A/F mix at idle and just above

Engine, Trans & Driveline

  1. Moparfeind

    Moparfeind FBBO Gold Member FBBO Gold Member

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    Guys, my AF is like 22 at idle and just off idle and heads to 12 when I accelerate toward 2000 and above. This is measured at the tailpipe with my LM1 wideband O2 sensor. If this measurement is accurate does this sound reasonable? 12 might be a little fat but for now thats a good thing for me.
     
  2. moparedtn

    moparedtn Ed on the Ridge FBBO Gold Member

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    22??:eek::eek:
     
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    • 65-440

      65-440 Well-Known Member

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      22 ? Way lean ... 12 is ok under acceleration
       
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      • Don Frelier

        Don Frelier FBBO Gold Member FBBO Gold Member

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        I've never heard of measuring at the tailpipe. Should be a few inches past the manifold or collector. I don't think it will stay running at 22.
         
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        • Jcharger

          Jcharger Well-Known Member

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          Ditto. I have not had experience with an idle anywhere near an A/F of 22. I suspect there is something with the A/F measurement at idle. The other might be fine.

          Off idle can be lean though and that is a symptom that you can work on, but it also depends how long it stays that way and if it gives any problems. I am guessing it might be close to lean backfire if it holds for a long time.
           
        • Moparfeind

          Moparfeind FBBO Gold Member FBBO Gold Member

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          This is the wideband O2 sensor site.

          https://www.innovatemotorsports.com/products/db.php

          this is the tailpipe sensor

          so 22 is way out at idle...so looks like I need to fatten up the idle circuit on my Holley double pumper.

          33E98CF6-0FE3-436F-BEEE-AD899F215B13.jpeg

          not everyone has a bung hole to stick their O2sensor in ...... .... ... .. .
           
          Last edited: Jan 23, 2020
        • Kern Dog

          Kern Dog FBBO Gold Member FBBO Gold Member

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          My Charger idles in neutral about 13.5 to 14.0 when warm but fattens up in gear. My sensor is in the RH header collector. The gauge that I have has a narrow range, something like 10.0 to 18.0. It has idled off the charts lean, meaning something above the 18.0 limits and it was choppy and erratic.
          I've had mine set to run in what was considered to be optimal, 14.7. It didn't run as strong though. I do wonder if the "Up to 10% Ethanol" in our gas here skews the numbers at all. I run richer than the suggested normal numbers for power. I guess if I were to tune for economy, I have the wrong car anyway!
           
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          • Moparfeind

            Moparfeind FBBO Gold Member FBBO Gold Member

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            Thanks KD. So is your AF mix fairly flat from idle all the way out?
             
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            • Kern Dog

              Kern Dog FBBO Gold Member FBBO Gold Member

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              Oh, no....It jumps around a LOT.
              I've read that it is the transitions that pose the greatest difficulty for carburetors. Tuning for WOT or idle is relatively easy. Getting the numbers to move gradually may be an impossible goal. Mine runs great and has no bad manners but in Park or Neutral, if it is idling then I stab the throttle, it goes lean for a split second then down to 11.8 or so. Lifting the throttle before 5500 or so, it fattens up for a moment as if the engine is using up a stream of accelerator pump fuel, then it settles to the middle of the range. In gear, it will run in the mid 11 range at WOT. That is supposed to be richer than ideal but when I have jetted down to lean it out, the power dropped off.
              I have a Demon 850 vacuum secondary, very similar to a Holley. There may be some gains to be found in the primary metering block. I have a "Quick Fuel" metering block in mine with replaceable jets for the PVCR...I'll explain more after dinner.
               
            • andyf

              andyf Well-Known Member

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              It isn't 22 at idle, your measurement is wrong. There isn't a lot of exhaust flow at idle so what you are measuring is a mixture of exhaust gas and outside air. You need to install a bung in the head pipe for the O2 sensor and then you'll get accurate measurements.
               
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              • Billccm

                Billccm Well-Known Member

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                I think at idle you have some regression that makes the tailpipe method skewed.

                My mechanical engineer colleague made a O2 tailpipe sensor and I tried it on my road runner. The pipe for the sensor was over 1 foot long. It took 30 minutes of driving around to get stable readings.

                Best setting I could get at idle was 14. It still smells slightly rich, but I kept it there.

                At wide open I was 13, and I replaced the metering rod with a -4% lean. That was a great change as the throttle response improved tremendously, and the AFR changed to 13.9 to 14.1 depending on the stomp of the pedal.

                I stopped there and have been happy with the performance.
                 
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