Experimenting with E85

[A_Harman]

Sept. 6 fill-up.
6.5 gal E85 @ $3.36
6.8 gal 87@$3.86
Weighted cost per gallon = $3.57
Residual in tank was 57% E85. (1.3 gallons)
Total E85 in tank: 7.8 gal
Proportion E85=50%
Fuel economy of previous fill (57%) was 389 miles/13.3 gal = 29.2 mpg
Adjusted Cost per mile = 15.1 cents

Got a new fault code on the commute home: Intake cam position actuator open circuit. Am I chasing my tail here? Cleared it OK with my scanner. See if it comes back.

 

[Rmay635703]

Intake cam position actuator open circuit

will make you burn more gas if it’s occurring (real or imagined by the car)

You likely have a car that is limited to a half tank of e85, which is my experience is plenty, beyond half a tankful usually reduces performance and makes more heat unless your car is designed for it.

 

[A_Harman]

Sept. 9 fill-up.
13.2 gal 93 @ $4.46
Weighted cost per gallon = $4.32
Residual in tank was 50% E85. (1.2 gallons)
Total E85 in tank: 1.2 gal
Proportion E85=8%
Fuel economy of previous fill (50%) was 348.1 miles/13.2 gal = 26.4 mpg
Adjusted Cost per mile = 15.3 cents

Beginning a series of tanks on straight premium gasoline to check baseline fuel economy.
Intake camshaft actuator open circuit fault code keeps recurring. Bought a new actuator and will install today.

 

[A_Harman]

Intake cam position actuator open circuit

will make you burn more gas if it’s occurring (real or imagined by the car)

You likely have a car that is limited to a half tank of e85, which is my experience is plenty, beyond half a tankful usually reduces performance and makes more heat unless your car is designed for it.

I replaced the intake camshaft position sensor last weekend, and about 5 days later, started getting the intake camshaft actuator codes. Maybe the failure of the position sensor led to the failure of the actuator. I'm not a great believer in coincidence! Regardless, I watched live data on the code scanner when the position sensor code occurred. The engine entered limp-home mode, which I could readily detect because it wouldn't build any turbo boost, and the car would barely accelerate. VERY frustrating. Also in limp-home mode, the spark timing seemed to be retarded about 10 degrees, which would definitely hurt fuel economy.

I don't think my car is limited to a half-tank of E85. The LHU engine is flex-fuel, so it should be able to run on 100% E85. Over about 75% E85 I have been getting O2 sensor lean codes. In the year that I have owned it, I have had electronics failures: throttle actuator, intake cam position sensor, and intake cam actuator. I think the car was poorly operated and maintained by the previous owner. When I bought it, the lifetime average fuel economy was 19 mpg, and the lifetime average vehicle speed was 30 mph. So it was run mostly in stop-and-go urban driving. The trip odometers both read the same miles as the lifetime odometer, so apparently the owner never reset any of the vehicle data monitors. Since I have owned the car, average vehicle speed has gone to 51 mph, and average fuel economy is 27 mpg.

 

[A_Harman]

Sept. 13 fill-up.
12.9 gal 93 @ $4.46
Weighted cost per gallon = $4.44
Residual in tank was 8% E85. (.22 gallons)
Total E85 in tank: .22 gal
Proportion E85=1.4%
Fuel economy of previous fill (8%) was 383.6 miles/12.9 gal = 29.7 mpg
Adjusted Cost per mile = 14.1 cents

Fuel economy is good on the almost-pure gasoline blend (well, almost pure E10), and might have been negatively effected by the cam phasing actuator failure for the first half of the tank run. The actuator has been replaced, and the fault code is gone. Hopefully the new tank will give 30+ mpg.

 

[A_Harman]

Sept. 19 fill-up.
13.6 gal 93 @ $4.24
Weighted cost per gallon = $4.24
Residual in tank was 1% E85. (.03 gallons)
Total E85 in tank: 0 gal
Proportion E85=0%
Fuel economy of previous fill (1%) was 422.5 miles/13.6 gal = 31.1 mpg
Adjusted Cost per mile = 14.1 cents

Very good fuel economy, and got the fuel at a good price. No fault codes for the entire tank run.

 

[A_Harman]

Sept. 22 fill-up.
13.7 gal 93 @ $4.40
Weighted cost per gallon = $4.40
Residual in tank was 0% E85. (0 gallons)
Total E85 in tank: 0 gal
Proportion E85=0%
Fuel economy of previous fill (0%) was 425.3 miles/13.7 gal = 31.0 mpg
Adjusted Cost per mile = 15.1 cents

Good and consistent fuel economy. Probably do another couple of tank fills on Premium, then go back to E85 blends. Would like to get 5-6 tanks for baseline.

