[amcmike]

Originally Posted by Formulajones

First you have to keep in mind, stoich with todays 10% ethanol fuel is not 14.7:1. It's 14:1. .7 richer than real gas. Trying to run the real gas stoich number with 10% ethanol fuel is beyond it's efficiency range.

While your correct about the differences between stoich values of different types of fuels, you have to be careful when applying it to a gauge readout. The O2 sensor is actually reading the ratio of excess air value above stoich, known as lambda. Then the gauge converts it to an "air/fuel ratio." Which means you have to know what the gauge manufacturer chose as the "stoich value" of the fuel. In most cases this is 14.7:1 (which as you said is for ethanol free).


So in reality, @ cruise the sensor was probably reading .94 lambda, and therefore the gauge was programmed to calculate to a 14.7-based afr. Unless of course, the OP was already reading in lambda and then manually re-calculating himself.



This is why I prefer using gauges that read out in lambda, as it takes that question out of the equation.