Interesting... 2 octane, 5MPG

[BWilliams]

Just a bit of personal experience, but it might save some of you guys money on gas if you burn it like crazy.


I always had used 87 octane since it was cheapest, and I couldn't justify spending the extra money for anything higher. When I bought the truck, I reset the M/C and had been using it to keep an average fuel economy since I got the truck.. 12-13MPG for a highway/city combined economy eek.

Well, while replacing my interior overhead lights with LED boards last Thursday, I managed to short the + and - wires, and blew fuse 15 under the hood, which powers message center memory among other things... so I lost my fuel economy tracking.

I was almost at an empty tank, so I went and decided to pump 89 octane, just for the hell of it (3.159 for 87, 3.259 for 89). Reset the M/C to start collecting an average again, but I noticed that the DTE was showing ~390, instead of the 290-300 I normally get.

Friday, I drove like 210 miles (both highway and city), and my M/C was reading 18.5MPG when I made it home. Gas guage was only at half (normally, a drive that length would put at just about a third)... broad estimates and a bit of math confirm that the M/C is somewhat accurate (210 mi / ~11 gal = ~19 MPG).

I quickly did a little math, and figured out that, by using 89 instead of 87, I actually saved .08 per mile.

Sound reasonable, or was this just some kind of a fluke? I plan to run 89 for a while to get a more accurate average, but this might actually work out to my advantage.

 

[MountaineerGreen]

I'd say it is possible that it could have that big of an effect, I'd run 2-3 tanks, filling at the same place and pump each time to keep the fill ups consistent.

 

[BWilliams]

Thanks for the reply. I planned to test it out a bit more, but I wasn't sure if 5 extra MPG seemed a bit excessive for bumping fuel grade by so little.

 

[MountaineerGreen]

Well, don't rely solely on the Message Center for fuel mileage calculations.

Every time I fill up, I reset my trip odometer. Divide miles driven by gallons used, fuel economy fluctuations can indicate problems, so I check mine every tank.

 

[CDW6212R]

Ditto, like Evan I write down every tank fill up. The mileage does fluctuate a lot depending on conditions. Charting every tank on paper gives you a very accurate estimate of over all mileage. I'm seeing around 13 to 14mpg with my work vehicle in all work use. I have a Scangauge which is far more accurate than the message center, those are awful. My Scanguage is usually within .2 or .3mpg of being accurate on each tank. I'm driving about 73 miles total for work in a day, 29 miles taking almost three hours to drive.

We are all looking for better mileage, keep checking and testing. Good luck,

 

[foxy]

Mate ,Out here in Australia our normal unleaded is 92oct and our premium is 95-98oct .The oct level you have over there per liter or pint is the same as here .Our fuel is based on the Singapore level and it is more refined than yours so that explains the higher oct level and yes it does cost more but much better mpg and also power output is increased as well AND you also get a much smoooother running engine cheers

 

[mab631]

So is their any harm in hurting the engine? Because as far as i understand the higher grade you go doesn't it make it harder to burn the fuel. I have just seen 89 and 92 for like sports car or more expensive trucks. But if it doesn't hurt the engine and you get and extra 5mpg WOW i mean i have a 02 v8 and i get around 12-13 off of the message center

 

[JDraper]

Using a higher octane in a stock Explorer won't get you better mileage. Higher octane does not mean higher gas mileage. It's more likely that your driving habits may have been a little different for that tank. The computer is calibrated for 87 octane and the motor is designed for 87 octane.

To take advantage of the benefits of higher octane fuel, you need a motor that has higher compression so that a denser fuel charge can be compressed and ignited, producing more power. Octane is just a rating of how much fuel can be compressed by the piston before for it self-ignites (this is called detonation). The lower the octane, the easier the fuel self ignites. To keep your fuel prices low, you should use the lowest octane fuel that does not cause the motor to ping (detonation).

Most newer cars have knock sensors that detect detonation and retard the engine timing to protect the motor. If you use a fuel that has too low an octane rating, the computer will pull timing to prevent detonation and thus cause the motor performance to suffer since less timing means less power.

 

[daprez1963]

I would bet that your m/c's memeory by being reset had a lot to do with it. I tried some prem 92 octane a few times in my xlt and only saw a mile increase in my mpg. the manual calls for 87 octane unlike our volvo that calls for premium.
i often reset my m/c to calculate my mpg after each fillup and i usely get around 16 average in the city, sometimes it sits on 17.2 after a full tank. It starts out saying I have 390 MTE but usually settles to 340 after i drive awhile.
i didnt have the 05 when i used E85, and will be curious to see how it calculates that. E85 has a 105 octane though I know from past experience, i will get lesser mpg (around 14 in city and 19 on the highway). I have a road trip coming up in july and will get the chance to use regular gas on the way and E85 on the way back. I will let you guys know then.....

 

[studd469]

I wouldn't trust he M/C either. I have found that when your disconnect the battery for a while, the M/C always comes back on with higher DTE. Im just guessing on this but it might have something to do with the fact that the miles per/gal, fuel used etc all resets.

 

[BryanB]

I don't trust octane ratings. R + M / 2 method is suspect in and of itself. R = Research octane, that is the theoretical octane a gasoline is supposed to have. M = Motor octane, the actual octane a gasoline produces as tested on an engine akin to a briggs and stratton. (now that's scientific!) To get the octane rating you see at the pump they simply add the two numbers together and divide by two as the formula suggests. If you ever get a chance to speak with representative from VP fuels as I have, do so...very interesting stuff.

