[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.

So your cruise AFR of 13.8-ish is by no means rich at all, not even close to being too rich. Quite frankly if the engine cruises fine there without drivability issues like surge, hesitation, I'd leave it be.

The idle AFR however, I agree with Tom, way too lean even for real gas. Personally I would be richening the idle circuit. To get that in a safe level your mixture screws may or may not be active enough and sometimes it's necessary to increase the idle feed restrictor size.

Keep in mind any increase in AFR on the idle circuit will also increase the overall AFR throughout, so your cruise and wide open throttle AFR's will fatten slightly. So you may or may not want to make other minor changes to get your cruise back where you want it.

[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.