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Commanded AFRs randomly changing

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Old 11-21-2011, 06:13 PM
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Default Commanded AFRs randomly changing
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?
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Old 11-21-2011, 08:22 PM
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On the tahoe?
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Old 11-21-2011, 08:29 PM
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Yep!! And its not flex fuel related. I have turned all that **** off and it still goes wack
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Old 11-21-2011, 08:31 PM
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Id love to post todays log but the site wont let me upload it for some reason...
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Old 11-21-2011, 08:31 PM
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Weird, what ECM does it have?
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Old 11-21-2011, 08:34 PM
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E38. Ive been working on two different trucks with the E38 ECMs. Both changing commanded AFRs.. Nothing but a pain in my *** lol
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Old 11-21-2011, 08:36 PM
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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...
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Old 11-21-2011, 08:40 PM
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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...
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Old 11-21-2011, 08:43 PM
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Best I can do for now

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Old 11-21-2011, 09:26 PM
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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?
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