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Thread: Can ethanol free gas cause a rich condition?

  1. #1
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    Can ethanol free gas cause a rich condition?

    I drained the tank on the 92 camaro, added several gallons of ethanol free gas, and finally got tunerpro to log for me (the log is attached). BLM is pegged at 108 the entire time, and INT usually bounces between 122 and 128.
    Attached Files Attached Files

    1992 Camaro Z28 5.7
    1995 Silverado 5.7 TPI

  2. #2
    Fuel Injected! steveo's Avatar
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    sure, and you can predict a theoretical difference in trims when switching between ethanol blends.

    i've cobbled together a rough linear equation you can use (-0.057*ETHANOL_BLEND)+14.7 to derive a rough target AFR for a particular ethanol blend

    then divide your old target by your new target to estimate a difference in trims

    lets say you were tuned to a perfect 128 trim while using 10% ethanol blended fuel, that means your fueling calculations are aiming for burning a ~14.1:1 fuel

    now you switch to fuel that burns about ~14.7:1 but keep the same fuel maps

    that's about a 5% difference, which would be 'bout ~120 in terms of fuel removed

    if you only have log data you could view this as a 'rich condition', in other words, 'trim is removing fuel because less ethanol means less fuel required'

    lets say you had a 20% blend, that would be about 13.5:1, which is 8%, you'd be more like 118 trim.

    make sense?

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    Yes makes sense, thanks. So ethanol free gas brings the AFR down 5 percent, which should also bring the trims down 5 percent as well?
    You said a 20 percent blend is 8% difference and 118 trim. But if a car is tuned for 10%, and you put 20%, is it not 13.5:1, and would actually increase trim, 4 percent up to 132?

    1992 Camaro Z28 5.7
    1995 Silverado 5.7 TPI

  4. #4
    Super Moderator dave w's Avatar
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    I recently posted the attached document on another thread, perhaps it will be helpful in this thread also?

    dave w
    Attached Files Attached Files

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  6. #6
    Fuel Injected! steveo's Avatar
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    Quote Originally Posted by pro View Post
    Yes makes sense, thanks. So ethanol free gas brings the AFR down 5 percent, which should also bring the trims down 5 percent as well?
    You said a 20 percent blend is 8% difference and 118 trim. But if a car is tuned for 10%, and you put 20%, is it not 13.5:1, and would actually increase trim, 4 percent up to 132?
    yep, if you increase ethanol percentage, it needs more fuel, so your trim number would go up.

  7. #7
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    Sweet thanks guys makes sense.

    1992 Camaro Z28 5.7
    1995 Silverado 5.7 TPI

  8. #8
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    Were you tuned for E10 before? Straight gas does require a little leaning out compared to E10, but it should not be nearly that much of a difference.

    In theory, E10 is supposed to mean up to 10% ethanol is added to the gasoline. Of course, you never know if your local fuel company follows the rules on that.

  9. #9
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    I'm using the factory AUJP bin in the camaro and decided I would put a few gallons of ethanol free gas in the tank just out of curiosity. I also wanted to see how it would log on tunerpro, since I finally got it to work, and no longer have to use a cheap cable and android tablet. But that's neither here nor there. Beforehand, BLM would usually drop a several points at idle, which I assume is normal. Even my new car is like that. But then I filled up on E0, watched trims, and hit 108, and thought maybe there was a connection, and it sounds like there is. Although a drop from 128 to 108 just from E0 is overkill. There obviously must be something else wrong with the vehicle.
    It has 85k miles. The only modifications is a flowmaster muffler and heated oxygen sensor. It did have a hypertech chip in it that I found last week, which is for sale if its even worth anything (I had been driving around with regular, not knowing I needed premium). There is one exhaust leak, about 2 feet before the muffler, a little less than the size of a peanut.

    1992 Camaro Z28 5.7
    1995 Silverado 5.7 TPI

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