 

[CDW6212R]

The message center in every Ford product made prior to the latest vehicles(I don't know of those), they all suck, to be blunt. The miles driven numbers are accurate, the internal math that is done is very accurate. But the estimation of fuel consumption is very inaccurate in all of them, every single model made. I do not know why that is, but it is true. Ford should have made them all adjustable, my Scangauge adjusts itself automatically through inputing of the actual fuel filled per tank.

Thus any usage of the mileage estimates of Ford message centers is wrong, they are guesses by a machine which is wrong. If you will fill the tank, and then fill it each time, and do the real math, the facts are clear. If the message center estimates 18.5mpg for a tank, the math will really show 17mpg, or 16, or some other lower figure.

No offense intended here, but any monitoring of fuel mileage must be done by actual tank filling, and real mileage calculations. You cannot add fuel without filling the tank, not write the figures down, and then fill the tank once and calculate fuel mileage. That is useless, it does not account for the inability to equally fill the tank, each time. You must compare mileage numbers from many many tank fillings, and average those. Only a trend in mileage can be considered accurate.

Look at the thread that Al Aldive has for his truck. He has done many things to it, the synthetic fluids and PCM programming, exhaust and intake changes have been the best improvements. Beyond those, making a major change is necessary. Changing fuels, compression, or operating systems is the next choice or step. Regards,

 

[E.B. Cornburner]

When you disconnect power due to a battery swap, etc. the message center defaults to a preset value. After that, it bases its DTE mileage on the MPG calculated in the last 500 miles of driving.

It's possible that by disconnecting power to the PCM, it reset itself back to its defaults, which could have been a more agressive advance curve, etc. and by running 89 octane, the knock sensor isn't picking up any pinging, and therefore stays more agressive than if it were running 87 and heard some pinging and learned a milder advance curve.

Just a couple thoughts...We used to do PCM resets before a track day with the Grand Prixs just to ensure maximum advance and power when we were running the highest octane fuel for racing.

 

[CDW6212R]

Very good thoughts Mike, very good. The Fords never had knock sensors before just recently, I don't know why Ford has always been so slow about bringing new technology in production. Just like GM has been bad about avoiding tuned port injection, they made throttle body injection for far too long.

I personally want the latest possible technology, as soon as possible, at least as an option.

Bring on the hydrogen fuel cells, the electric car technology, propane, and biofuels. We need to get the government and oil industry out of the control of the national energy industry. They are the ones holding us back, them and the fanatical environmentalists.

 

[E.B. Cornburner]

I thought Fords always had knock sensors. Back in the days of the EEC-IV systems, when you did the KOER test, it would tell you to snap the throttle to WOT, which at that time it would advance the timing to 30° BTDC, and look for activity on the knock sensor as the engine was quicly accelerated. A false knock sensor code could result if the octane of the fuel was too high to get any spark knock at that amount of advance.

 

[Thelt]

I get around 18 mpg around town in my Explorer. On an interstate trip I get about 23 mpg. I always run 87 octane. I bet your computer restart has more to do with your numbers than your fuel grade.

I did notice a mpg increase when I had by brakes done and a sticking caliper was replaced. I guess it was putting some drag on the drive train.

 

[CDW6212R]

Mike I'm sure that there have been no knock sensors on the EECIV Fords. I know that the 95-01 Explorers have no knock sensors. The later Fords have been turning up with somewhat higher compression, like the SOHC 4.0 is.

I think part of the reason Ford has stayed away from knock sensors is because of their decision to keep the compressions down, and use only 87 octane. GM has been using knock sensors and high compression for a few generations of cars now. That provides better power, fuel mileage, and requires premium fuel. I'd prefer to have knock sensors and higher compression, with premium gas.

 

[E.B. Cornburner]

There must have been on some vehicles with EEC-IV. There's a trouble code listed for it. Code 225- No knock sensor activity sensed during dynamic response test. (i.e. snapping the throttle)

 

[E.B. Cornburner]

i didnt have the 05 when i used E85, and will be curious to see how it calculates that. E85 has a 105 octane though I know from past experience, i will get lesser mpg (around 14 in city and 19 on the highway).

The FFVs calculate the amount of alcohol present in the fuel by looking at the O2 sensors immediately after the PCM detects a 5% or more increase on the fuel level sensor after the vehicle is started. It then uses this to approximate the type of fuel being used. This setup is less efficient than having an actual sensor in the fuel line or tank like GM, Chrysler, and earlier Fords did. It's basically making educated guesses, rather than knowing the actual percentage of alcohol in the fuel. They "dumbed down" the system a bit, but there's less parts to fail too.

You can tell when your vehicle is calculating what it has for fuel in the tank by going to the DTE in your message center, and when you see --- instead of the actual miles to empty, this means the PCM is calculating the fuel in the tank. If you switch from gasoline to E-85, this tends to take longer, and it also goes to a different default DTE mileage for each fuel. They don't recommend constantly changing types of fuel either...Try to run one or the other for at least two consecutive tankfuls whenever possible. It takes a while for the PCM to optomize to each type of fuel.

 

[CDW6212R]

I wonder if the SOHC engines have knock sensors, that 4.0 has a good compression ratio.