Lambda

A normalized air-fuel ratio where 1.0 is stoichiometric regardless of fuel type.

Lambda expresses air-fuel ratio relative to stoichiometric, so lambda 1.0 is always perfect stoich, 0.85 is rich, and 1.10 is lean, no matter the fuel. It is AFR divided by that fuel's stoichiometric value (14.7 for gas, ~9.0 for E85). Lambda matters because it lets you target combustion the same way across pump gas, E85, or a blend, which is why most tuners and dyno operators prefer it once they run flex fuel. A target like lambda 0.85 at WOT translates to different AFR numbers on different fuels but the same combustion richness. In HP Tuners VCM Scanner you can display wideband data as lambda or AFR; pick lambda when working flex-fuel builds to avoid AFR confusion. Always verify lambda from the wideband, since commanded lambda in the calibration is only a request, not what the engine actually burned.