Effects of Changing fuel with different stoich value

[Terminal_Crazy]

I've recently found out that the premium fuel has a lower stoich value than regular. 14.4 vs 14.7

How does this affect the tune?
Is this affecting my emissions test?

Thanks
Mitch

[steveo]

I've recently found out that the premium fuel has a lower stoich value than regular. 14.4 vs 14.7

citation needed

but at the same time if you have differently burning fuels, in closed loop it'll account for the difference (o2 sensors don't know what stoich is, they always aim for stoich)

[lionelhutz]

You have to differentiate beween stoichiometric and the AFR. Stoichiometric is the perfect fuel mix. AFR is the ratio where this happens.

The O2 sensors tell the PCM when the AFR crosses stoichiometric. So, they don't really care or know what the AFR is.

The ideal AFR of all fuels vary slightly. I doubt you would find any that are 14.7:1. The typical fuel with 10% ethanol is closer to 14:1.

That small change should not affect the emissions testing.