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Lambda VS AFR – Jay’s Tech Tips #35 – Real Street Performance

August 21, 2019

Hi, I’m Jay from Real Street Performance. Today we’re going to talk about how to use your wideband air/fuel ratio gauge and interpret the data that it’s telling you. For sake of discussion and trying to get you guys to understand this concept, we’re talking about stoich. Your target air/fuel ratios will often be different than stoich. A wideband O2 sensor has a 0 to 5 volt range, and it will output a signal from a 10 air/fuel ratio to a 19.0 air/fuel ratio and everything in between with pinpoint accuracy. A narrowband O2 sensor has a 0 to 1 volt output. And it will just read above or below stoich. So it’s used for factory systems to control closed-loop fueling under low load for good gas mileage, but it does not output a signal that you can identify as an air/fuel ratio. Since a narrowband sensor can output an actual air/fuel ratio, we just don’t use them for tuning. The exhaust gas leaving the engine is a mixture of air and fuel. If there’s too much air present the mixture is lean, and has too much fuel present the mixture is rich. If exactly enough air is provided to completely burn that amount of fuel, it’s called the stoichiometric ratio. Different fuels have different stoichiometric values. Some require more air than others to create a stoich mixture. For reference, pump gasoline has a stoich ratio of 14.7:1. So that’s 14.7 parts air to 1 part fuel to create a stoichiometric mixture. This is why most of the commercially available wideband O2 sensor gauges on the market are 14.7 when you click them on cuz that’s the stoich ratio for pump gas. This is why most of the aftermarket wide bands are set up with a 14.7 stoich ratio because they’re assuming that you’re running on pump gasoline. When you’re using your wideband air/fuel ratio gauge as a tuning tool, you have a target that you’re trying to reach. So you’re going to adjust your fuel map to reach that target. But we know that the air/fuel ratio is different for each fuel because the stoich ratio is different. Since different fuels have a different target air/fuel ratio for stoich, if you drain the gasoline out of your car and put ethanol or E85 in it, would you target a 9.7 air/fuel ratio on E85 on the same gauge that was 14.7 on gasoline? You would have been making a mistake if you had done this because the sensor itself just knows that stoich is stoich and the gauge is configured on a gasoline scale. So even though E85 has a stoich ratio of around 9.7, the display on the gauge would still be targeting or you would still be targeting a 14.7 ratio. Don’t worry if you’re getting confused. Everyone else is too. There’s a much easier way to do this and it’s just a work in Lambda. Lambda is the direct output of the sensor that the manufacturers translate to an air/fuel ratio on the gauge. Most wideband manufacturers offer an option to display in Lambda instead of air/fuel ratio. So you can just get used to working in Lambda. The beauty of working in Lambda is regardless of the fuel you’re using, the stoichiometric ratio is always the same. It’s always 1. So if you’re tuning for power under boost, you may target 0.75 to 0.77 Lambda, and that’s just the number that you’re looking for regardless of the fuel that’s in the tank. So in my opinion working Lambda is easier because you don’t have to memorize or have any thought of a conversion between the actual sensor and the display because you’re always just looking for the target Lambda value you’re after. After installing a wideband there are some people that overreact because they don’t know how to interpret what the wideband is telling them. It’s normal for the gauge to display lean during deceleration. The ECU generally cuts fuel while you’re slowing down because the engine doesn’t need fuel injected in it to slow down. During part bottle cruise, it’s normal to see ratios if you’re working the Lambda of 0.95 to 1.05 or air/fuel ratios of 14.0 to say 15.5. Totally normal. It’s normal to see on a naturally aspirated engine under high load or wide-open throttle a Lambda value of 0.85 to 0.91 which is going to be 12.5 to say 13.3 if you’re still working in an air/fuel ratio. If you have a forced inducted or a boosted engine, you’re generally going to see 0.75 to 0.80 in Lambda or 11.0 to 12.0 air/fuel ratio under high load. The sensor relies on an internal temperature for its calibration to be correct. That’s why it has a heater circuit. If you first start the car up, the display may not read correct until it reaches its operating temperature. If the sensor becomes fouled or damaged or just wears out, it’ll typically read lean under no load or loaded conditions where it’ll just go to the top of the range and just sit there. That’s when you know it’s time to buy another sensor. Hopefully this information helps you understand what your wideband gauge is trying to tell you. And you can see what’s ordinary and what’s out of the ordinary. If you have any questions, you can consult the guy that tuned your car or give us a call or post questions in the comments below. Thanks. and I’ll see you next week.


