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Old 01-13-2011, 09:37 PM   #1
mattmak
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Default "up to 10% ethanol" vs. no ethanol

I'm starting to notice trends switching between a no ethanol 91 and gas labeled as "up to 10% ethanol" - this time 94 octane.

just wondering if anyone else has seen the same type of thing.

1. after analyzing the logs for scaling the MAF, the total correction trend is the same shape for both the pure 91 and E10-94, but the total correction averages more than 1% higher (on the positive side of 0) on 10% ethanol gas.

2. my car is already teetering on the edge of throwing P0420 on stock exhaust, but the P0420 shows up much more often on fuel with 10% ethanol.

To me, this sounds like the car is adding fuel when running on E10 gas - running richer - the cat can't keep up, and is therefor more prone to throw the cat efficiency code.

I also find that fuel economy is slightly better on pure 91 but that observation is not as scientifically formulated as the above in my recent experience.

so, yeah, just wondering if anyone else has seen the same type of thing...

M
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Last edited by mattmak; 01-13-2011 at 10:03 PM.
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Old 01-13-2011, 09:59 PM   #2
nairbmik
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Where I live it's up to 15% ethanol. Complete horse ****.
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Old 01-14-2011, 12:00 AM   #3
naimouasta
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i know nothing of tuning but its something i noticed too. better gas mileage with 91 instead of 93. also i noticed the price difference between 87, 89, and 91 is the same, but between 91 and 93 is a lot less like 2-3 cents vs 10 cents between the other three. i guess they just add some more ethanol to bump the octane.
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Old 01-14-2011, 12:39 AM   #4
BoboTheMonkey
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I work for a C-store chain and they choose if they want ethanol or not. Lots of government red tape to run without, but ethanol does bump the octane. Where I live, they have 87 and 89 the same price due to variation in ethanol levels. The premium is also an octane point higher. You do get lower fuel economy with ethanol due to it not having the same energy potential chemically, but with the higher octane rating you could run higher compression (higher octane is less prone to detonation) which would make it more efficient. So you could get similar mpg with higher compression to make use of the higher octane rating. Hope this helps.
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Old 01-14-2011, 01:11 AM   #5
williaty
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Ethanol has a different stoichiometric ratio than normal gasoline. The ECU will always try to target lamba=1 (stoichiometric) with whatever fuel it's using. To do this with ethanol, it has to add fuel. This is why you're seeing increasingly positive fuel trims as the ethanol content goes up.

If I had to guess about the cat code, I'd say it's because the ethanol burns colder and produces a different mix of exhaust gasses and that's upsetting things.
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Old 01-14-2011, 01:43 PM   #6
bhilly82
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I notice about a 2 mpg loss running E-10 blended fuels, if that help.
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Old 01-14-2011, 01:47 PM   #7
larson701
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For the most part, I believe Williaty is correct. I have experimented with higher blends than E10 and have seen the changes in the fuel trims, consistently a higher positive value with increasing amounts of ethanol.

That said, we have burned E10 for many years and I have never seen any CEL that could be associated with the E10.
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Old 01-14-2011, 01:53 PM   #8
chazly413
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^ Yeah, I've never had a CEL from it.

The MPG is lower but ethanol-added gas is supposed to be a bit cheaper so it should even out.
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Old 01-14-2011, 11:57 PM   #9
formula91
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All US standard US cars are able to run up to 10% Ethanol. I don't know if it's law or not, but it seems to be so. So that cat problem is more likely due to the cat itself.

That being said, there was some research done a couple years back about the composition of gasoline from the pump during certain times of the year or day. The amount of water that's found in gasoline is always very low. But during certain times of the day the water % spikes up and down. I just can't remember when.

That being said, it could also account for "bad gas"
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Old 01-15-2011, 01:37 AM   #10
mrcrawford84
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Ive noticed greater fuel consumption on 10% E as well. Ive dropped by about 3mpg because of it.
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Old 01-18-2011, 10:40 PM   #11
mattmak
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Quote:
Originally Posted by williaty View Post
Ethanol has a different stoichiometric ratio than normal gasoline. The ECU will always try to target lamba=1 (stoichiometric) with whatever fuel it's using. To do this with ethanol, it has to add fuel. This is why you're seeing increasingly positive fuel trims as the ethanol content goes up.
I guess that means that in open loop 10% ethanol content fuel will actually make the engine run lean? if your MAF was scaled on pure gas (no ethanol)...
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Old 01-18-2011, 10:41 PM   #12
williaty
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Well, sort of. The AF Learning function is supposed to take care of that. The fuel learning from Closed Loop is applied to Open Loop as a "best guess" for what might be going on. It's marginally successful.
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