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lambda and air sales

Understanding AFR

Discussion and questions related to the course Understand AFR

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does lambda scale and AFR scale can be use with the same probe ?

and if it's the same probe, does we calibrating the AFR each time we change the fuel ?


Edit: how to modifie the title of the post, because my French corrector write this title in place of " lambda and AFR scales "


i've just look the next course, and it is explain.

as i understand, sensor always measuring lambda (what i Think logic, because it only see the oxygen in the exaust ) and it can convert to AFR if we teach it the stoichiometric AFR .

Am I right ?

Bonjour Kevin!

To put it in simple words, all probes (or sensors) will measure in Lambda, regardless of the fuel type (gasoline, E85, etc...) Your controller or gauge will then do a mathematical equation to convert it in AFR depending to the fuel type.

So here's an example why lambda is easier to work with :

You have a car that runs Lambda 1.00 with gasoline. 1.00 is the Stoich ratio of ANY fuel, in the lambda scale. So if your controller is setup to show AFR scale of gasoline, you will read 14.7 on the gauge. This would be correct. However, if your controller is setup to show the AFR scale of E85, you will read 9.6 on the gauge, even thought you are running gasoline! It's the same for the opposite (running E85 on Gasoline scale will give you a reading of 14.7) So yes, in the AFR scale, you need to change the parameter of the fuel you are running in your controller to display the correct scale.

But in the Lambda world, 1.00 is stoich, anything lower than 1 is rich, anything higher is lean, regardless of the fuel you are running! You don't have to switch for different fuel.

Hope it helps,


Hi Frank !

thanks for your answer, it's was i guess, but now is more clear for me.


I found this a few days ago for another chap having problems understanding it - reference the different fuels' AFRs to the lambda. Don't worry about the mis-spelt word, it is in the link.