  • Reply frankycomeau September 30, 2015 at 9:58 pm

    love these videos! great way to learn more about tuning. keep it up Real street !

  • Reply Peirre Gale September 30, 2015 at 9:59 pm

    Every single video is on point.
    Extremely useful!
    Thanks for the uploads, I learn something new with every video.

  • Reply Jeffrey Sanchez September 30, 2015 at 10:08 pm

    Wow. Jay keep these videos going! There so Helpful!

  • Reply 170turbo September 30, 2015 at 10:51 pm

    Very useful. Nice one!

  • Reply eagle September 30, 2015 at 10:54 pm

    Finally learned when to replace my sensor, that's some useful stuff right there!! Keep it up with the videos !!

  • Reply Michael Casella October 1, 2015 at 2:53 am

    tech tips are my favorite videos out of all the channels I'm subscribed too

  • Reply chad tuggle October 1, 2015 at 3:28 am

    would changing sizes in intercooler piping change anything in the fuel ratios?

  • Reply Austin Roe October 1, 2015 at 6:47 am

    these videos are great keep them coming!

  • Reply Alberto Salcedo October 1, 2015 at 6:11 pm

    So would i need to buy a new gauge if its set for gas 14.7:1 & im running E85 which is 9.7:1???

  • Reply Rath3ON 420 October 1, 2015 at 7:12 pm

    This is Awesome Jay. i never knew what lambda was and AFR's was just tuners saying "keep it close to this". this makes wayy more sense. Thanks again these tech tips are the best on the net. very easy to understand and useful stuff

  • Reply Brandon Molzan October 1, 2015 at 11:30 pm

    I just installed a lc2 in my evo and its on e85. its was calibrated while on e85. it ranges from 10. to 15 depending on acceleration and decel. is that a correct reading?

  • Reply Santiago M October 2, 2015 at 11:01 pm

    If you want your ride to run like a beast all day & all nite then take it too Jay & the crew at Realstreet Performance! Holla:^)

  • Reply Review Guy October 4, 2015 at 11:01 pm

    My NGK AFX wideband goes from 9 to 16 on the af ratio. Does that mean if im at 14.7 on that gauge im running lean ?

    I know from the instructions i've read it recommends that 13 is around the stoich since the gauge maxes out at 16 that means 14.7 would be close to a full lean reading on that specific gauge. But maybe it still has no problem at 14.7. However i will say that my supra thats on a ecu masters stand alone does not like idling at 14.7 at all. It prefers the higher 13's for idle.

    So far though that is my main issue is getting idle perfect and trying to sort out the cold idle. It just doesn't wanna idle cold. But after i do get it warmed up it runs for me all day.

  • Reply Manny Jr October 9, 2015 at 5:24 am

    Have a question if my car was turned on q16 and i have retuned on 91 octane is it okay to mix little bit of q16 with the 91 also have a aem wideband o2 sensor

  • Reply Viperman1979 October 23, 2015 at 7:51 pm

    How is the sensor mounted in the exhausted? I installed it in the top of my exhaust because my old lambda sensor was in that same place. Just replaced it with a wideband sensor

  • Reply Abdulnasser S November 19, 2015 at 12:50 am

    Great information, that was something i want know from long time, Thanks RSP

  • Reply Hom Holm January 26, 2016 at 5:57 pm

    These videos are mindblowing! I learn so many things each video, keep posting!!!!! 🙂

  • Reply Hammerhaus Kennel February 2, 2016 at 5:06 pm

    You guys crank out a ton of good videos!

