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STFT and AFR error

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hi all, if you have your afr error down to a good number should the STFT also read the same? my afr shows 14.7 but STFT still show up to -15 while cruising at a staedy pace. does this indicate that the wideband in incorrect?

when you say it's at 14.7, is it an unrealistic 14.7, like it never moves or fluctuates at all? That could indicate something is up with the wideband. It's going to oscillate a bit in low load/closed loop conditions, and it's going to shift when you tip out (deceleration fuel cut) or tip in (during acceleration).

If your short term fuel trim is -15%, what is your long term fuel trim? It depends on the engine, but you may need to adjust your MAF sensor scaling, VE tables, or injector settings (some injector size constant, deadtime calculation, injector slope, whatever).

The AFR error and the fuel trims work hand in hand so you need to understand their interaction. The job of the fuel trims (STFT and LTFT) is to drive the actual AFR towards target. So if you're in a situation where the AFR error is zero and you have a negative fuel trim of 15%, this means that your MAF scaling or VE table is 15% inaccurate at that point and the fuel trims are fixing the error. Ideally you want your combined fuel trims to be as close to zero as possible but generally +/-3-4% is absolutely fine. 15% needs work.

thank you's for your replys, the car is a commodore ve r8 with a 427 stroker and running mafless tune, i do not have the ltft active at the moment.

the 14.7 wideband reading does fluctuate sorry about saying it is so steady, i meant to say as i am driving and it is fluctuating closely around the 14.7 mark i was noticing the stft errors. i will enable the ltft again and get back onto the dyno and redo the vve table rather than doing it by the wideband.

if i was doing it by the wideband should i then disable both stft and ltft so as to get a more true afr error?

your help is much appreciated to all.