Changing Stoic and user math

[ivancolesnic]

Trying to tune for 14.1 AFR, changed my Stoichiometry to 14.12 and my equivalence ratio commanded displays as 14.12 in VCM scanner, but my math seems to be wrong, because at 14.2 on my wideband it shows as rich on my eq ratio. I have the formula provided by 100*[(formula provided by AEM - which just converts voltage to a AFR) - equivalence ratio commanded]/equivalence ratio commanded. Equivalence ratio commanded in this case is channel 50118.238. I suspect that this channel is not the same as my equivalence ratio commanded displayed in VCM scanner. What do I need to change? If I turn on my fuel trims it also seems to set AFR back to 14.67?I know there is a way to do this because I?ve seen people do it, I just don?t know how.

[gametech]

Narrowband fuel trims will always try to correct back to actual stoichiometric regardless of what number you put in or what fuel you use. They are uselessly inaccurate at any other A/F ratio. Or maybe I am misunderstanding your issue?

[SiriusC1024]

The scaling for Commanded AFR needs to match measured AFR.

Put stoichiometric at factory 14.68. Widebands operate on the same principle as narrowbands. The inflection point is the chemically stoichiometric ratio. The wideband will output the stoichiometric ratio as 14.7 no matter what. Another way to look at is make the stoichiometric ratio in the tune what the wideband considers as stoichiometric.

If you're wanting a different ratio then use Equivalence Ratio. Your confusion is thinking EQ is in AFR. It's in Lambda. 1 EQ = 1 lambda. Compare error between Commanded EQ and wideband Lambda.

[ivancolesnic]

Got it, so instead of changing stoichiometry to 14.1 got to change my lambda/eq to .96? So then 14.7x.96=14.112 and that will give me my desired AFR. And that?s under EQ ratio where my STFT is also?

[Alvin]

You should stop working with AFR. Switch to EQ ratio

All O2 sensors, narrrow band or wideband are looking for a stoich burn. They don't actually report back 14.1/1 etc.

A well tuned E85 car that runs at 9.86:1 will read 14.7:1 on a wideband calibrated for gas. Does that make sense?

[SiriusC1024]

No. You can keep your 14.1 for E10. Log commanded EQ and make the wideband report Lambda. Use the error for those two.

Using AFR you'd be 14.1 commanded and the wideband would read that as 14.7. The wideband has no idea in AFR mode and it just assumes pure gas.

Read up on Lambda vs AFR if you're having trouble understanding.

Btw the OL tables, including PE, are in Phi. Phi = 1/Lambda (inverse of Lambda). For example if PE is 1.2 that means your wideband will show 0.83 Lambda during power enrichment.

[ivancolesnic]

So it looks like I have my formula already set up for Lambda (not AFR) with my AEM wideband logging. Using the .1622*volts+.4990. So my lambda reading is at 1 for stoic regardless of what fuel I am using? So when I am logging my EQ ratio I am logging % rich or lean of lambda because of the formula I am using and lambda is 1 regardless of the fuel I am using? Does the wideband signal to the ECU use 1 as lambda and adjust from there like the AEM? What I am understanding you say is that instead of looking at my gauge in AFR I should be looking at it in lambda and not AFR, because it is automatically multiplying lambda by 14.7 for me and without me telling it that I am using E10 it won?t multiply by 14.1. Seems like the logs I have are correct and I was throwing myself off by looking at the AFR on the gauge.

[SiriusC1024]

Yep you got it now. Except the wideband signal to ECU part. The ECU doesn't receive wideband. Scanner can pick it up because that's how you have it configured. The wideband reports voltage, and the formula converts it.

[ivancolesnic]

What?s even the point of using AFR then? Shouldn?t it all be in Lambda? I tune it to run lambda 1, it doesn?t care if I use e10 or e30, lambda is still 1, so I am just adjusting fueling to whatever is in my tank, be it e10 or e30.

[Alvin]

What?s even the point of using AFR then? Shouldn?t it all be in Lambda? I tune it to run lambda 1, it doesn?t care if I use e10 or e30, lambda is still 1, so I am just adjusting fueling to whatever is in my tank, be it e10 or e30.

That's right.. That's why most experienced tuners don't mess much with AFR.

It could be on Propane and if lambda = 1 than it is stoich.