  • Reply chip patton February 18, 2016 at 1:56 am

    I am so glad you made this video big help in clearing up wide ban afr's

  • Reply Brandon Wilkerson February 19, 2016 at 1:00 am

    what wideband do you guys prefer, AEM, PLX, or the Innovate?

  • Reply Georgios Tsalamandris March 30, 2016 at 5:24 pm

    Great info man.

  • Reply graham19922011 April 13, 2016 at 8:27 am

    So I'm a little flustered on which direction to go since i haven't really made my mind up on e85 or pump gas. In realistic terms and regardless of whats easier, I'm assuming it would be best to consult my tuner on this? Also, if he says "i don't read lambda" then I'm basically stuck with pump gas since I don't wanna mess with "the gauge reads 14.7 so thats 9.7 in e85 stoich" and so on. Correct? Thanks for any feedback, have really enjoyed learning so much on your channel when its simplified!

  • Reply Dan Gunning May 26, 2016 at 9:06 pm

    awesome video, thank you

  • Reply c0V3Ro July 13, 2016 at 6:41 pm

    Wow! I was targeting 0.88 on E100, 10PSI.

  • Reply eurotouringautos August 4, 2016 at 3:30 am

    that was some great information

  • Reply projectzlowpoke August 8, 2016 at 6:16 pm

    one of the best compiled informational series on the internet. Thanks guys

  • Reply Don Rossco Joe October 13, 2016 at 9:09 am

    Narrow band sucks ass!!!

  • Reply john smith October 13, 2016 at 11:10 pm

    The best car channel. PERIOD

  • Reply Andre Buxey October 31, 2016 at 7:48 am

    Stoich.. Stoich.. Nioce!

  • Reply Aniruddha Mulgund December 18, 2016 at 7:04 pm

    I am using the wideband O2 sensor to tune a single cylinder NA motorcycle engine. The confusion I have is, the intake pressure will vary under loaded and no-load condition, so should I conduct these tests on a running motorcycle i.e. under load. IF yes then what is an ideal reading I am targeting across the rev range? Thanks!

  • Reply Simon Inga April 8, 2017 at 4:35 pm

    You said it should read lean on deaccelleration, mine is reading 22afr, which as lean as it goes, is that still normal? stock car, just added a wideband.

  • Reply The potato Party pooper April 12, 2017 at 4:22 am

    i have a few qs:
    1.will the AFR works on carbureted engine?
    2.if so,do i have to install more than 1 on weber 4 cylinder cause the tuning for each is different i pressume?

  • Reply ThatSubieGuy May 4, 2017 at 8:33 pm

    So is my sensor bad if the afr readings are jumping between 15 and 20 on idle or could it just be a grounding issue of some sort?

  • Reply Luis Jaramillo June 4, 2017 at 5:14 am

    omg love this now i understand my gauge but just have a question when im on idl car not moving fully warm my gauge reads 19.x some times would go to like 20.x it would just jump in between is rhis cuz of the factory setting the gauge comes with

  • Reply Donovan Drew June 12, 2017 at 11:24 pm

    REALSTREETPERFTV what is the song name you use for your intro?

  • Reply biplab biplab June 25, 2017 at 11:08 am

    petrol engine air fuel ratio?

  • Reply Justin Hoth July 6, 2017 at 5:30 pm

    starting to get into dsmlink this helps immensely thank you

  • Reply AOGDC10 August 16, 2017 at 1:48 pm

    Thanks for clearing that up!  If you plan on running e85 and you buy the AEM wideband gauge, they give you different gauge faces for gas/lambda.  They try to explain the theory of operation for different fuels, but it leaves you with more questions.  They don't explain that you'll see gasoline AFR if you are running e85 or why that is.  These are the explanations that are missing as we're learning to build/understand hot rods.  GREAT CHANNEL!!!

