Jet DST fuel trims disabled

I posted a similar thread over on LS1tech this morning.

Car in question is 1996 LT1[OBD2] M6. All internals are stock. The car came with the cold air intake already mounted. The car starts well and idles at 1100 RPM and drops eventually to 800 RPM once warmed up. The car idles between 29 and 30 K PA. Tuning with Jet DST.

I’ve stumbled across an interesting situation whereby depending on the values I put into the open loop idle table The fuel trims may be disabled.
for instance, when modifying the 25K KPA and 30 KPA cells , if I leave the values relatively rich once the car goes into closed loop the fuel trims are active and wide band shows it reaching the desired 14.7 or thereabouts.

If I set these values closer to 14. 7 my initial idle is where I want it [14.4 to 14.6] but once the car goes into closed loop the fuel trims are locked at zero and the AFR drops to 13.8.

this is all running with the MAF plugged in. I’m not opposed to the idea of running speed density. But at the moment all I’m really trying to accomplish is a clean idle.

Jon

Just out of interest, I added a bit more spark advance to the Closed TPS spark table.
With no other changes once the car hit closed loop the fuel trims stay locked at zero and it was idling rich (13.4ish -13.8).


Stepped back to an earlier calibration and , sure enough, fuel trims are back functioning again.

There must be some threshold that I’m crossing as I make changes.

Jon