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Thread: Flex fuel going crazy

  1. 09-12-2013 #1
    13Sierra6.2
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    Flex fuel going crazy

    I have a 2013 sierra 6.2 did a front mount turbo setup on it bent a rod so it got a forged rebuild. While the motor was out it i also installed a converter in it. Nothing electronic was replaced just unplugged for the motor rebuild then plugged back in. I know have the truck back on the road and the alcohol sensor is reading 64% even though i ran the tank completely empty and put premium gas in it. I even went to a different station today and it only changed to 62%. While i did the motor rebuild the truck sat for 3 months with no battery in it and it know has no cats so i unplugged the rear o2s and just left the SES checked with the codes set to 3. I'm wondering if anyone has ever seen this? Is it from the rear o2s or it just needs to do its thing for awhile im kinda lost truck only has 6k on it everything is brand new. Any help is greatly appreciated thanks
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  2. 09-12-2013 #2
    Area47
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    you will have to get the ethanol content calculation reset. If you have access to a tech2 it can be done. You will have to have less than 3% ethanol in the tank to correctly do the relearn.
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.
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  3. 09-12-2013 #3
    GPGTP
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    Quote Originally Posted by Area47 View Post
    you will have to get the ethanol content calculation reset. If you have access to a tech2 it can be done. You will have to have less than 3% ethanol in the tank to correctly do the relearn.
    Really? How is this possible since pump gas is e10?

    Is this a common problem and why does it happen?
    Last edited by GPGTP; 09-12-2013 at 05:19 PM.
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  4. 09-12-2013 #4
    GPGTP
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    Quote Originally Posted by 13Sierra6.2 View Post
    I have a 2013 sierra 6.2 did a front mount turbo setup on it bent a rod so it got a forged rebuild. While the motor was out it i also installed a converter in it. Nothing electronic was replaced just unplugged for the motor rebuild then plugged back in. I know have the truck back on the road and the alcohol sensor is reading 64% even though i ran the tank completely empty and put premium gas in it. I even went to a different station today and it only changed to 62%. While i did the motor rebuild the truck sat for 3 months with no battery in it and it know has no cats so i unplugged the rear o2s and just left the SES checked with the codes set to 3. I'm wondering if anyone has ever seen this? Is it from the rear o2s or it just needs to do its thing for awhile im kinda lost truck only has 6k on it everything is brand new. Any help is greatly appreciated thanks
    It's not from the rear O2's jake, it's an alcohol sensor, it could care less about that.

    It's either the sensor itself (doubtful), or it needs a cal
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  5. 09-13-2013 #5
    13Sierra6.2
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    Okay thanks for the info i'm gonna get a tech2 soon and see if that fixes the problem.
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  6. 09-13-2013 #6
    wyochimneysweep
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    yeap you got to reset the ethanol content. there is a specific sequence you got to do after resetting it to.
    My setup is a 356ci with a 260/268 (212/218 at .050 lift) duration cam with aluminium corvette heads and flat top pistons running 11.3 comp. ratio. with tuned port injection and vortec crank pick up and dizzy running a 411 pcm and 60lb bosch injectors, 1.6 ratio roller rockers. For transmission its a 4l65e built with the monster in a box mega ss kit. All in a 92 chevy ext cab 4x4 pickup with a 98 cab now installed with a third door! running only e85
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  7. 09-13-2013 #7
    Area47
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    not driving the vehicle for 7-10 miles after a fill up will do this. leaving the vehicle running while filling up will do it, wacked out maf scaling can as well.
    The most hated, make the most power.
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  8. 09-14-2013 #8
    GPGTP
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    I think you mean 7-10 minutes right? Lol. Will a whacked out Maf do this?? It's an alcohol sensor, I thought it didn't care.
    Last edited by GPGTP; 09-14-2013 at 09:26 AM.
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  9. 09-15-2013 #9
    goofee
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    Acording to service information a 2013 sierra still uses a virtual sensor. A bad maf can throw it off. A co worker of mine added a cold air intake to his 2011 truck without any programing and it would get the wrong alcohol reading every time he filled up. Went back to the stock air box and never had a problem. I didn't have HPTuners at that time.
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  10. 09-16-2013 #10
    Area47
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    Quote Originally Posted by GPGTP View Post
    I think you mean 7-10 minutes right? Lol. Will a whacked out Maf do this?? It's an alcohol sensor, I thought it didn't care.
    No, I was accurate in the time it takes for the calculation to settle in. I watched numerous times on my 2010 6.2 silverado after i filled up. It would not kick in for about 5 mins, then the trims would change and the stoich value would follow suit. Again. I was no where near remotely joking about the time needed.

    If the maf scaling is way off it will throw the stoich value off as well. Then you run into the situation the OP has. It is not an alcohol sensor anymore.
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.
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  11. 09-17-2013 #11
    13Sierra6.2
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    Great info guys thanks again...I got my hands on a Tech2 found the fuel stuff and there is an Ethanol learn section, but the problem is i dont know the sequence to get it to re calibrate. Anyone on here ever did it? I guess im gonna have to start calling around and find someone to give up what they know so i can get this problem fixed.
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  12. 09-17-2013 #12
    Area47
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    there is a write up in S.I. for it if you have access to the gm system.
    The most hated, make the most power.
    93 Ranger. 5.3 D1X. 1069hp.
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