 

[A_Harman]

Sept. 27 fill-up.
14.1 gal 93 @ $4.40
Weighted cost per gallon = $4.40
Residual in tank was 0% E85. (0 gallons)
Total E85 in tank: 0 gal
Proportion E85=0%
Fuel economy of previous fill (0%) was 430.8 miles/14.1 gal = 30.6 mpg
Adjusted Cost per mile = 14.4 cents

Still doing well. Battery started acting weak, so I changed it in anticipation of cold weather. The old one had 4 years on it.

 

[A_Harman]

Sept. 30 fill-up.
13.1 gal 93 @ $4.76
Weighted cost per gallon = $4.70
Residual in tank was 0% E85. (0 gallons)
Total E85 in tank: 0 gal
Proportion E85=0%
Fuel economy of previous fill (0%) was 413.3 miles/13.1 gal = 31.5 mpg
Adjusted Cost per mile = 14.9 cents

Getting good fuel economy consistently now. But the cost of fuel just jumped 36 cents/gallon since the last fill. I think the price is going to keep going up and up and up.......
This will be the last tank of my baseline check. Will go back to E85 blends next fill.

 

[LDM]

Filled up again today, did a full tank of E85 this time since I am going on a long distance trip next week and I wanted to see how far I go on E85. Not sure if I will be able to find it on the road when I need to stop so I will probably end up using premium during the trip. Filled up with 25.15 gallons of E85, which tested at 80% on my tester. 75.7% was what I got from the alcohol sensor when data logging. Left over from last tank was .85 at 58% (.49) and 25.15 at 80% (20.12), so total gallons of alcohol is 20.61 for this tank. Fill up cost was $78.91 vs $119.91 that would have been cost of premium, so $41 less for E85 at 35% the cost of premium.

My calculated MPG was 11.03 vs 12.6 on the dash calculator, so 1.3 MPG difference there. My tank before was 10.21 so with the alcohol content around 45-55% at 11.03 is a .82 MPG improvement, not as good as the previous improvement going from 70+% alcohol to 60% alcohol. It will be interesting to see the difference in highway miles for this engine so I will report my finding when I get back on the differences. Expect that on Monday the 17th as I will be back from my trip late on the Sunday before.

 

[A_Harman]

October 5 fill-up.
7.8 gal E85 @ $4.00
4.8 gal 87 @ $4.50
Weighted cost per gallon = $4.29
Residual in tank was 0% E85. (0 gallons)
Total E85 in tank: 7.8 gal
Proportion E85=50%
Fuel economy of previous fill (0%) was 399.3 miles/12.6 gal = 31.7 mpg
Adjusted Cost per mile = 13.6 cents

Returning to E85 blends, and not a moment too soon. Price of Premium was $5.50

Here is the cumulative fuel economy chart for all data taken so far:

Note that this chart is ethanol content and NOT E85 content. It is interesting that the linear curve fit does a better job of predicting fuel economy when extrapolated back to 10% ethanol.

 

[A_Harman]

Filled up again today, did a full tank of E85 this time since I am going on a long distance trip next week and I wanted to see how far I go on E85. Not sure if I will be able to find it on the road when I need to stop so I will probably end up using premium during the trip. Filled up with 25.15 gallons of E85, which tested at 80% on my tester. 75.7% was what I got from the alcohol sensor when data logging. Left over from last tank was .85 at 58% (.49) and 25.15 at 80% (20.12), so total gallons of alcohol is 20.61 for this tank. Fill up cost was $78.91 vs $119.91 that would have been cost of premium, so $41 less for E85 at 35% the cost of premium.

My calculated MPG was 11.03 vs 12.6 on the dash calculator, so 1.3 MPG difference there. My tank before was 10.21 so with the alcohol content around 45-55% at 11.03 is a .82 MPG improvement, not as good as the previous improvement going from 70+% alcohol to 60% alcohol. It will be interesting to see the difference in highway miles for this engine so I will report my finding when I get back on the differences. Expect that on Monday the 17th as I will be back from my trip late on the Sunday before.

It would be nice if I had an ethanol sensor. It might reduce the scatter in my data if I knew what mix I'm actually running instead of assuming the 10% content of gasoline and 83% of E85.

 

[LDM]

It would be nice if I had an ethanol sensor. It might reduce the scatter in my data if I knew what mix I'm actually running instead of assuming the 10% content of gasoline and 83% of E85.

I'm sure there is one on your vehicle, any GM E85 capable vehicle is going to have one to adjust the fueling in the PCM based on the alcohol content. You just need a scanner that is capable of reading it like HP Tuners. The VCM scanning program itself is free to use but you would have to purchase the MPVI2 or 3 to connect to a laptop, which is around $400. And a laptop to use, of course. Anything WIN7 or newer will work just fine.

