I've had quite a few Fords in the past years and never have experienced this before. I decided to run tank of 93 octane to see how the truck would do as far as performance and mileage. This being my 1st Ford with a modular motor, I am still learning, but the gas mileage shot up from 15.5 to 18! And I was even pulling a trailer (only a small utility with a washer and dryer). I am going to try this with another tank full of premium and see what happens, but has anyone else experienced this?

 

It is my understanding, that the control module on these newer motors has the ability to sense a better quality of fuel. In so doing, the pcm will advance the spark optimum to the fuel, more efficient burning of the fuel, hence the increased fuel economy. It's not a fluke!

Greenhaw

 

the last time i really filled the truck myself ( i live in new jersey where they pump your gas) i kept going and going till it started to come out of the truck. i guess sometimes when we check our gas milage we are not accounting for that 2 or more gallons that maybe we had the last fill up vs this fill up. does this make sense?

 

Probably. Either that or you modified your driving habits since you know you were running more expensive fuel and drove more conservatively. Try recalculating your mpg using a fill volume of two gallons less than you actually put in.... Fuel calculations should be averaged over several tankfuls to reduce these kinds of errors.

There is no additional energy content in premium fuel compared to regular fuel.

The PCM uses the knock sensor (KS) to monitor for pre-ignition (knocking). It will dynamically advance timing until knocking is detected, then back off enough so the knock goes away. This process is continually updated as the vehicle is driven. It has only a little to do with the actual fuel economy, but a lot to do with how well the engine responds to the throttle.

Steve

 

Could you have gone from an ethenol blend to a straight gasoline? The energy content of straight gas is higher. Shell here in Canada doesn't add any ethenol to their gasoline. So people are seeing better milage with Shell than with the blended brands.

JMC

 

Either you got some gas that didn't have ethanol in it as JMC mentioned or you changed driving habits. Premium fuel has no more energy in it than regular. Higher octane is just a higher anti knocking agent.

 

Ok, thanks guys. I havnt been driving any different though, maybe even on the gas a little more. I'll see what the next tank does just for curiousity.

 

But higher octane fuel has the potential to have more energy through additional compression without the problem of spontaneous combustion...
if that makes sense

 

Then there's always the engine software update... got mine updated the oter day and I'm seeing between 1.5 to 3.5 mpg increase depending on how much city vs. highway

 

Premium fuel , as has been stated above, has no more energy content/BTU's that 87 octane fuels. There is no way to gain more compression in your cyclinder by adding a different octane. no way no how. I wont go into all the things to add comperssion.
The difference in 93 to 87 octane fuel is this. The higher the octane rating the slower the burn time. This is why, with running higher octane fuels, one can advance the timing to compensate for this slower burn time and adding a little more power.

As for the original post, did you use a different brand of fuel? All the other ideas posted may also be a reason for your increase. If you used a different brand of fuel, the energy/BTU content may have been higher in the fuel you used the last time... Just wondering if it is the same brand...

 

I asked the service manager at my local dealer this same kind of question reguarding running lower octane in a new aviator. (4.6L) She told me that running a lower octane would lower performance and mileage. I went through about a 30 minute discussion, but the basic end point was that if you burned higher octane in a truck requiring only 87, the computer would adjust and it would be possible to achieve better power and mileage. From the horses (fords) mouth.

 

Hey 98navi,

Yes what you said is true, and it touches along with what Green1340 has said as well.....

 

I too believe that running a higher octane fuel increases mileage in these trucks. I would constantly get 1+ mpg better on 93 then I would on 87. I did this study for over a month calculating each time I filled up, alternating which fuel I was using. Is it worth it to run higher grade for better mileage? In my case, no.

 

A great engine prophet once said, "One tank doth not a mileage trend establish."

One tank is a blip on the radar. Run it for at least a dozen tanks before claiming exceptional mileage. One tank can be a blip on the overall fuel mileage chart. If the next 10 result in the same mileage, then I'd say we have a pattern emerging for your truck on that one particular brand of fuel from that one particular vendor.

-Joe

 

So, how are the computers supposed to recognize that you are running a higher octane?
It doesnt make any sense to me, if you could get better gas mileage you would think Ford would have suggested you run the higher octane.