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# Choosing the correct afr

### Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

What is the afr at 1.0lamda please?

I'm responding here mostly to verify my own understanding of this.

Lambda 1.0 is a representation of stoichiometric afr. That is the ratio at which the oxygen in the air is perfectly matched to the fuel to

Completely burn all of the fuel/air mixture. It is therefore dependent on the specific fuel in question.

Assuming pump gas. Stoichiometric mixture = 14.7:1 = lambda 1.0

Jguysr you're bang on.

Nick, as Jguysr said it is fuel specific. Here are some common fuel AFR/Lambda Stoichiometeric ratios

Pump gas 14.7:1 = lambda 1

Ethanol 9:1 = lambda 1

E85 9.75:1= lambda 1

Methanol 6.42:1 = lambda 1

Diesel 14.6:1= lambda 1

This does also depending on how you're reading lambda 1. Most wideband controllers will not know what fuel you're running on and will assume its pump gas so lambda 1 will always relate to 14.7:1 . For example if you had e85 and had it at lambda 1 the wideband would say 14:7/1:00 but the engine would actually be 9.75:1. Hope that doesn't confuse you :)

As Chris has in his post, different fuels have different stoichiometeric AFR values, however the Lambda stoichiometeric value will stay at 1, this is why I prefer to operate in Lambda rather than AFR, as it is a fairly fuel agnostic value, and can't be misleading if the sensor is incorrectly configured.

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