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What is your Engine's happy idle AFR?

Discussion in 'Tuning À la carte' started by 04OWwhipple, Jul 5, 2019.

  1. 04OWwhipple

    04OWwhipple Member Established Member

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    I was just curious on what idle AFR everyone's different setups are running at and are happily idling smoothly at? Dialing in my Haltech Elite and my engine seems to be happiest at around 13.5-13.6 AFR. If i lean it out a little and target 14.0-14.2 I start to have little misfires and pops through the exhaust which lead to a slightly unstable idle.

    Setup is in sig but it is basically stock long block aside from going to 9.2-9.3:1 compression over the stock 8.5. Still on stock cams with unported heads
     
  2. 01blckcobra

    01blckcobra Active Member Established Member

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    Usually .98/1. 0r 14.6...
    I'd say you have problem mechanically or tune issue.
     
  3. decipha

    decipha EFI Dyno Tuning Established Member

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    its common for most engines to respond to slightly richer mixes at idle but in no way shape or form should it ever misfire near stoich. Most engines can tolerate 1.25 lambda or 18:1 gas AFR before misfiring at idle. This excludes older inefficient larger engines that are very inefficient and usually want around 12.5:1 gas AFR at idle and usually misfire over 14:1 gas afr.
     
  4. 04OWwhipple

    04OWwhipple Member Established Member

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    Thanks for the insight, I am new to tuning and this is my first car that I am truly venturing into. From what I have understood is that it is not abnormal for engine to like to idle anywhere from 13.5-14.7 but typically more on the rich end of things. I will take a video the next few days and post them on the symptom I am experiencing with leaning the idle out closer to 14.0 just to see what you guys think here.

    I work in Service for a Ford dealer and I just took a quick look at an 18 mustang 5.0 and it seems that the factory Ford tune has that car idling at 13.8-14.1.
     
  5. decipha

    decipha EFI Dyno Tuning Established Member

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    all production vehicles idle at stoich its required for US federal emissions

    since its obvious you are confued on AFR you should use lambda as its significantly easier to understand

    stoich = 1.000 (what the 18 gt u seen was idling at roughly 14.0 AFR)

    where as 14.0 AFR on your vehicle as you see it on your wideband is actually 0.95 lambda still 5% richer than stoich
     
  6. decipha

    decipha EFI Dyno Tuning Established Member

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    btw, the 18 gt is naturally aspirated and direct injected so its AFRs at wot and under load are not going to be applicable to your setup.
     
  7. 04OWwhipple

    04OWwhipple Member Established Member

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    Maybe I will look into starting to use and understand lambda over AFR. Now you said all factory vehicles idle at stoich which is 1.0 but then referenced the 18 GT I was comparing idle to and say that is normal to idle at 14.0 bit wouldn't this be slightly rich on the lambda scale?? Closer to 0.94-0.96?? Or did I misread what you meant there.

    I'm know that is a different setup and my WOT and loads will be different. I was just looking at the idle on that one.

    Sent from my Pixel 2 using Tapatalk
     
  8. 04OWwhipple

    04OWwhipple Member Established Member

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    Here is a quick idle video of my car at 14.5 at idle. If you listen closely you will here the "popping/misfiring" I am talking about. Right at the 15 second mark you will hear 2-3 light popping abnormalities out of the exhaust. They are subtle but that would help you gone in on it. If I richen it up at idle that gets better and pretty much goes away completely.

    Plugs are 2 heat ranges colder gapped at .025.




    Sent from my Pixel 2 using Tapatalk
     
  9. decipha

    decipha EFI Dyno Tuning Established Member

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    the 18 gt has a stoich reference of 14.08 AFR so 14/14==1

    where as your wideband default is set for 14.7 stoich AFR thus if you put it on the 18 GT it would read 14.7 when the car shows 14 on the gauge cluster

    this is why its best to uae lambda since it doesnt matter what stoich afr is it will always be 1.00

    I cant hear it on my phone sounds the same to me
     
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  10. 04OWwhipple

    04OWwhipple Member Established Member

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    Ahhh, yes no I follow. I was unaware that they used 14.08 as stoich instead of 14.7 but that makes sense now.


    I can hear it in the video but it is a really light sound. Maybe I'll try to get a better video up sooner. One that is more clear. And in the mean time try to see if I can isolate it to a specific cyljnder.

    Sent from my Pixel 2 using Tapatalk
     
  11. slo984now

    slo984now AKA 01yellerCobra Established Member

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    Every Cobra I've heard with an aftermarket MAF pops a little at idle. Your idle doesn't sound bad to me. You're running a tight plug gap and plugs that are colder than stock. You're not going to get 100% stock idle.
     

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