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2013 Sierra 5.3 AFM MPG

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I bought my current 2013 Sierra 5.3 ltr from an older gentlemen w/4K on the odometer in 2014.  Truck now has 80K on it and has always averaged about 13.5 mpg.  The best I've ever seen driving 60 mph on highway in traffic is just under 16 mpg.  My truck has the code in the glove box which verify's it has AFM.  I assume it must have been turned off prior to my getting the truck.  Is it possible that the AFM was turned off? 


Also, the engine is burning about 1 1/2 quarts of oil every 5K.  That's using mobile 1.  Everything I've read on this forum says that's normal, but my last truck 2000 Sierra 5.3 burned very little oil even at 200K.


I talked to my buddy that has a 2023 Sierra 5.3 ltr w/AFM and the best he has seen driving on the highway is 26 mpg.  Night and day difference is MPG vs my truck.  

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Yes, it's possible that the AFM could be deactivated...only way to really know (if you don't have the capabilities to read the programming) is to ask the previous owner.  But, with 4000 miles on it when you got it, I doubt it was deactivated.  When I had the lifters/cam replaced due to the ingenious AFM crap and deactivated that mess, I went from about 17 mpg up to a little over 18 mpg


The oil consumption rate is par for the course with this generation of 5.3s.  There is a night/day difference in the pre-AFM engines and the AFM engines in oil usage.

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On the dash just click that button to show the instant fuel mileage, it should show V8 mode and V4 mode.


My Silverado did and so did any other truck from that era that had the dash buttons. If it never switches to V4, then it was turned off. I had no trouble getting 20-21 on the freeway with mine and avg about 16-18mpg if I did mixed driving. Even when I disabled the AFM, I still got 20mpg on the freeway with ease.

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