Okay so what would cause a pcm to change the commanded AFRs while cruising? I have the stoich AFR set at 14.32 and while logging I saw where the commanded AFR changed and went to 15.92, down to 12.77, then back up to 14.32. All this happened at idle... WTF?

 

On the tahoe?

 

Yep!! And its not flex fuel related. I have turned all that **** off and it still goes wack

 

Id love to post todays log but the site wont let me upload it for some reason...

 

Weird, what ECM does it have?

 

E38. Ive been working on two different trucks with the E38 ECMs. Both changing commanded AFRs.. Nothing but a pain in my *** lol

 

I have the E38 and it does what its told...but I have been fighting with a P59 doing that same thing. Right now I'm wondering if its an O2 sensor thing...

 

See I thought it was an O2 also, but it looks to be working properly... My fuel trims are crazy out of wack, thought I may have had a vac leak. Looked all over and cant find a problem...

 

Best I can do for now

 

I believe that is an emissions test. Does it go lean for a little bit then rich for a little bit then back to stioch?