I also checked and the 13-15 Verano is fully supported, you could also tune it with the VCM Editor program as well if you wanted to spend the money there as well. I plan on doing some tuning to my truck after I get some more data logs with the stock setup (well, stock aside from the stuff I changed to enable E85 but I left everything else stock and used the stock parameters from an E85 4.3/5.3L truck), see if I can get some more power and maybe even mileage out of her.

 

[burgessdg]

That was what I was expecting, but that hasn't been the case so far. Ethanol has lower heat content, but the higher octane allows the engine to be tuned with more spark advance for higher efficiency. So far on 50/50, the fuel economy seems to be about equal, and I'm down ~15% on BTU's in the tank.

I expect fuel economy to drop on straight E85. But the lower price could still make it economical, if I don't mind filling up more often.

Yea, I am guessing you have some error factor in your mileage calculation. Ethanol only has 68% of the energy content of equal amount of real gas. Advance the timing all you want. The math don't add up.

 

[A_Harman]

Yea, I am guessing you have some error factor in your mileage calculation. Ethanol only has 68% of the energy content of equal amount of real gas. Advance the timing all you want. The math don't add up.

Perhaps I could send you my spreadsheet and you can find my errors.

 

[A_Harman]

October 8 fill-up.
6.6 gal E85 @ $3.99
6.7 gal 87 @ $4.49
Weighted cost per gallon = $4.25
Residual in tank was 50% E85. (1.15 gallons)
Total E85 in tank: 7.8 gal
Proportion E85=50%
Fuel economy of previous fill (50%) was 369.1 miles/13.3 gal = 27.8 mpg
Adjusted Cost per mile = 15.5 cents

Thanks OPEC!

 

[LDM]

Yea, I am guessing you have some error factor in your mileage calculation. Ethanol only has 68% of the energy content of equal amount of real gas. Advance the timing all you want. The math don't add up.

There is alot more than just advancing the timing going on in flex fuel vehicles. Spend some time learning about it first before making claims like this.

 

[Overfill]

 

[A_Harman]

October 12 fill-up.
6.32 gal E85 @ $3.90
6.45 gal 87 @ $4.40
Weighted cost per gallon = $4.17
Residual in tank was 50% E85. (1.42 gallons)
Total E85 in tank: 7.7 gal
Proportion E85=50%
Fuel economy of previous fill (50%) was 337.9 miles/12.77 gal = 26.5 mpg
Adjusted Cost per mile = 16.2 cents

 

[LDM]

Well I had a lot of fun on my long distance trip and here is the info to go with it from my truck. Had to fill up twice on the road, each time with 91 premium with 0% ethanol, didn't have any E85 stations that I was able to stop at during the trip. Of course I managed to forget my tuning laptop when I left so I don't have the alcohol sensor info for the trip so I'm going strictly on calculations for the ethanol content.

I had filled up with E85 the week before the trip, had about 40 miles of local driving before the start of the trip on Friday. Went 286 miles before I had to fill up the first time, almost all interstate at around 70 MPH the whole way. I used 22.882 gallons of E85 for a calculation of 12.5 MPG. It cost me $101.73 for the E0 premium at $4.649 per gallon. The alcohol content calculates to 2.36 gallons left in the tank which is about 9.1% alcohol content in the tank after fill up, so around what you expect for premium gas with 10% ethanol content.

Barely had any local driving at my destination, under 10 miles total, everything else was highway and interstate driving. Heading back on Sunday I went 427.4 miles before stopping to fill up a little more than half way home, mostly 60-70 MPH depending on the road I was on. I used 22.909 gallons of premium for a calculation of 18.7 MPG. It cost me $105.35 to fill up again with 91 premium at $4.599 a gallon. The alcohol content calculates to .281 gallons left in the tank which is about 1.1% alcohol content in the tank after fillup, so almost no alcohol left in the tank at all.

I ended up at almost half a tank when I got home at around 230 miles, so if that is 13 gallons used it would be around 17.7 MPG. This is only an estimate of course as I don't know the exact amount of fuel used. Still the difference of 12.5 MPG to 18.7 MPG is about a 33% difference between E85 and premium fuel, which is just about the difference I paid for the local E85 vs the road premium. So it would be a wash as far as cost is concerned here. If E85 would have been available I may have also had to add an extra stop for fuel in before reaching home, so if you are looking at the distance and time premium may just be the better choice (not that I didn't stop multiple times on my 7+ hour trip, neither my back nor my bladder wants to be stuck without a break for that long anymore).

Its also interesting that the E85 ends up going to 33% drop in fuel economy vs premium when driving on the highway. I know my truck isn't exactly fuel efficient at higher speeds since its a giant brick when it comes to aero but the city driving only suffers around 20% loss. I would be curious to see how a 50% blend would work out since that gave me the best fuel economy for the overall cost. Not planning on any future long distance trips anytime soon but perhaps the next time I'll take a couple of E85 filled gas cans with me to make my own 50% blend as well as start out with that before leaving home on the trip.