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Decel AFR

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  • Decel AFR

    I have an AEM wide-band hooked up and have been monitoring and tuning. One thing I noticed that contradicts what I though should happen is that when say I'm heaving on the throttle and let off and decelerate the AFR is very rich (9-11). I would expect the opposite in this situation. I am looking at the acel/decel maps to understand better what it's doing. Thought?

  • #2
    If you just gave it "gas", then cut off the "air". It will always show "rich" till the gas burns off.

    I just look at the duty cycle of the injectors for deceleration...should go to 0 when throttle is closed, then burns off the suspended fuel, then goes too it's idle ( in gear ) duty cycle.
    At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy


    • #3
      Sounds like you're not getting into decel fuel cut. If you're very rich in decel it's because you have too large an injector pulse width value in the low load, high rpm section of your fuel map. But really, the fuel map values in the decel area shouldn't really matter because the injectors would normally just be cut for decel. Unfortunately I've never used Pro-Flo 2 before so I can readily give any suggestions on where to look to check DFCO status.

      Not all EFI systems will report 0% injector duty when in DFCO because a lot of times the duty value is based on the current live cell values from the fuel map which you're always in even if the injectors are off. It's been my experience that AFRs will report dead lean almost instantly after DFCO becomes active as any residual fuel is usually consumed within an engine cycle or two which doesn't take very long at high rpm.

      Accel/decel maps typically account for rapid opening or closing of the throttle. You normally increase fueling over base when opening the throttle and then reduce fueling over base when closing the throttle from a more open position but not going completely closed. I'd just focus on making sure you're meeting the DFCO requirements because it sounds like you're not.


      • #4
        This is from the manual: "During any closed-throttle decelerations that begin with the engine speed
        above about 2300 rpm, the fuel is cut completely off and remains off until the speed drops to about 1800 rpm."

        Here is the only map I see that is related


        • #5
          Right, that's how decel fuel cut is supposed to work - IF you meet the trigger criteria which you're most likely not otherwise you'd go into fuel cut. That table doesn't have anything to do with decel fuel cut besides having the word decel in its name. That's an acceleration enrichment table. Not referenced in any way for deceleration fueling.

          If you want to "fake" decel fuel cut, just set the fuel map cells in the high rpm decel area to zero. If that works (which it will), then it proves that A) your fueling is being determined by the main fuel map only and B) that you're not going into actual decel fuel cut. There are sometimes max throttle position thresholds as well as manifold pressure thresholds to activate fuel cut. For instance, if decel fuel cut throttle trigger is 1% and your resting throttle position is 1.5%, decel fuel cut won't turn on. You need to check your decel fuel cut trigger settings.


          • #6
            Anyone else know about this setting for ProFlo2? I really can't find much of anything about this. Really does seem like the cutoff doesn't occur for me.


            • #7
              Actually I am having the same thing and could not find where in the B-editor to look for.
              496 in a 454SS truck, Pro-flo 2 and "remote 80MM turbo"