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Thread: Commanded AFR has changed on it's own

  1. #1
    Tuner
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    Oct 2012
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    Waterford, MI
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    Commanded AFR has changed on it's own

    My commanded AFR has always been 14.7, and 29.4 during DFCO (or FCO coast down). Suddenly it's not 13.79 and 27.58 respectively. My car is running horribly rich. Even during cold start, it's commanding the 13.79. It either commands a 13.79 or a 27.58. O2 wideband sensor? o2 downstream? MAF? MAPs? Any ideas? LNF 2.0L turbo, tuned, CAI, Manual....Any help is appreciated!
    Last edited by The_Ghost; 08-23-2019 at 11:26 AM.

  2. #2
    Tuning Addict 5FDP's Avatar
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    May 2012
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    Rogers, MN
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    Is it a flex fuel computer?
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
    Tuner
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    Oct 2012
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    No. Temp is also working fine. Fan comes on at 198 like it was set for...so I know it's not that. I'm leaning toward a bad (1 of the 2) O2 sensors, but not certain which one... Or the ECM has decided to take a %$#@.

  4. #4
    Potential Tuner
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    Apr 2019
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    Commanded doesnt just change on its own..... your car probably has a virtual E Sensor for flex fuel and detected a difference in Octane.... whenever this happens it goes off your Stoich AFR and changes according to the content of alcohol.

  5. #5
    Tuner
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    Oct 2012
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    Considering its an '08 LNF Solstice, I don't think so.... My question though is something new I've found. I've had it dyno tuned... And I just replaced the exahuast from the cat to the y split. And this issue started right around that time. I found some old data logs where my downstream O2 sensor wasn't showing any data... Now it is. I'm thinking the PO and when my car was dyno tuned, the downstream O2 sensor was not plugged in. When I had the new exhaust put on, they plugged in my O2 sensor....would the downstream (even though I have an upstream wideband) O2 sensor suddenly working cause my car to run a richer commanded afr???? You guys are my last hope here. Most of the Sol/Sky guys have no clue what I'm talking about!!

  6. #6
    Senior Tuner cobaltssoverbooster's Avatar
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    Dec 2008
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    Nevada
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    4,179
    never tested that theory out but if cat OT is enabled it may trigger a protection event.
    rdrfabrication@gmail.com
    2016 GMC 3500 Denali Diesel
    2000 Ford Mustang - Top Sportsman

    Ecotec help can be found here:
    LNF-http://www.hptuners.com/forum/showth...357-LNF-Guides
    LSJ-http://www.hptuners.com/forum/showth...965-LSJ-Guides