Fuel trim numbers

[FFMan]

As I understand it, in a catalyst equipped car the ecu uses the lamdas at some points to control fuel trim.

So the initial fuel figure comes from the map utilising the load and speed to locate the right site in the map.

The excellent G33 document states trim can be +/- 20% but I can't work out from the memory locations etc documented how both long and short term figure is retrieved.

thanks

[blitzracing]

That trim figure is the amount of trim available as a mixture shift- so 100% long and short trim would represent a 20% shift in mixture as an extreme case. The ECU works out what its doing by applying small shifts in mixture until the probes switch states, then it reverses the process. If the probe spends more time in one state than the other, the ECU then slowly applies long term trim to try and get the probes switching evenly around the short term trim mid point. You can fool it by putting in a square wave in place of the lambda input and changing the mark space ratio of the waveform, and you can watch the ECU try and correct with long term it over a couple of minutes. The long term trim values are written to battery backed up memory, so you loose them if you reset the ECU. If you want the memory locations where the trim values are stored you are better reading the post on remapping the 14CUX or asking Colin or Dan Bourassa.

Edited by blitzracing on Tuesday 4th March 18:17