My current fuel trims - idle, 2000rpm, 3000rpm all no load

[Mudsport96]

An additional thought.... You read on the internet that the STFT and LTFT are added to get the actual trim that will be applied. Yes and no. My STFTs bounce up and down rapidly about +/- 2% -> +/-3%. Let's call it a 6% swing. I don't think the ecu would swing the fuel delivery 6% every second or so. Doesn't make sense. Probably the STFT values are gathered over ? 50 readings and an average is determined then some part of that average is used to adjust the LTFT.

I am not sure how often samples are taken for short term trims. And the long terms are the average of the shorts, again not sure when they are moved from ST to the LT file. Are you in a relatively flat area or have some hills? Could be that you are on and off the gas enough that it enriches more often.

 

[2006Tahoe2WD]

I am not sure how often samples are taken for short term trims. And the long terms are the average of the shorts, again not sure when they are moved from ST to the LT file. Are you in a relatively flat area or have some hills? Could be that you are on and off the gas enough that it enriches more often.

I've watched the LT and ST going up a steady incline recently and both seem to behave themselves - no big moves. When running on the flat I try to hold the pedal steady and watch the airflow in g/s and see if I can make it also steady then watch the trims and see what is going on. As I mentioned all could be working fine.
Another data point would be what others are seeing on LTs and STs at steady cruise. You may have posted that.

 

[2006Tahoe2WD]

Yesterday I tried displaying the Commanded Evaporative Purge and couldn't get it to work. That is a standard listed PID but for some reason it is not listed in OBDLink. So my experiment to compare trims to the purge air amount isn't going to happen right now.

 

[2006Tahoe2WD]

Yesterday (Thursday) I bought 10 gallons of 100 Oct gas at the 76 station here. $10/gallon.
This was mixed with about 4 gallons of 87 Oct. The fuel trims lowered a bit but at steady-state highway the LTs are about the same. The 100 Oct might also I have ethanol, this is unknown.
I'm still working on getting the OBDLink MX+ to report the Commanded Evaporative Purge.