ajrothm

That engine or ECU have no idea what octane rating you are running...there is not any different fuel maps or anything for different octane. All the ECU/engine does is detect knock and make timing advance/fuel curve changes on the fly. There may also be timing/fuel changes based on water temps and especially intake air temps....They are likely very sensitive to heat and likely pull a ton of timing out to protect against detontation....especially under boost. I wouldnt be suprised a bit if there is built in ignition retard that is boost referenced in the ECU that tells it too pull timing as the boost level increases.... Lots of safety margins built into the tuning on these things, I am sure of that....

No doubt that higher octane fuel will likely reduce the engine's propensity to "ping" (aka. detonation, knock etc etc) and thus reduce the amount of ignition retard and less HP/tq reduction.

The problem is, you NEVER really know what you are getting at the pump....Is 93 oct REALLY 87? who knows..... Or is the 93 youre getting really good quality or watered down junk with no additions? who knows.... Car manufacturers are not going to build/tune a vehicle that MUST live on true 93 octane...they would be filling tons of warranty claims if thats the case. (now new Vettes or supercharged Shelbys etc are another story....I am sure that 93 oct is required but....)

TJPlatinumEB

1. Just like aj said above, there are not two tunes in the PCM. The truck makes timing adjustments based on knock detected and other sensors that will of course vary by octane used.

2. A/C will NOT drop your MPG by that much, if any. The TV show Mythbusters busted that one at least twice on their show and notice almost no difference between A/C being used and not. Here in Austin TX it has been over 100 degrees almost 60 days this summer and many of them being over 105. I've had my truck exactly a month and drive it in traffic everyday. It gets 16.5mpg to 17mpg just like it should under these conditions. It does not vary.

3. There is a setting in your display in the dash that tells your MPG to be calculated based off of towing or off of regular driving. If you change that when you tow and then change it back after you tow, this shouldn't be as big of an issue. I can't remember exactly where it is in the menu's, but I've seen it and seen it mentioned here on this forum as well.

bradseabridge

I don't care what mythbusters "proved" when I run my A/C I get around 14mpg as opposed to getting 19mpg without it on. It's a proven fact to my truck, I ran a full tank with it on just to see how bad it really was.

TJPlatinumEB

Not every single vehicle is the same, so I could understand there being some change, but I have a VERY hard time believing that it's a full 5mpg difference for you. That's beyond acceptable. I could MAYBE see a 1mpg difference at most, but I'd be surprised to see that.

My last truck, 2005 FX4 got 14.6mpg no matter what I did. Highway, city, A/C, etc etc never mattered. I even tried what you mentioned and ran it through a whole tank with and without the A/C and didn't notice any difference.

The crazy weather here doesn't permit me not running my A/C yet, but with the truck being rated at 16/22 and I'm getting nearly 17 with all city driving, I'm pretty sure it's fine.

But again, every vehicle and every truck is different. Nothing is for sure across all of them

truckerdude

I thought that the tow setting that you are referring to was only good for calculating the estimated miles to empty based on towing or not towing. So you think that If I tow I should change this setting to "tow" then when I get done change it back and this will make the mpg readout be more accurate?

I wouldn't think that the a/c should drop my mpg by 2, heck with the amount of hp and torque that it has it wouldn't even know that a/c was on.

Thanks for the input.

150SlickRick

The manual does recommend premium fuel for hot weather and towing (I haven't towed yet). I have run 93 octane for the last 3 fillups and no change, about 19mpg. I've been running the ac full time and a few times while waiting for swmbo. And I have a lead foot. But I've only got 2800 miles and I hear they run rich until about 3k miles and then mpgs improve slightly. We'll see.

TruckLarry

There is an option on the LCD to change to tow mode and back to prevent this.

TruckLarry

5 mpg to a/c? Sorry, but that just ain't right. That would be one he'll of a stiff a/c compressor to do that

reward69

An article I read once stated that on the hwy the a/c didnt result in much if any difference in mpg vs a vehicle with the windows down due to aerodynamic losses with the windows down vs up. Around town driving suffered the most due to the extra energy to excellerate the vehicle up to speed. Even with this there was only a 1.5 mpg difference.

Personally I dont see much if any difference on the hwy just as the article says but I do see about 1 mpg less around town with the a/c running.

HunterSmitty

The cleanmpg guys that tested out the ecoboost said AC running was not even worth noting. They got like what, 32mpg over 5,000 miles or something, so anything that would have hindered mpg, they surely tested.

I also don't see any difference when AC is on. If anything, my mpg has improved due to the warmer temps.