Hello,
please excuse my bad english, i am german.
My problem is, that I get sometimes codes about bank 2 too rich and catalic converter bad at bank 2.
I have changed many things: Sparks, Coils and many Sensors without any effect.
By scanning the PID's with Forscan i am wondering why the STFT are correctly about +/- 5 %, but LTFT
are -15-20 % on Bank1 and -20-25% on Bank 2 changing exactly synchron with encreasing and falling rpm in the range of 5 % (both LTFT).
I thougt LTFT's where only changed by the PCM after some minutes and not in seconds!

What is the reason for this?

 

It’s normal for LTFT to change with RPM because the PCM has learned those values from the drive cycle. The STFT supposed to (attempt) to return to a normal % once LTFT have adjusted to the new rich condition - don’t overthink it just fix the rich condition and the STFT will adjust those LTFT back to normal if left alone.