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Discussion Starter · #1 ·
OK, as is well known, I recently purchased an 08 Impala 2LT for the flex fuel and AFM. It's first tank of fuel was straight gasoline, which netted 28.2 by the calculator, and 29.2 by the DIC. The first tank of E85 netted 24.3 by the calculator, and 25.4 by the DIC. Subsequent tanks fell to 19.8 (heavy city driving on this tank), 22.7, 22.3 and 22.4 mpg respectively by the calculator, and 20.1, 23.0, 22.9, and 22.5 by the DIC.

Interestingly enough, the last fill seems to have netted a sharp increase in fuel economy. I filled the tank again after work last night, and netted 26.2 by the calculator (26.9 by the DIC). Not to be outdone, the car is sitting outside with 28.9 mpg by the DIC right now. Every tank has been filled with E85 after the initial dealer delivered fill of regular gasoline. I'm not complaining, as these are excellent numbers by any measurement, but I'm honestly curious if the delivery driver to the fuel station didn't put E10 in the E85 tank by mistake. All numbers have been posted driving my typical 55 mph max speed. Also to be noted, that last tank included more use of the A/C than any of the previous tanks since purchase.
 

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Discussion Starter · #5 ·
Or the meter was off on the gas pump and you got more gas than indicated.....
The pumps are brand new, and the current reading is off of the car's DIC. The number's are close enough on all fills between the calculator and DIC, to indicate to me that they were accurately filled.
 

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Discussion Starter · #6 ·
It will bed interesting to see how it does after a few thousand miles of break-in.
Yeah, I'm wondering how much more the mileage can be expected to go up on the 3.9 engine. I have 2k miles on it now. I will be genuinely pleased if I somehow manage to see 30 mpg on the highway out of the car while running on E85.
 

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I dont have the flex fuel 3.9. But do have a 2007 3LT (3.9L) with AFM.
But you asked if mileage could get better.................
In the following pics, the mileage was about 15-16,000 on the car.
I gassed up- and hit the highway. each way was about 110 miles- until we got to Santa Barbara, had dinner and drove back home. On the way there we saw bumper to bumper traffic for a few miles- but overall- cruise was set at 55-60.
I stayed in the slow lane and used cruise. No AC. the return trip was around 9-11 pm or so.
As you can see I was in the slow lane- and had cruise set at 60 MPH.
Also note the fuel level. after about 220 miles I still had that much gas left.
DIC reported 30.2 MPG.
( i had achieved 32 MPG on DIC on another similar trip but had no camera to snap pic)


 

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Do you reset the DIC's average fuel economy every time you fill up or do you let it average out?

My Silverado's DIC is showing 19.2MPG, but I let it average out over thousands of miles. Sometimes I calculate under 19MPG, sometimes better.

I could run my car on coal and get an infinity of miles per gallon of gasoline... would you be impressed? :rolleyes:
Yes, because you could buy coal instead of gasoline. :D

Actually, the ethanol is carbon neutral since the vegetation it was made from absorbed the CO2 that is burning. Gas and coal are "new" CO2 sources that are being released.
 

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Discussion Starter · #14 ·
Do you reset the DIC's average fuel economy every time you fill up or do you let it average out?

My Silverado's DIC is showing 19.2MPG, but I let it average out over thousands of miles. Sometimes I calculate under 19MPG, sometimes better.



Yes, because you could buy coal instead of gasoline. :D

Actually, the ethanol is carbon neutral since the vegetation it was made from absorbed the CO2 that is burning. Gas and coal are "new" CO2 sources that are being released.
Yes, I do reset the DIC every fill. If you saw the spreadsheet I have for this car, you'd immediately realize just HOW obsessive I am over tracking mileage. My original spreadsheet was designed when I owned the '03 Prius.

With the Impala, I track what type of fuel I fill with, mileage by calculator, what the DIC logged for the tank, calculate the percentage of gasoline I used in the E85 fuel, and calculate again the mileage on the gasoline equivalent of the fuel. I also track price per gallon, and how much I paid for the fill. Since I carpool, I also note who's turn it wass to fill the tank.

In another completely seperate part of the spreadsheet, I track lifetime MPG average of the vehicle, and how much money was spent on fuel.
 

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Discussion Starter · #15 ·
To his pocketbook and to the environment, there's little difference.

I could run my car on coal and get an infinity of miles per gallon of gasoline... would you be impressed? :rolleyes:
I didn't buy the car to save money, or to "save the planet." I bought it so I could keep my fuel money in the U.S, instead of have it shipped overseas.
 

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Discussion Starter · #16 ·
I wonder if the computer is adjusting to the E85. Since you are always using E85 and not switching back and forth, the computer may be able to learn that and switch to a proper E85 fuel mapping.
This would be awesome if it is. :cool:
 

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Discussion Starter · #17 ·
22 miles per gallon of E85=147 miles per gallon of gasoline.
Yeah, the car is a damn gas hog at 147 mpg. I like the 174.6 mpg that I logged out of the gasoline equivalent in the last tank of E85 much better. :D

Take THAT Toyota!!!
 

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Discussion Starter · #18 ·
That is interesting. Maybe it's just a fluke?
I know with gasoline, the quality of the fuel contributes to fuel economy. Maybe the gasoline mix in the E85 was better?
Who knows.
I was thinking that, but I'm showing this on the new refill - still on E85:

 

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was just wondering...is there an indication on the dash of when the 3.9 shuts down cylinders?
 

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I wonder if the computer is adjusting to the E85. Since you are always using E85 and not switching back and forth, the computer may be able to learn that and switch to a proper E85 fuel mapping.
If I remember right, there's a sensor in the vapor cannister that determines the fuel mix in the tank and sets the fuel and spark curve. That way, your engine can run on anything from E85 to pure gasoline and you don't have to empty the tank all the way to switch fuels.
 
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