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Thread: Need Help/Input Lazy 02's

  1. #1
    Tuner in Training
    Join Date
    Apr 2018
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    Need Help/Input Lazy 02's

    Ok, I picked up a 2008 Chevy 1500 RCSB 5.3l Auto Flex about a month ago. I plugged in and found the ethanol content @24% and LT fuel trims approaching -20 on both banks which is way too high, I ran a few tanks of premium(91) through the truck and the content level did not change. To my knowledge Hptuners doesn't allow me to reset the Ethanol content so I used tech2 to reset to 3%. I then reset the LT trims and started logging. The fuel trims went right back to high negatives almost immediately. The 02 readings seem extremely sluggish to me and I'm hoping one of you fine folks can take a look at my log and give me some input.

    2008ChevyTrucklogafterEreset.hpl

  2. #2
    Advanced Tuner
    Join Date
    Sep 2018
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    213
    Did your ethanol percentage go back up? I've seen a lot of the flex sensors go bad and cause this exact issue. Disable flex, reset trims, and log to confirm.

  3. #3
    Tuner in Training
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    Apr 2018
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    This truck doesn't use a physical flex fuel sensor, it uses a virtual sensor.

  4. #4
    Tuner
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    Aug 2008
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    Chicago
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    I would disable the virtual sensor and run an actual sensor. You cant reset the ethanol content either. The only way to get it to relearn the ethanol content is after a refueling event and you have to drive it. I cant remember how long, but I think its 7 miles or maybe a little more. Try driving it for 30 minutes on the highway and see if it relearns after a re-fuel. I used to run into this a lot on the late 2000's Impalas with virtual flex. They would always have e10 but end up learning a higher ethanol content. The fix was an ecm reprogram, refuel and roadtest.
    2000 WS6 Trans Am LS3, Tick Performance Stage 2 cam, ARH 1 7/8" Headers, FLT Level 6 4L60e, Circle D 5c Launching on a 200K 10 Bolt

    2001 Camaro SS M6 Black on Black

  5. #5
    Tuner in Training
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    Apr 2018
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    I've tried disabling flex in hp tuners and setting default to 5%, but I still had high negative trims with it disabled. So that's why I went the Tech2 route and reset the ethanol content. I cleaned the MAF about 300 miles ago as I suspected the k&n had been over oiled and coated the MAF, but that made zero difference in the MAF hz before and after readings.

    I feel like the 02's are super slow to oscillate, but that could be because it's running rich. I know I could tune the vve/maf and bring the trims down a bit but I I think that would be just masking a problem.

    Truck has 103k on the clock and spark plugs were changed about 5,000 miles ago. I got rid of the K&N filter and put a standard paper filter in. I've disabled dod and traction control and I don't want to go any further until I know it's running correctly.

  6. #6
    Advanced Tuner
    Join Date
    Sep 2018
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    e settings.PNG

    For virtual set this table flat across and see if fuel trims improve.

  7. #7
    Tuner in Training
    Join Date
    Apr 2018
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    Ok, I had some free time this evening so I've made the values the same throughout the entire table and I've set flex to disable. I've taken 3 logs after clearing long terms. My long terms were very slow to rise and this time around seemed to have settled to below 10% so I believe that has fixed the issue. I'll be ordering an actual flex fuel sensor soon. Is a dealer software update needed to run the physical sensor given the known issue with the virtual? I've found a write up for the physical sensor installation on a E38 Ecu in a gto seems pretty easy. I think I'm about ready to start correcting the VVE and Maf Tables. Is there a preferred order Maf or VVE first?

    log after flex fuel disable.hpl
    log after flex fuel disable 2.hpl
    log after flex fuel disable 3.hpl