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Thread: Strange happening with Flex Fuel

  1. #1
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    Strange happening with Flex Fuel

    A quick background.
    2014 ZL1 E67 BTR3 cam, pullies, about 16 psi boost on stock heads, return fuel system.

    So I had the car tuned pretty good in OL running on E80. It would be close to 1.00 lambda cruising in OL whether in MAF only or SD. Then I ran out of E85 in my drums, so I filled up with 93. I reset the fuel trims at the gas station and cruised for about 20 minutes to let it all stabilize. Using the Special Functions in the scanner I forced OL and it was way rich.

    Attached is a scan of me cruising in CL, then about half way forcing OL for a bit, then back to CL.

    My question is why isn't the Flex sensor adjusting the tune? I would expect a few percent difference, but 15% rich is crazy.

    Attached also is the tune I'm running. Don't beat me up too much, it's a street tune. I'm concerned with why the sensor isn't adjusting under cruise conditions.

    I see in the log that it recognised I went from E79 to E37 after the fill up. Not sure why the PID above is still at E78 or even if that PID is relevant.
    I also see that the AFR is still reading 10.1895, this is strange since the PID saw the reduction in E. I suspect this is the culptri, but why?


    Can you guys give me ideas to check on this thing? Thanks for the replies in advance. - Mark

    HP Tuners upload RICH OL.hpt
    RICH OL.hpl
    Last edited by marksrig; 05-21-2022 at 12:38 PM.

  2. #2
    Advanced Tuner dhoagland's Avatar
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    Have you verified your sensor against actual ethanol content?
    I had a sensor that was consistently 10% off against actual content. I went through and adjusted the scale and got it reading accurately, but I wasn't happy with that.
    So I changed the sensor and this one is nuts on in mid range, about three% off at E-0 about 2% off at E80 (E80 is the best I have been able to get out of the pump)
    2011 Camaro 2SS Convertible L99 Bone Stock for now
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    Yea, My sensor is off by 6% on the E85 end and 0% at E10. The fuel is actually E85 according to the test and only shows 79%. I dont think the calibration error is the main issue though.
    The log is showing AFR of 10.1895. I decided to reflash the ECM and now it is showing the stoich for the 37.5% alcohol. Both PIDs are now at the same 37% after reflashing. Strange.
    Running after the flash the car was much better.
    I shouldn't have to reflash the ECM to get it to correct the AFR for the new percentage.
    Last edited by marksrig; 05-21-2022 at 02:36 PM.

  4. #4
    Advanced Tuner dhoagland's Avatar
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    Strange
    It will be interesting to see what it does when you refill with E85 (or go E Zero)…
    Keep us posted
    2011 Camaro 2SS Convertible L99 Bone Stock for now
    2003 Dodge 2500 5.9 Cummins QC 4x4. Airaid, 2nd Gen Intake, Grid Heater Delete, D-Tech 62/65/12, Magnaflow. Bully Dog: Propane Injection, Triple Dog W/Outlook Crazy Larry. Edge EZ, BD Flow-Max, 48RE: Sonnax Sure Cure/Transgo combination, Derale turbulator, billet input, Triple Disc, Super servo, 4 ring Accumulator. :beer

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    After I flashed it, I went to get some E0. the % went from E37 to E28 but again, only on the bottom PID, top still said E37. The AFR was unaffected by adding the E0 so that means the ECM isn't recognising the change. My FPCM is still powered up so I can get the fuel pressure from the stock sensor. Not sure if the FPCM has anything to do with the Flex composition or not.
    Last edited by marksrig; 05-21-2022 at 04:47 PM.

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    I'm beginning to wonder if this may be a canbus communication issue with the FPCM. The PID that didn't change is from that module. Possibly it isn't communicating back with the ECM.

    UPDATE: well I thought maybe the TAN and TAN/BLK pairs may have been swapped but switching them around did nothing to alcohol%. My guess is the canbus is in parallel so it communicates either way. I'm not to familiar with it. Every combination yielded the same results. Fuel pressure gauge worked every time, and the Alcohol% didn't. Now I'm at a loss of ideas.
    Last edited by marksrig; 05-21-2022 at 08:03 PM.

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    Another thought I had that may do this is under FUEL>FLEX FUEL> INFERENCE & BLENDING. I know that this is where a certain amount of fuel has to flow before the ECM allows timing and fueling changes.

