air fuel goes super lean

[apex2112]

I was helping a friend tune his mostly stock truck and was just starting a log to dial in the MAF when all of the sudden it went super lean.
My first thought was the sensor went bad, so I stopped and loaded a speed density tune but had the same issue of being lean.
I could set the air fuel ratio with the bidirectional controls and it would fuel correctly.
Any ideas why it would all of a sudden go super lean?
I have the tune setup to not use the long and short fuel trims so I don't see how it could be bad o2's
I have the tune and log file attached that first had the issue.silverado 03 maf tuning.hptmas 12_15_18 3rd bad.hpl
just realized i didn't save the log where the problem first occurred. the one attached is after flashing back to a speed density tune.

Thanks

[robschwieb]

You say you have the tune setup to not use the ST or LT fuel trims but from my understanding (and limited experience) if they are disabled they should always show 0? Your tune is still setup for CL when ECT is over 131 degrees. Looking at your log, bank 2 is really acting up. I think you are still in closed loop with a failed o2 sensor on bank 2.

Try setting your Closed Loop enable to 284 across the board and see what happens.

[lukearmstrong1990]

its going lean because the bank 2 oxygen sensor is removing 30+% of fuel as shown on your log. I would suggest this is a bad 02 sensor or you have an intake or exhaust leak on bank 2.


to stop it just disable closed loop and STFT and tune purely from wideband data

[apex2112]

I thought the O2 was already disabled, not able to check now but will later a report back.
Thanks for the help.

[apex2112]

Just checked the tune again and yes I did forget to set closed loop enable to a higher coolant temp.
Whats really odd is I had run some logs earlier and it always showed the fuel trims zero see attached.
I'll reset that enable temp. higher and try again.
Thanks again for the help
mas 12_15_18 2st.hpl