  • Reply Pryde Racing October 11, 2017 at 6:59 am

    Sir I have a question. Instead of making the switch to Lamda couldn't we just use the chart and adjust the Air/Fuel according to the applicable fuel we are using?

  • Reply Tomasz Wojcik October 16, 2017 at 1:42 pm

    Awesome video and nice to see no trolls disliking the vids

  • Reply Alex Blaska November 19, 2017 at 2:03 pm

    So if my car is flex fuel tuned and i switch between 93 and e85, its almost pointless to get a wideband because it wouldn’t be accurate for e85 and 93?

  • Reply January 15, 2018 at 3:11 pm

    best explanation!!!!! Thank you!

  • Reply sajad yaqub June 24, 2018 at 7:15 am

    You’re the real deal! Glad we you sharing these type of information

  • Reply issa STORM August 3, 2018 at 9:21 pm

    I buy it today 😋😋 but i donot know why make software i think its not watt software

  • Reply Ken Boost September 5, 2018 at 2:50 am

    Best explanation ever I have been looking for a long time to understand this
    you made it so simple to Understand 👍🏽

  • Reply Saad Hussain September 11, 2018 at 4:51 pm

    i have a jzx100 tourer v thats been running extremely rich, under high load i can smell the fumes from my exhaust and theres black smoke. Also my water temp gauge warning light is always on from the moment i start the engine. could it be a faulty water temp sensor thats forcing the engine to remain rich?

  • Reply Mike G September 15, 2018 at 10:53 pm

    Good video…

  • Reply Vincent McAllister October 8, 2018 at 6:43 pm

    Who at Real Street is the Jill Scott fan? lol. Yeah I caught that!

  • Reply Ase Morton December 16, 2018 at 7:16 pm

    Is there a Fail safe version of the AEM X Wide Band O2 Senor??

  • Reply Dave A March 1, 2019 at 11:08 pm

    very good video, and very good explanation!

  • Reply ForAl lMankind March 7, 2019 at 7:57 pm

    Straight on point, Hi there, i'm gonna try my question here, hope no answer though, but here i go :
    I recently put a new 0² sensor on my car, before doing that i was feeling my acceleration had some kind of stair like gradually getting in it while full throttle. my average mpg wasn't good but all in all wasn't that bad, considering the overall rating of this car. But now with the new sensor, my acceleration is shabby like restrained for some reasons, feel continuous though with no step or bump into it. But my mpg go down like 10 to 15% down : ±405 miles before and ±360 miles after. Is there any kind of run-in cycle or brakes in, that i missed, or something ? my local tech doesn't have any clue, and want to make a full diagnostic on my car.
    any thoughts about what's going on ?
    -Best regards.

  • Reply Matthew Moore March 21, 2019 at 11:27 pm

    Your work and intelligence is very much appreciated!

  • Reply Numinous April 15, 2019 at 4:18 am

    My factory wideband measures from 8.97 to 29.29. Thanks, Mazda, for giving me such awesome measurement from the factory on my Mazdaspeed 3 XD

  • Reply aamir najeeb May 17, 2019 at 11:37 am

    What should be the reading on afr with just ignition on does it should read full lean seems like my gauge still reading even though ignition on (left the ignition on for few seconds)

  • Reply Supra Drift May 27, 2019 at 8:27 pm

    I always like to use Lambda on my fueltech although I have the option to use afr, much easier to read . thanks Jay !

  • Reply VW Fixit June 26, 2019 at 9:17 am

    Thanks helped alot

  • Reply LMansley July 2, 2019 at 11:50 am

    thanks for this!

  • Reply Alex Brooks July 9, 2019 at 12:39 am

    Can you explain more about lambda

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