last I'd take into consideration winter fuel blend change happening now. A few on this forum have been discussing the effects they've noticed on their vehicles. Most see a 1-2 mpg drop. That kills your mpg fast.

. I would also like to know if that was hand calculated or the comp read out.

You could always disconnect the battery for 20 mins and reset the ecu. Then it will stet learning your driving habits.

I'm sure others will chime in here in a bit with some other ideas for you to check on.
 

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If you want good MPG you can't run these trucks that fast. You will find your truck to be very sensitive to speed, wind, & temperature. When you pull something it gets even worse. I can get 19.5 running empty staying at or below the speed limit.
 

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Discussion Starter #4
They're the stock pirellis on it now, not sure of the size. I was mentioning the fuel economy more just to see if it was tied to it acting so sluggish lately, didn't know if the two went hand in hand. I understand they're sensitive over about 70, but I thought I would still see better than 14
 

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Have you changed your air filter ever? It could be a clogged or partially clogged air filter. That over time could cause the progressively worse performace as it gets more and more clogged. Has the performace gotten better now that you are back in the warmer climate? Once you get over 70mph in 6th gear your turbos have to stay spooled up to maintain those speeds. Spooled turbos equal terrible economy.

SPPD
 

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Discussion Starter #6
Haven't checked the air filter, but I can take a look at it when I unhook my battery. From what I've been reading that seems like my best option right now. Maybe a reflash from the dealer as well, seeing as its under warranty. But I don't know if They would reflash given the symptoms?
 

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I realized my reply might be a little late here, but I had the same problem with my 2012 with 3.73 RE and stock tire size. I would barely get 15mpg feather-footing the throttle on the highway. Mileage avg would hover around 14.2 - 14.3 (combined).

I replace the plugs with the motorcraft SP534's and gaped them to 0.030" and wow what a difference. And to avoid the placebo effect, I did NOT reset the KAM memory or pull the battery before changing them (which often time, in the past had made the truck feel as though it was running better). I think these trucks just have a weak ignition system. I hear ford has started gaping plugs at 0.030" from the factory now. Anyway, it's a $40 fix so what could it hurt? You could probably even talk the stealership into doing it for you.
 

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I find a way to see all sides of the spectrum in my truck. If I run 65-70mph to Dallas on the interstate I will get 22-24MPG. If I step it up 5mph I loose 4-6 MPG. I get abysmal mileage in the city (15MPG) if I try my hardest to keep it up. One thin you have to remember is that it requires fuel to make power. as you make more power, you use more fuel. If you are hitting the gas hard to pass people, and merge quickly you are going to loose all mileage. I also see that a short run at hard pace coupled with long runs at light pace don't seem to even out at all, meaning that if you hit it hard you won't be able to make up the MPG's that you loose. Tuning the truck helps quite a bit. I've heard that a catch can does help too, but ultimately its affected by your right foot.
 

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I see a lot of opinions on this matter but very little data. Here is some data:

Pre plug change, AVG MPG: 14.2 +/1 0.1mpg (50 city/50 highway); piss poor throttle response, black fowled up tail pipe, missing hesitation the works.
Post plug change, AVG MPG: 18.8 (50/50); Throttle response much improved, no black smoke on startup anymore.

Only change was plugs gaped [just shy] 0.030"
 

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I realized my reply might be a little late here, but I had the same problem with my 2012 with 3.73 RE and stock tire size. I would barely get 15mpg feather-footing the throttle on the highway. Mileage avg would hover around 14.2 - 14.3 (combined).

I replace the plugs with the motorcraft SP534's and gaped them to 0.030" and wow what a difference. And to avoid the placebo effect, I did NOT reset the KAM memory or pull the battery before changing them (which often time, in the past had made the truck feel as though it was running better). I think these trucks just have a weak ignition system. I hear ford has started gaping plugs at 0.030" from the factory now. Anyway, it's a $40 fix so what could it hurt? You could probably even talk the stealership into doing it for you.
It's not a weak ignition system being the cause to have a narrow gap, it's boost.
Boosts ability to blow out the candles so to speak is pretty high, therefore the narrow gap.
I run an msd ignition, coil and distributer on my supercharged 5.0L, the gaps still need to be around .028-.030 at the most to avoid misfires from blowing out the spark under 14psi of boost.
 

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Fyi: it's gap, gapped, gapping....two p's.

:p
 

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Thread from the dead :

On days when it's over 80 degrees my truck runs really strong after first start and for first few hours of the day then by the end of the day it gets really sluggish.
Even on cooler days my truck runs the strongest for the first hour or so after first start of the day.
 

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Thread from the dead :

On days when it's over 80 degrees my truck runs really strong after first start and for first few hours of the day then by the end of the day it gets really sluggish.
Even on cooler days my truck runs the strongest for the first hour or so after first start of the day.
Maybe due to fuel density???
 

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Maybe? Or heat soak?
Id bet heat soak, Mine seems to be unhappy with the hotter temps coming around. I don't live in a high traffic area and still just cruising around town and at a stop light i am seeing my intercooler temps soar into the 140 to 150 range, once it gets up that high the truck is NOT very happy.
 

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Id bet heat soak, Mine seems to be unhappy with the hotter temps coming around. I don't live in a high traffic area and still just cruising around town and at a stop light i am seeing my intercooler temps soar into the 140 to 150 range, once it gets up that high the truck is NOT very happy.
I think so too man, I also see same intercooler temps, where I'm at there's a **** ton of stop and go traffic, when it gets 105 degrees in the middle of the summer it really sucks.
 
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