FYI Britt-
You answered your own question. That 10% ethanol is one thing that is killing your mpg. I was talking to a buddy of mine the other day and he said he lost at least 10% in mileage in his Nissan when using gas with 10% ethanol.

 

Johnny Langton is right on about the octane and altitude. I just drove through Utah, Wyoming, Colorado, and Idaho with my 08 and used the 85 octane with no noticeable difference. And talk about planning - I did this trip at the peak of gas prices!

 

That's right, that stuff is garbage. In my town, I have the choice of 87 and 89 octane with 10% ethanol, or 93 octane with no ethanol. It looks like my next truck will be a gasser. I guess I'll take my chances with premium.

 

Yikes, thats a waste. Your truck is designed to run on 87. Running 92 or 93 will actually cause you to loose power and mileage.

My V10 truck notices no difference between regular and 10% ethanol fuels.

 

guys i live in a pretty good sized cit...2nd largest in georgia...but one company (circle k ) is running about 80% of the stations on my end of town. so i have a choice between 10% eth. or sams(wal mart) gas. still trying to resolve the blown plug issue.....been wrapped up with kids starting school.

 

run only what you vehicle calls for.

 

99, v10, f350, dw, 4x4, with 306k miles, I have tried mid grade and 91 octane with and without a tuner. Ditto on save your money. I pull a 10k 5th wheel 3-4k miles per year on all kinds of terrian. 87 octane works as good as anything I've tried. This is a great truck and engine. Engine runs like new. Just changed the belt for the first time at 300K. Changed pluges every 100K, and had to change the coils at about 160K.

 

I've got to run 93 in my 02 excursion, she pings like mad under load
(even a slight hill), the dealer told me back when she was still under warranty that there was nothing they could do...in hindsight I suppose I should have just run regular and melted her down when my Premium care warranty was still in effect.

And I know that the more premium I feed it the worse it gets when its not under load, but with 105K and no warranty I just cant take the chance.

A local shop has a "top end motor vac" that they claim cleans out the combustion chambers pretty good, i may just drop the 100-150 on this soon.

 

I would love to see one of the guys with major pinging problems take their truck to a shop and get some custom dyno tuning done. I'd be interested to see whats going on with the vehicle during pinging and what can be done with tuning to help get rid of it.

I had pinging problems on my 74' F-100 until I installed the headers and upgraded the ignition components. Never had problems with pinging on my V10 yet, of course the carbon doesn't have much chance to form on my truck as I work it out on a regular basis. Keeping the MAF cleaned is vital also.

 

I have a suspicion that there are many knock sensor failures out there that are the cause of these pinging issues.
JL

 

I usually run regular, but find that not all regulars are created equal. Check my thread earlier about doing something I shouldn't have. I ran premium pulling that load and didn't get one ping up the heavy grades. So I guess it depends on where you are buying and what you are hauling.

 

I have an 01 Mustang GT 4.6L modular racecar. The motor is STOCK as required by our ruleset. Stock compression, everything, 62k mile factory motor. Very simular in design to most Ford modulars like the V10.

I run premium in it on race days to prevent detonation since it's ran at WOT most of the time.
Now, we have to dyno our cars each year. Some years I've ran 87 and some I've ran 91. Every time, the results are within 1-2 HP at 250ish to the rear wheels with neither being the dominate "more power" run with 87 or 91. No difference in STOCK configuration. Period.
That being said, the slower burn, more carbon build up "should result in less power" certainly doesn't show up on a dyno over a 4 year period.... YMMV.

My $0.02: run regular if your not towing. 89 or 91 if towing. Even though you have a knock sensor, why wait until it "knocks" before it gets adjusted? So when towing, why not put in 89 or 91? At $4.00 a gallon and Premium is still only about $.20 cents a gallon more.
25 gallons x $3.8= 95
25 gallons x $4.0=100
$5 difference WOW
Hell, a bottled water and a snack will probably cost you that much...

OT: Remember when gas was $.99
Regular $.99
Mid $1.09
Prem $1.19
That's a 20% difference

Weird that the gas is still, for the most part, only $.10 difference in grades. Dollar for dollar, you pay less now for mid-grade and premium than ever before.

Then 20% difference
Now 5% difference

YMMV

 

While I agree with your reasoning and methods of testing-there IS power to be gained with premium fuel if you adjust the spark table for the increased octane. The OEM tune can be manipulated to run better on 87 with less detonation by doing things to the knock sensor functions and fuel mixtures that the EPA won't allow the OEM's to do.
JL

 

From the Ford owners manual:
----------------------------
Your vehicle is designed to use “Regular” unleaded gasoline with an (R+M)/2 octane rating of 87. We do not recommend the use of gasolines labeled as “Regular” that are sold with octane ratings of 86 or lower in high altitude areas.
----------------------------

I don't know why, but there it is. By the way my 97 Dodge Ram 5.9L V-8 runs fine on the 85 octane stuff up here in Sidney, Nebraska 4300 ft. altitude.

John Katos
2000 F-350 6.8L V-10

 

When towing on hot days, I find the cyclic pattern of knocking/not knocking to be annoying when running 87. With 89, no knocking. So I run 89 when towing.
As GT4.6 pointed out, 89 is only 2.5% more expensive than 87 these days. I have to wonder how much mpg increased when the ECU doesn't have to retard the ignition on 87.... Obviously too little to measure in real life. But theoretically, at least a bit. Maybe 2.5%?