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Another 6.2 for 5.3 swap going on.

Discussion in 'Engine & Drivetrain' started by PatDTN, Nov 9, 2020.

  1. PatDTN

    PatDTN Full Access Member

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    Today's update. I had AAA take my Tahoe to Lethal Performance in Morristown, TN who did the preliminary tune with just the computer. Checked with them later and they've had it running and idling and I think they even drove it into their secured parking.

    Hopefully tomorrow they'll call me to come get it. They're going to tune it for the 93 octane. Later when I can I will see if I can run E85 and get it retuned for that. I'm hoping (someone let me know) that both programs can reside in the computer and it'll switch between them based on E85 detected like stock does. Also, being cheap it wouldn't be a bad thing if I could run regular which is $0.40 cheaper a gallon.
     
  2. iamdub

    iamdub Full Access Member

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    On the FlexFuel vehicles, I'm not sure they tune specifically for E85. My understanding is that they tune for 93 and the PCM will adjust from there based on the alcohol level it detects ("virtually", but that's a whole other mess of a subject). E85 is rarely, if ever, 85% ethanol. It's actual percentage varies considerably from something like 30s to 70s. Also, what you get on one tank of E85 may not be the same content at the next fill-up, even if from the same store and pump.

    Mine was tuned on 93. I have run E85 since then but couldn't tell a difference in power. The drop in fuel economy was quite apparent, though. Also, the PCM showed the alcohol content to be something like 22%. A tester I bought showed it to be much higher, 60-something percent, IIRC.

    Unless you can reliably get the same alcohol content every time and any where you fill up, I think you should tune for 93 and let the PCM adjust accordingly for what it sees you running in the tank.
     
    Last edited: Dec 3, 2020
  3. PatDTN

    PatDTN Full Access Member

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    Thanks Chris.
     
  4. randeez

    randeez Full Access Member

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    gm flex fuel tuning is actually great and quite reliable - the worst part about it is the "virtual" sensor

    theres a lot more involved than this but in laymans terms:

    gm sets a high octane and a low octane table, this isnt according to what octane you put in the tank - this is if the engine senses knock it drops into the lower octane table for a set amount of time without knock then back to the high table.

    the engine doesnt really care what fuel is in it so long as the appropriate afr is accomplished. it is set up around gasoline, gm does some fancy math to determine how much "e85" is equivalent to gas needed for the truck and is just a sliding scale from 0% to 100%.

    in addition to that there are modifier tables for spark, if the ethanol content is higher the more(or less in some instances) spark advance it allows. there are modifier tables for engine temps, power enrichment modifiers with more ethanol.

    gm (obviously) tunes these tables very conservatively, mostly centered around the average user who just throws e85 in it cause its cheaper. so there is room for improvement

    the virtual sensor is set up to calculate the ethanol content after filling up for a few minute window by monitoring fuel trims. i would notice after filling up with e85 if you beat it the ethanol content would always be higher than if you babied it. the ecm can accept a physical ethanol content sensor, required the sensor to be installed inline, powered, and a pin put into the ecm harness , but its a whole lot more accurate than the virtual sensor
     
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  5. PatDTN

    PatDTN Full Access Member

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    That's pretty cool to know. That'll make a nice little reward for folks looking at this thread. Way beyond my pay scale though.
     
  6. iamdub

    iamdub Full Access Member

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    Can you tune the E85 tables exclusively?

    How is this done- tune it on the strongest alcohol content you can find at the pump?

    When I filled up on "E85", I was under the impression that I should drive normally/civilly for the first seven miles for it to calculate accurately and adjust accordingly. Maybe I should've beat on it. When I saw a PCM-calculated 22% alcohol content with a measured 60-something percent actual content, I decided it wasn't worth it to run E85 for power gains cuz the PCM would only advance the spark tables for that 22%.
     
  7. ls1frc

    ls1frc Full Access Member

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    Id swap to a real sensor if doing e85, its not hard to do. It was a 15hp gain on my cammed G8. Of course the only statiom that offered it around me closed down
     
  8. randeez

    randeez Full Access Member

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    you put in max timing adder you want to add for "full" e85. whatever percentage it reads it gives you a percentage of the adder timing.

    this isnt real numbers: 10* of timing on e85, if you have e50 it adds 5* to whatever your base timing table shows
     
    Last edited: Dec 3, 2020
  9. randeez

    randeez Full Access Member

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    Here's a few of them
    20201203_213431.jpg 20201203_213418.jpg 20201203_213404.jpg 20201203_213348.jpg 20201203_213309.jpg
     
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  10. iamdub

    iamdub Full Access Member

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    Makes perfect sense. Thanks for the education! Now I'm gonna research adding a physical sensor...
     

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