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air to fuel ratio

EFI Tuning Fundamentals

Discussion and questions related to the course EFI Tuning Fundamentals

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Guy's in the video AFR . I can't understand lambda in those short words . And in the calcuation where did the 12.5:1 came from . Is that a readind based on a dyno pull ?

Thanks in advanced

I'll try to explain better:

Lambda is a measurement that is always relative to the stoichiometric AFR of a particular fuel. For example on pump gas with a stoich value of 14.7:1, if we are running with a measured AFR of 14.7:1 then the lambda value would be 1.00 (14.7/14.7 = 1.00).

The way to convert from AFR units to lambda is: Lambda = Measured AFR / Stoichiomteric AFR

If for example the engine was running on pump gas with a measured AFR of 12.5:1, then lambda would be 12.5/14.7 = 0.85

If you want to convert the other way, simply multiply the lambda value by the stoichiometric AFR for the particular fuel. For example if we have a measured lambda value of 0.95 and the stoichiometric AFR is 14.7:1, the AFR would be: 0.95 * 14.7 = 13.97:1

I trust this makes things easier to understand.


I am using NTK wideband AFR sensor with HKS AFK I, Is there any configuration to convert the value reading of AFR to Lambda in the ECU "AEM, G4 or Haltech" ? or I need to buy special gauge to read in Lambda.

Thanks In advance

Both the Haltech and Link G4+ ECU have the ability to display air fuel ratio in units of Lambda or AFR. The older Link G4 will only display in units of AFR though.

With the G4+ you can change the display from the 'Options' drop down menu. Go to the 'Units' sub menu and select 'Options'. You can then configure how the units are displayed.

With the Haltech you can click on the 'Change Units' icon in the tool bar (the icon looks like a little set square) and then you can choose your units.