My understanding of long trim vs short one is that the short trim readings will adjust the long trim after awhile right? For example my short trim readings are in the -5 to positive 7% max while the long trim will never ever drop below 10.9% and sometimes 17.2%. I was expecting the long trim to drop after seeing the short one hover around -3 to positive 5% range. I will attach images for this morning readings taken after engine is warmed up on idle.
You are right the STFT will replace the LTFT after a given amount of time. IIRC, the LTFT is the adjustment to the tune itself to compensate for fueling issues over a longer period of time. If the STFT is large for a long period of time (whether +/-), the LTFT will be adjusted accordingly. If the LTFT is at +17% and the STFT is steadily at -3%, then after a period of time the LTFT will drop to +14%, which should then move the STFT to zero. Then if the STFT needs to move to -3% again to adjust, after a period of time the LTFT would be moved to +11%. I don't know what the "time period" is for when it makes adjustments. I'm sure it's probably different per manufacturer's specifications.
It sounds like everything is doing its job, however, +10% is quite a bit of adjustment for LTFT. I believe 17% is pretty close to maxed out. I'd ensure the O2's are in good working order and the fuel system is clean (including injectors & fuel filter if equipped).
