Question about STFT

[pauly24]

Ive searched this forum and I know WHAT the STFT are, but I don't understand how they work.
Is it just the feedback between the O2s in CL mode and the commanded AFR. So it will inject the amount of fuel it thinks it needs for stoich, then the O2 lets the computer knows it was off and it can correct by X amount, which is the STFT.

If that is the case, then do fuel trims ONLY work in CL mode? If so why do you have to disable the STFT when you force the car to stay into OL mode?

[odd boy]

1. O2 will take you to stoich
2. WOT will not be stoich
3. O2 are narrow-band and not capable to read WOT numbers in some cases, this is why stand alone systems require wide-band.

[pauly24]

EDIT: ALL GOOD. worked it out...

few more questions.

1. numbers for BEN around 1 give or take 0.02 are good yes?

2. And are these BEN factors directly proportional to what you would see in the STFT logs?

3. Once you turn your STFTs on are your BEN values meaningless, because now you are comparing an AFR that has been corrected by the STFT against the commanded AFR, so if your logging BEN with STFT on then all the values should average out to 1?

[joecar]

1. BEN at 1.00 +/-0.02 is good.

2. No. BEN's would be closer to following LTFT's (see next post).

3. Correct, STFT is correcting actual AFR to stoich (i.e. same as commanded AFR), so BEN goes right to 1.00 (tightly cycling around 1.00 with very small amplitude swings).

[joecar]

When STFT's hit the threshold (positively or negatively), the PCM bumps LTFT's (up or down) and resets the STFT's.

[pauly24]

The BEN is form a run just after I dialed in my VE table.

Only the areas under 2200 RPM and 75kpa were done as you can see, but I think im on the right track.

The other picture are my STFT once I have enabled them in the tune, these STFT seem to be pretty large though.

I think i know why, when I dialed in my VE, I set my commanded AFR to 14.5, once I enabled my STFT, they had to kick in and bring it to 14.68 and hence why my STFT are off? is that right? Oh also I only changed my VE IMTV OPEN table, I should copy and past it onto my CLOSED table as well, so the changes I made haven't even affected my CL mode yet... right?