Dfm work around

Moosebeavers · October 27, 2019

Just traded my 15 in for a 19', had a kid and wanted to switch from a quad to crew cab.

I never had issues with the AFM in the 15 but I know people who did, so I did the majority of my driving with the transmission in "M5" to keep it from going into 4 cylinder mode. It was nicer to drive around town this way as well. If I was on the highway, I would shift to 6th once the engine was at temperature.

I'm picking up my new truck in a few days and was wondering if you can do the same thing with the 8 speed and the new DFM system. Unlike the last gen, it doesnt show when its deactivated cylinders so it's hard to tell. Anyone now any work around yet or should I just wait for the DFM range to come out.

redwngr · October 27, 2019

If you can't tell by driveability that it's doing anything why is override necessary?

cltsig · October 27, 2019

Try it first. Really not noticeable now.

OnTheReel · October 27, 2019

Yes, you can run it in L7 if you hate DFM enough to lose top gear in your transmission and don’t mind clicking up every time you leave the house. But as others have said, it’s not very noticeable at all. Drivability is much better. Wouldn’t hang around waiting for a disable device, we are at 15 months already...

Hobey · October 27, 2019

2 hours ago, cltsig said:

Try it first. Really not noticeable now.

Is there any dash or display info that would tell me about the DFM and what it is doing and how many cylinders are running......txs

Edited October 27, 2019 by Hobey

OnTheReel · October 27, 2019

51 minutes ago, Hobey said:

Is there any dash or display info that would tell me about the DFM and what it is doing and how many cylinders are running......txs

Nope. Patterns are way too complex to give a readout for. You can pretty much assume any time the engine is warmed up and lightly loaded, and the trans is in “D” it will be dropping cylinders.

The other thing you can do as a learning experiment, get the truck moving at a constant lower speed (where it won’t be running in top gear no matter what). Then click from L7 to L8 (or L9 to L10 on a 10 speed) and then back down occasionally. The trans won’t downshift or upshift between the two, but you should hear and feel a slight difference. That is the DFM engaging and disengaging between the two gear selections. It won’t be active in L7 but will be in L8 (same, but with L9/L10 in ten speeds)...that makes it easier to pick up the DFM in other situations (not that it matters)...hope that makes sense.

Moosebeavers · October 28, 2019

14 hours ago, redwngr said:

If you can't tell by driveability that it's doing anything why is override necessary?

Longevity of the vehicle. I had a coworker who's truck spent way to much time in the shop due to AFM. If I can stop it while driving around town (where I dont need 8th gear anyway) then maybe i save myself a future headache.

Moosebeavers · October 28, 2019

Thanks for the replies, first time on this site, not sure of the protocols and took a minute to figure out how to respond...

Alot of my driving is in the city where the engine is doing a tonne of switching so keeping it in m7 sounds like it will work for me, I don't need 8th in town anyway. I'm in Canada where it's cold and the engine oil doesnt always get to temp before I start driving. My mechanic buddy had suggested driving around in m5 until its warmed up with my previous truck and who knows, it didnt hurt anything. The economy was negligible so I guess I will take the same approach on my new one. Cant wait to pick it up on Wednesday-crew cab Sierra elevation with all the options, I can even fit my dog kennel in the back seat.

Hobey · October 29, 2019

On 10/27/2019 at 7:57 PM, OnTheReel said:

Nope. Patterns are way too complex to give a readout for. You can pretty much assume any time the engine is warmed up and lightly loaded, and the trans is in “D” it will be dropping cylinders.

The other thing you can do as a learning experiment, get the truck moving at a constant lower speed (where it won’t be running in top gear no matter what). Then click from L7 to L8 (or L9 to L10 on a 10 speed) and then back down occasionally. The trans won’t downshift or upshift between the two, but you should hear and feel a slight difference. That is the DFM engaging and disengaging between the two gear selections. It won’t be active in L7 but will be in L8 (same, but with L9/L10 in ten speeds)...that makes it easier to pick up the DFM in other situations (not that it matters)...hope that makes sense.

