What should the commanded AFR be with 94 octane pump gas with 5% ethanol

Hello,

100% stock 2005 Cadillac CTS-V 5.7L LS6 daily driver.

I am curious to know if I should be adjusting my 14.7 : 1 commanded AFR to something around 14.3 :1 when running 94 octane pump gas with 5% ethanol?

Please provide comments and feedback.

Thanks,

Under what conditions? I would say 14.7 is still ideal for most in non-Power Enrichment cases.

Hi,

Under all driving / performance conditions i would say.

The theory being that the 5% of ethanol in the 94 octane pump gas changes Stoich from 14.7 to roughly 14.3 so I am just not sure if it makes sense to change the commanded AFR to 14.3 or just leave it at 14.7.

I was wondering what the norm was

David

You might be over thinking it. Normally, for emissions purposes, the ECU is set up for an AFR of 14.7, which is stoich' for petrol/gasoline.

The ECU doesn't "work" with AFR, but interprets the lambda sender value as AFR. When you change the fuel blend, the ECU is still going to target the stoich' of 1.0, and that will show/be read as 14.7:1, regardless of what it actually is.

Lambda for different fuel blends -

https://www.speednik.com/wp-content/blogs.dir/1/files/2018/03/big-fuel-test-part-5-e85-versus-winner-crowned-2018-03-15_15-35-22_700571.jpg

100% gas', E5, E50, E85 - assuming a modern flex-fuel capability, the ACTUAL AFR will alter, as seen in the chart above, as the ECU corrects the fuelling to lambda 1.0, and it will still appear as 14.7:1 because that's lambda 1.0 for gasoline.

NOTE, SOME ECUs may be 'smart' enough to identify the fuel blend, and change the reported AFR on the fly - but I'm not aware of any.

ok, fair enough. I believe I understand what you are saying and please correct me if I am wrong............

Basically the ECU receives data from the wideband O2 sensors and works in lambda always targeting a Stoich of 1.0 regardless of the fuel blend be it E5, E85 or 100% gasoline. AFR is simply a translation from Lambda with lambda 1.0 always being an AFR of 14.7 : 1

So my question now is..................

What is the "Stoich AFR" table used for in the HP Tuners VCM editor software (see attached picture)?

If I understand the question correctly, that refers to the target*, or actual, AFR which is converted to, or from, the corresponding lambda number, which is what the ECU actually uses.

*Can't recall which.

ok, so do you know why anybody would alter that table from 14.7 to some other AFR ratio?

I am trying to understand what that table is used for.

As far as I know its a vestige of GMs older flex fuel sensing via sensor vs their current 'virtual' flex fuel sensing.