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Thread: Ethanol questions - converting non-flex fuel to ethanol

  1. #1
    Lifetime Member BLK02WS6's Avatar
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    Default Ethanol questions - converting non-flex fuel to ethanol

    I have a 2006 Tahoe that is a non-flex fuel vehicle (12587811 OS) and I was looking into what it would take to run Ethanol in it... I am looking at everything from 2 seperate tunes (simplest way), to ways to use the flex fuel OS with a dial or something to blend the tables.

    My first question is that in the flex fuel 2006 Tahoe OS (12605114), it says that it doesn't have a flex fuel sensor... so, how does it know how much ethanol is in the tank? How does the PCM know how to blend the tables?

    Has anyone out there done anything like a dial - I would guess using a pinout on the PCM - to dial in how much ethanol (say you stop and fill up with 1/4 tank of gas still left)...

    or is a retrofit possible - not sure what that entails since the Tahoe doesn't have a sensor...
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  2. #2
    Lifetime Member Chevy366's Avatar
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    Here is a good read; http://forum.efilive.com/showthread.php?13171-E38-Flex-Fuel-On-the-fly-timing-and-fueling-anyone-interested&highlight=ethano


    When you say "you want to run ethanol", I assume you know that most gas now has at least 10% ethanol in it.
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    Junior Member the_red_shark's Avatar
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    I have switched my vehicle to e85 in the last week from 98ron. It is an e40 ls2 in an Australian HSV z series senator. I have had some great help from swingtan,Luis @ APS, Dale @ CHE and others in the EFI users fb group.

    With the e40 there is a checkbox in fuel to enable flex fuel, this is negligent as it does not run a flex fuel sensor. There are a few changes firstly stoichiometric ratio needs to be set per ethanol content of the fuel used, Wallace racing has a lambda/afr converter for all fuels on their site. You will need RC10 for this as previous versions dont have this in e40 tables.

    Next you need to tell the PCM that you are running ethanol as it won't know this. In table b0145 set all % values to 1 as it then forces the PCM to use the ethanol tables.

    That's a start and then go from there, I have not finished have too lean cold idle and a couple of little things. Give it heaps of fuel to start with you can always back off and tune to lamda

  4. #4
    Lifetime Member BLK02WS6's Avatar
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    Sorry - I'm talking E85 here - should have been more specific...

    Does anyone know how a flex fuel OS works without a flex fuel sensor? I understand how all of the tables interact in that OS, but just don't understand how it can work without knowing the blend of ethanol in the tank...

    I would really rather not have to run the tank to empty if I have gas in it and then put E85 in it and push a seperate tune...


    Edit: I read the link above - good read, and it explains how the Virtual Fuel Sensing works in the E38 - so is that how the older PCMs do it too? Does anyone know if there is a pin for "hard" sensing on the older (2006 Tahoe) too?
    Last edited by BLK02WS6; March 29th, 2012 at 11:18 AM.
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  5. #5
    Joe (Moderator) joecar's Avatar
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    A flex fuel OS without the sensor works by looking at the trims over some period of time, I'm not sure of the details.

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    Lifetime Member GMPX's Avatar
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    The tables behind the ethanol estimation are baffling.
    Your best option on an E38, E67 or E37 is to fit a real sensor (even though the price is scary). In EFILive you can tell the ECM that there is a real sensor, but here's the catch, not all GM calibrations had the ethanol tables done. For example, the Northstar engine has blank (or non configured) ethanol tables, so even if you fitted a sensor it still wouldn't work. Most of (if not all) of the GenIV's have the tables all set to go. If you look at the Stoich table and it's not all the same number then chances are GM had the E85 calibrations done ready to roll.
    What is interesting is that GM have starting fitting real sensors to the cars again, maybe the estimation just wasn't accurate enough as emissions get tighter.
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    Ross, BLK02WS6 is looking to do this on an 06 LS1B 1MB PCM, not a Gen IV ECM. I have 0 experience with this type of conversion as there is 1 gas station in all of Seattle that sells E85 (Seattle + surrounding areas is ~3-4 million). So doubtful Ill be working on E85 related stuff anytime soon haha.
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    Lifetime Member BLK02WS6's Avatar
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    So, I wonder if I took the flex fuel OS for an 06 Tahoe (12605114) and full flashed it into my non-flex fuel 06 Tahoe, would it then be a flex fuel Tahoe... Sounds funny, but it seems that is all there is to it.
    GM EFI Tuner
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  9. #9
    Junior Member the_red_shark's Avatar
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    No it would not be any benefit. With ls1 PCM you theoretically should be able to tune it to e85 similar in way you tune to petrol just as a completely different tune. As it doesn't have the flex fuel tables nor the sensor you tune to the specific fuel and as I said above change Stoich ratio to 9.77 (off top of my head) and then go from there.

    Then, use the v2 to store multi tunes then if need be change tunes at the pump.

  10. #10
    Lifetime Member GMPX's Avatar
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    Quote Originally Posted by ScarabEpic22 View Post
    Ross, BLK02WS6 is looking to do this on an 06 LS1B 1MB PCM, not a Gen IV ECM.
    Must read a little deeper next time.
    I no longer monitor the forum, please either post your question or create a support ticket.

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