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How to read STFT as a percentage - as it says unitless


benjigreen
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 I have a question I can’t find anywhere in the data logger I’m trying to read STFT as a percentage but it just says unit less and I can’t seam to work it out it’s saying 0.85 I’m just wanting to know the percentage of fuel it’s adding as I’m having o2 issues and trying to work out why but finding the logger a bit difficult to work out hopefully This makes sense.

and if anyone has any saved logger files they might want to send through to help that you may have custom made that works well? Hopefully this all makes sense. 

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Here is the background information on STFT and LTFT in the logger:

STFT will be the commanded lambda that the vehicle is commanding. Unless under open loop fuel control the vehicle will be bouncing this around from lean to rich to cycle the catalytic converter enable it to operate correctly. 

LTFT is a better measure of how well the fuel system is working. As the LTFT tends to 1.0 it means the area where this is happening (RPM and Load) has good data (Injector data, speed density, ...).  Below 1.0 it is richening the mixture and above 1.0 it is leaning the mixture.

LTFT will be useful when the vehicle is in closed loop fuel control and is a good measure of the tune configuration. Don't get too tied up with getting the values below 2% as that is where you will struggle to get below unless you have a perfectly matched set of injectors (most are within 5% of their rated and actual flow).

Now the % question might be covered with an upcoming release of the logger which has Histograms (and other really cool features). I will raise a support ticket to investigate further.

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We will add lambda units (percentage %) to LTFT for next release. Histograms will allow you to apply values as a percentage of the existing map. I can't give a release date due to the large of amount of updates going into it, but can say that the histogram work is ready for internal testing

 

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  • 5 months later...
On 2/21/2021 at 11:15 AM, Darryl@pcmtec said:

LTFT is a better measure of how well the fuel system is working. As the LTFT tends to 1.0 it means the area where this is happening (RPM and Load) has good data (Injector data, speed density, ...).  Below 1.0 it is richening the mixture and above 1.0 it is leaning the mixture.

is this right or is it the other way around? in the injector scaling forum when your histogram showed below 1.00 values you said you needed to take out fuel as the slow slope was far too rich?

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  • 1 month later...
On 7/23/2021 at 2:20 PM, john.z said:

is this right or is it the other way around? in the injector scaling forum when your histogram showed below 1.00 values you said you needed to take out fuel as the slow slope was far too rich?

I added about 22 percent fuel to the entire range using the speed density table.

At idle and cruse the LTFT was saying 1.21...at full throttle it was saying 0.75.

i think i have a fuel slosh/pickup issue anyway..

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