MAP sensor, catalytic converter and AFM/DOD

[ArthurC]

This is my very first post, I hope it makes sense and might help someone else who is having the issue I had.
 

I bought a used 2012 GMC Sierra 1500 with a 5.3. After a couple weeks I got an error message about my bank one upstream O2 sensor, cylinder 4 misfire and occasionally a random misfire, I forget the specific codes. I found a damaged spark plug so I replaced all the plugs and wires along with one coil pack that was damaged. The truck immediately ran better but it went into V4 mode more often than it did before the plug swap and O2 sensor replacement. I also got two new codes, MAP sensor performance and bank one catalytic converter efficiency. I drove the truck for several weeks but nothing changed so I replaced the MAP sensor, but no help. Then I found a AFM/DOD disable device on Amazon for $50 and 190 positive reviews, so I bought it and installed it. I cleared the Obd codes before I installed it. I drove it on several long trips and my MAP sensor errors stopped, no more catalytic converter efficiency errors and my gas mileage has actually improved.
 

I said all of that to ask - why would disabling AFM stop those specific errors? Especially the MAP errors, I was beginning to think I either had a vacuum leak or one of my lifters was collapsed, just from what I read, I’m no mechanic. 
 

One other thing, disabling AFM has made such a difference in how my truck runs and performs. It doesn’t run rough and shudder, or sound like it’s missing and the exhaust doesn’t sound like a helicopter or randomly pop when idling. The accelerator still has a hesitation, I may purchase something like a Pedal Commander in the future to fix that. Thanks for your help and ideas.

[asilverblazer]

Sounds like you actually had a problem with the AFM lifter not collapsing properly and still engaging the pushrods - opening and closing the valves still. 

 

Now the problem is masked.

[ArthurC]

Thanks for your reply. Im hoping the AFM won’t give me anymore problems, that is certainly one of my fears with this model truck. When you say it’s masked do you mean it could possibly get stuck closed, the lifter, and wipe out a cam lobe or burn the valve seats? 

The truck has 230,000 miles on it, which seems like a lot for 10 years old, and I’m not sure this is the original engine. I bought it from a used car dealer and he believed it was a newer engine and transmission (before the Covid price insanity). It certainly runs great and has tons of power for 230k. Knock on wood, I haven’t had anymore issues with missing or running rough and it’s been almost four weeks.