    I've put the DELAY VOLUME at 0.00L and the TRANSITION VOLUME at 0.00L as well as trying a .01 in those places. Nothing seemed to help. If there was a value, the ECM wouldn't get any input because my old fuel pump is now a return mechanical system, this is why I put it to 0.00L

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    SOLVED:

    I was writing ^^^this, I realized under INFERENCE that my Comp Change Thresh was at 1.00. I was looking for the minute change from just starting and seeing the alcohol content jump around from 28.2 to 27.9 and back. It wasn't enough to trigger the other PIDs to register a change because the Thresh was 1.00.
    I changed the Comp Change Thresh to .0001 and flashed it in. There was finally a change and it followed the sensor this time.
    Last edited by marksrig; 05-21-2022 at 09:14 PM.

  9. #9
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    your ''comp change thresh'' is 100% that means it wont adjust until it changes a difference of 100% set that to 2% where factory has it should get it working

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    yours must not be set to percentage, that is the percentage change in ethanol it will adjust for, changing it to % will work best so your .0001 will be 1%

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    I see it says 1.00 and ya, there's no description at all, I assumed %. I changed it to .001 just to see and can see a change now just in the fluctuations of the sensor, but I've also did a wire swap and told the ECM that the FUEL SYS>General that the FPCM was fitted and the pump FIXED. I'm not sure which of these fixed it, but I'll try to determine it and report back.
    It doesn't make sense that it would just be Comp Thresh because the first log I posted at the top showed from E85 to E37 with no change.
    Last edited by marksrig; 05-21-2022 at 09:07 PM.

  12. #12
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    yes the sensor will always change to suit actual but the comp change thresh is the threshold it waits to adjust past to then adjust the fuel, so set at 100% for it to change it wont ever change as u can only go from 0-85% ethanol not over 100% ethanol difference for it to then adjust, factory is set to 2 percent so it dosnt move around with the small shifts all the time but anything over 2% it changes for

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    So you're saying 1.00 is 100%?
    Stock for this engine is 0.00 according to the repository 2014 ZL1.

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    I looked at a flex Silverado and it's thresh is 0.020 so Yea, I think you're correct 07GTS. Thank You!! Thank You!!


    I have a buddy and his tune is set to 0.000 but has delay triggers.
    What a confusing mess.

    I'll put the canbus wires back the way they were then.

  15. #15
    Advanced Tuner dhoagland's Avatar
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    Good info here!!!!
    2011 Camaro 2SS Convertible L99 Bone Stock for now
    2003 Dodge 2500 5.9 Cummins QC 4x4. Airaid, 2nd Gen Intake, Grid Heater Delete, D-Tech 62/65/12, Magnaflow. Bully Dog: Propane Injection, Triple Dog W/Outlook Crazy Larry. Edge EZ, BD Flow-Max, 48RE: Sonnax Sure Cure/Transgo combination, Derale turbulator, billet input, Triple Disc, Super servo, 4 ring Accumulator. :beer

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    Thank you 07GTS and all who replied.
    I put the canbus pairs back to the original pins and FPCM FITTED back to NO and all is still good. The alcohol comps are working as they should. I have no idea why I had 1.00 in the Comp Thresh cell. I guess without looking at a factory Flex vehicle, I assumed it meant 1%. A label might have helped.

    Attached is the log of the fix. You will see the PIDS for ethanol and alcohol follow each other as the sensor fluctuates at idle. I can now set that value at factory 0.020 like 07GTS suggested.

    Cheers,
    Mark
    Attached Files Attached Files

  17. #17
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    no worries, if u click on the symbol next to the value it will cycle thru its ranges so u should be able to select % instead (may be blank now) but if u see where the values above have the % symbol just click on the same spot on the comp thresh and it will then show a % symbol and show percentage figure

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    Oh crap.
    Yea, it was blank, but I just hovered over it and BAM! there they are just as you said. I selected %. Strange, I checked my other tunes and they all had 0.00 in the Comp Thresh.
    I still don't know how it got changed.
    I swear, I learn something new everytime I tune this car.

  19. #19
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    Well, I took the car out for a spin and although the Comp Thresh needed fixed, it didn't solve my rich issue. I'll have to post a log tomorrow, but forcing OL still showed my Lambda wideband going to .89 when it was around 1.00 on the E85. I guess I'll try replacing the sensor before messing with the STOICH table. I would've thought these sensors and the ECM could adjust my fueling better. Something is off.

  20. #20
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    unless there is some error in the injector data that will throw it out when ethanol changes, u mentioned a return fuel system but is there a mechanical fuel reg referenced to manifold boost/vacuum ? or is it a constant fuel pressure just returning to tank