Thanks, I will try that soon between L7 and L8...... Might wait till I hit the 850 km break-in as suggested in the owner's manual....thanks again

Stex · October 30, 2019

My concern with DFM and AFM is not how it drives but wear and tear on the mechanicals of the DFM/AFM. If I can cut down on the lifters constant collapsing/ un-collapsing and other mechanicals, is what I would be looking for. From what I have read the DFM, is more mechanically complex (more moving parts and levers) than the AFM.

GM had a long time to improve the lifters but the DFM mechanicals are all new. The AFM issues did not really show up till 40-90,000 miles. Still see AFM delete jobs in my friends repair shop, Mainly due to lifters. Runs about 2,500 as the heads have to come off.

Tune to turn off AFM/DFM, does not appear to be an option on the new models. I think range still claims to have the ability to turn off DFM.

Grumpy Bear · October 30, 2019

Freevalve Update Camless Engine

You ain't seen nothing yet!

I'll be first on the buss of a version of this in the 4.3 Gen 5 platform.

Jeb1300 · November 10, 2019

On 10/27/2019 at 6:57 PM, OnTheReel said:

Nope. Patterns are way too complex to give a readout for. You can pretty much assume any time the engine is warmed up and lightly loaded, and the trans is in “D” it will be dropping cylinders.

The other thing you can do as a learning experiment, get the truck moving at a constant lower speed (where it won’t be running in top gear no matter what). Then click from L7 to L8 (or L9 to L10 on a 10 speed) and then back down occasionally. The trans won’t downshift or upshift between the two, but you should hear and feel a slight difference. That is the DFM engaging and disengaging between the two gear selections. It won’t be active in L7 but will be in L8 (same, but with L9/L10 in ten speeds)...that makes it easier to pick up the DFM in other situations (not that it matters)...hope that makes sense.

My new 19 6.2 has a constant on/off jerkiness and drone when it is dropping cylinders. city or Highway? Just drove to St. Louis and back and it was terrible. It did not do this in the 1st 300 miles but now it is really bad. I just joined to research this and most say it is not noticeable on the new trucks but mine is bad and my 17's with the 6.2 you could not tell. I think I need to take it to the dealer and have it checked out, it is not enjoyable to drive the way it is. Such a quiet truck except for the on/off drone.

darks1d3 · November 25, 2019

On 11/9/2019 at 10:45 PM, Jeb1300 said:

My new 19 6.2 has a constant on/off jerkiness and drone when it is dropping cylinders. city or Highway? Just drove to St. Louis and back and it was terrible. It did not do this in the 1st 300 miles but now it is really bad. I just joined to research this and most say it is not noticeable on the new trucks but mine is bad and my 17's with the 6.2 you could not tell. I think I need to take it to the dealer and have it checked out, it is not enjoyable to drive the way it is. Such a quiet truck except for the on/off drone.

Mine is the same way. Barely noticed it on my 2014 but my 2019 is a different story. It's even worse in 4 Auto.

Jeb1300 · November 25, 2019

2 hours ago, darks1d3 said:

Mine is the same way. Barely noticed it on my 2014 but my 2019 is a different story. It's even worse in 4 Auto.

Dealer checked it out, said it is normal. Worst speed for it is 60-65. You can watch on the DIC as it dropped cylinders the mpg spikes, drone and rattle and jerkiness starts, then it loses to much power and more cylinders kick in and and it goes away. Reminds me of my 2012 Avalanche with the 6 speed, afm kicked in to early but you would hear deto , now it is a drone/ rattle. As good as they had the 6.2 8 speed in the 17 it is disappointing to go so far backwards.

J2Jones · November 26, 2019

I don't have any drone with my 6.2 but have definitely noticed the jerkiness on occasion. Generally not too bad at steady speed but if there's any traffic, the subtle throttle adjustments seem to set it off and you feel it.