Disable the AFM or not????

[swathdiver]

I have an 09 5.3 6 speed that is new to me with 150k. It was using a qt per 1000 miles. Tuned it and disabled the afm, added 30 hp, and get over 20mpg highway consistently.

Hey Butch, is that a regular length or the short one? 2WD or 4WD? At what speed do you get 20 mpg? I've never seen 20 mpg with mine; working on it though.

 

[harbison]

I have a 2009 GMC Yukon XL 5.3 2WD. 223K miles, 1 owner. I would recommend having an AFM delete done by someone who tunes engines. Oil consumption and gas mileage are not the major concerns. Valve lifter failure is what you should be concerned with. Half of the lifters in your engine are AFM lifters meaning they collapse when your engine goes into V4 mode. When these lifters get stuck, you have to tear the engine down to the block to replace them. GM has a TSB on this problem.