Weird AFR Variance test in 0411 PCM 12212156 OS Datalog.
Just ran across this and notice it in a datalog for the first time. What is the PCM searching for??? Is it part of the catalyst efficiency testing or perhaps something with the 02 sensors and closed loop fuel control or perhaps both?? All I know is my cammed L31 doesn't like it much at all. I actually felt the shudder in the idle when this happened and thought it was an odd feeling event and searched for it in the datalog. The PCM leans out the mixture for 2 1/2 seconds, then bumps it richer for 2 1/2 seconds, then levels back off where it was to start with. The whole event was about 5 seconds overall. I noticed the test right after the engine had fully warmed up on the highway and I had exited the highway and was stopped at a traffic light. The test happened almost immediately after the engine returned to idle and the VSS registered zero.
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