Exact same except 5.4 and 3.55 LS and I'm getting consistently 20-21 mpg highway depending on the wind and averaging 16 city. I must say I am very impressed with it.

 

I dont believe the message center, mines always about 2-3 mpg better then what I get when I calculate it myself. I just did a 700 mile road trip this weekend and the message center read 20-21.5 the whole trip and when I would top off my tank it would calculate out to 18-18.5 mpg. That was running around 72mph through some hilly roads.

 

It is always off. Sometimes it will read low, sometimes high. Always best to calculate it yourself.

 

I'm at 800 miles now and it is slowly getting better. Avg. 17.9 on the way to work (5.4).

 

My 2010 4.6, 4x4 is getting 18.5 mpg all around driving with around 2,000 miles on the odometer.

 

16.8 to 17.2, each and every tank. Hand calculated.

2010 screw 4x2, 3.55's

 

Same setup, similar mileage. I'm on the 4.6l v3 engine.

One thing I've noticed is mileage seems to be very impacted by elevation. When we go to places with thin air, like Colorado, I get much better mileage. Don't know if that's due to thinner air reducing resistance, or if that impacts the fuel mix, or if there's a different formulation of gas at higher elevation - but I've seen 10%-20% improvement in mileage on the same vehicle with the same driver based on location.

 

I am surprised that the message center MPG display would be that far off. Does anyone have any details on how the MPGs are calculated exactly? I would think its a pretty simple system, a flow meter on the fuel line to keep track of the amount of fuel used and the distance traveled via the odometer. It more like a running average right? It takes measurements every few seconds and averages them out?

 

I see the same behavior here, I live at sea level. But when I travel to NH into the White Mountains (2 - 3,000 ft) it seems I get better mileage, at least with my old '01 F150. I don't have any data points to back this up until I take the new truck camping later this year...

 

The trip computer probably works how other vehicles I'm familiar with work. The fuel injection system knows how long each injector stays open and what the flow rate of the injectors are. Some of the innaccuracy stems from the fact that fuel pressure can vary slightly (affecting the flow rate) and there is a little uncertainty with how fast the injectors open and close. Higher system voltages will make the injectors open more quickly. This may or may not be compensated for by the ECU (by adding in a fudge factor for injector open time depending upon system voltage).

There are many potential innaccuracies so, in the end, the calibrated fuel pumps at the fueling station is the most accurate way to calculate MPG. The biggest potential for error here is the odometer. This needs to be corrected primarily if tires of a different diameter have been substituted. Odometers are generally very accurate on modern vehicles with the OEM tires (even though the speedometers are generally quite optimistic). The two instruments have different callibrations. If you have installed tires of a larger diameter the trip computer will report lower MPG numbers than it would with OEM tires. Some of it MAY be due to more rolling and aerodynamic resistance but some of it is CERTAINLY due to the under-reporting of distance travelled. Best thing to do is to have your dealer re-program the system to recognize the new tire diameter or measure the odometer accuracy over a known 5 mile course and calculate the fudge factor.

After an extended highway trip my trip computer will report 22-24 MPG while hand calculated results show 21-22 MPG. It's nice being able to travel well over 700 miles without needing to hit a service station. For the last 2-3 winter months my truck has been used at sea level, mostly for short local trips (2-6 miles) with a lot of idling around, lots of short trips with a two-horse trailer, hauling brush and very little freeway miles. The trip computer will generally report around 17-18 MPG while hand calculated results show 16-17 MPG (about 1 MPG less than reported).

 

That's normal and the result of two things. The truck has lower aerodynamic drag in thinner air. It simply takes less HP to move through the thinner air. Secondly, the engine is effectively "de-rated" at altitude. The barametric pressure sensor "knows" the air entering the engine is less dense and thus it injects less fuel each stroke. You are still cruising along at the same RPM but with a slightly larger throttle opening. The net effect is slightly more efficiency (while having less power on tap).

 

So I was wondering why you would want to put E85 in your tank instead of regular fuel? It's more expensive and the gas mileage is worse.

 

More expensive? Maybe where you are in SoCal, but over here prices are running $2.70 for unleaded and $1.90 for E85. But it is true that the mileage is worse.

I figured that E85 yields approx. 70% efficiency of Unleaded, and I've bought a couple tanks of E85 when the price is 70% or less of unleaded. I'm currently comparing numbers to see what kind of actual cost/benefit there is. So far, over a handfull of tanks, I'm ranging from $0.1615/mile ((21.853gal x$1.899/gal) / 257 miles) on E85 up to $0.2042/mile ((22.1gal x $2.579/gal) / 279 miles) on Unleaded. 80% of my miles so far have been short trip city driving, but the E85 did seem to yield better efficiency when towing a loaded 6x12 utility trailer.

I'm still working on rectifying the data so that I'm comparing apples to apples.

 

So that would be how a 'tuner chip' could extract higher fuel economy?

Doesn't running relatively lean increase the risk of engine damage. Seems like I remember talk about racing engines burning up as the builders tried to maximize fuel economy by running them leaner.

 

I don't get it. If Ethanol is less efficient, how do the HP numbers increase? Not doubting your comments, just asking for future reference.