I have a 2012 sierra 6.2, owners manuel says if you don't run 91 or higher octane fuel that the truck will feel sluggish. Does the computer retard timing do to spark knock and if so how do you get the computer to go back into high octane mode ?? I also have a 2010 ss camaro and there is a procedure where you pull 2 fuses and the computer will reset back to high octane mode. Just wondering if there is a fuse pull for these trucks ?? Thanks in advance Kirk..

 

Put gas in it and drive it the pcm will figure it out. Don't have a clue what the conditions are that have to be present for it to figure out the fuel it has in it. If I remember right I maybe think I heard at a gm school that the parameters for the pcm to figure out fuel it has in it occurs when the truck is filled completely to full with fuel.

 

That is why timing is pulled for the first ten miles (?) when tank is filled completely. The truck is determining what fuel is present, 87,89,91,93 or E85. No procedure needed besides filling your tank full, and driving it.

 

Thanks for your replies, just thought the 6.2 in the truck would be like the 6.2 in the camaro. Camaro5.com talks about once the ecm detects spark knock it pulls the timing back and it doesn't go back because the ecm can't tell what kind of gas is in the tank, so you pull 2 fuses and put them back in after a while and it resets the ecm, it made a differance in the camaro. Thanks again.