DFM disable yet?

Thomcat · October 9, 2019

23 hours ago, Robwcormack said:

Because of the proven issues AFM has caused, and because I have corsa exhaust and it sounds like ass when DFM kicks in. I really dont care about the fuel economy. I didnt buy a truck with a 6.2 for gas mileage

Previous problematic issues with AFM have nothing to do with DFM operation and likely the '19s are clearing out the last of them. First AFMs introduced in my '07 model year Avalanche had oil burning issues associated with poor valve cover/PCV valve, LOMA manifold design and oil discharge valve in the sump. Discussed in length on the Avalanche forums. Seems that improper location of the PCV valve takeoff and discharge spray from the latter onto colder running AFM cylinders clogged and froze the oil control rings on the pistons allowing oil into the combustion chambers and all related oil burning problems. Likely aggravated by that engine killing DIC because its algorithm in calculating oil changes did not compensate with more frequent changes to reduce, not eliminate, the amount of dirt in the oil sprayed on the walls. Valve cover redesign in '08-'09 eliminated the PCV valve problem and post 1/11 modifications to the AFM discharge valve shrouded its horizontal ports redirecting all oil downward into the sump and not onto the AFM cylinder walls.

DFM is a totally different animal relying on electronic control complexity rather than mechanical control complexity to control cylinder deactivation. No more intermediate LOMA manifold in the engine valley feeding the AFM half of the engine cylinders using a combo of half traditional lifters and half collapsible AFM lifters. DFM eliminates the AFM's Achilles heel, LOMA manifold and discharge valve, entirely substituting individual oil control valves for each cylinder mounted directly in the block and collapsible lifters on all cylinders. So now the ECU is in control of the oil feed to all cylinder lifters instead of the former AFM concept with the ECU controlling the LOMA which controlled oil feed to only the AFM cylinders.

https://gm-techlink.com/?p=11880

My guess is that with the more advanced and less mechanically complex DFM available, GM will be clearing out the last of their older AFM engines with the exception of the V6 and new 2.7turbo which remains AFM. Must be a reason why they chose to continue the AFM approach over later DFM on a newly introduced engine design....might have to do with the engine balance or harmonics to specific rpms for 4 cyls. which differ from those for I6, V6 and V8s.

Edited October 9, 2019 by Thomcat

J-man67 · October 9, 2019

Amazing information! Thanks for sharing that!

Sent from my SM-N975U using Tapatalk

Robwcormack · October 9, 2019

2 hours ago, Thomcat said:

Previous problematic issues with AFM have nothing to do with DFM operation and likely the '19s are clearing out the last of them. First AFMs introduced in my '07 model year Avalanche had oil burning issues associated with poor valve cover/PCV valve, LOMA manifold design and oil discharge valve in the sump. Discussed in length on the Avalanche forums. Seems that improper location of the PCV valve takeoff and discharge spray from the latter onto colder running AFM cylinders clogged and froze the oil control rings on the pistons allowing oil into the combustion chambers and all related oil burning problems. Likely aggravated by that engine killing DIC because its algorithm in calculating oil changes did not compensate with more frequent changes to reduce, not eliminate, the amount of dirt in the oil sprayed on the walls. Valve cover redesign in '08-'09 eliminated the PCV valve problem and post 1/11 modifications to the AFM discharge valve shrouded its horizontal ports redirecting all oil downward into the sump and not onto the AFM cylinder walls.

DFM is a totally different animal relying on electronic control complexity rather than mechanical control complexity to control cylinder deactivation. No more intermediate LOMA manifold in the engine valley feeding the AFM half of the engine cylinders using a combo of half traditional lifters and half collapsible AFM lifters. DFM eliminates the AFM's Achilles heel, LOMA manifold and discharge valve, entirely substituting individual oil control valves for each cylinder mounted directly in the block and collapsible lifters on all cylinders. So now the ECU is in control of the oil feed to all cylinder lifters instead of the former AFM concept with the ECU controlling the LOMA which controlled oil feed to only the AFM cylinders.

https://gm-techlink.com/?p=11880

My guess is that with the more advanced and less mechanically complex DFM available, GM will be clearing out the last of their older AFM engines with the exception of the V6 and new 2.7turbo which remains AFM. Must be a reason why they chose to continue the AFM approach over later DFM on a newly introduced engine design....might have to do with the engine balance or harmonics to specific rpms for 4 cyls. which differ from those for I6, V6 and V8s.

Wow! I know for a fact that the service techs at my local dealership don't even know all this stuff. Hell I had to tell the guy it had DFM and not AFM and he tried to tell me it was the exact same thing. I knew it wasnt, but I certainly didnt know the details like this. Very good info. At the same time, it seems like just more that can go wrong if it doesn't work properly when if I didnt have it I wouldn't have to worry with those problems. It blows my mind that this "feature" isnt optional, similar to the ECO button in many vehicles. If I want to use it and save gas, that's great, but if I don't I should have the option not to.

Zach-91 · October 9, 2019

This video goes into a little more detail about how the system works. Pretty neat stuff. Scary that there are so many moving parts but neat from an engineering standpoint. Coming from a 2015 (5.3 6spd) silverado with AFM to my 19 (5.3 8spd) with DFM there is a night and day difference in drive ability. Weird shifting aside, the lag and jump between afm activating was miserable. I had a diablosport lew tune the entire time I owned the truck to make it more enjoyable/driveable. On the new 19, there is a little delay in the time you step on the pedal and the power comes in but it is smooth. I can't feel the disabled cylinders like you could on afm