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EFI Tuning Fundamentals

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To help clarify Lambda no matter what fuel system will equal 1 for stoich power?

Gasoline: 14.7 = 1 Lambda

Methanol: 6.4 = 1 Lambda

Same for the rest = 1 Lambda?

If that is correct what is the Lambda for Gasoline 11.5?


Justin Takeuchi

The lambda value for Petrol at 1.1.5 AFR is less than 0.8 Lambda (probably 0.78 or something close).


Thank you Ludo86!

To calculate AFR from lambda, multiply the lambda value by the stoichiometric AFR for the fuel. ie 0.80 lambda on petrol is 0.80 x 14.7 = 11.76

To calculate lambda from AFR, divide the measured AFR by the stoichiometric AFR for the fuel. ir 12.5:1 on petrol is 12.5 / 14.7 = 0.85

So when setting up your tuning software to show Lambda, does it automatically detect the fuel type and adjust to suit....or do u enter a target AFR for it to reference from?

i.e running gasoline - 14.7 stoich, then change tune to say suit E85 - 9.8 stoich, the AFR is going to be considerably different. therefore the Lambda reading will need to be recalculated?

@51RAZ it's actually completely the opposite. A wideband controller naturally works in units of lambda. If you want to display in units of AFR the ECU will take the lambda value and multiply it by the stoichiometric AFR value entered into the ECU for the fuel you are using.

Oh ok, great. Thanks for that Andre..... to me it seems to be the better way to go then using AFR, less chance of error.

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