DFM and lifters question?

Anacortes Army Guy · October 22, 2021

7 hours ago, Jsd said:

Someone above misunderstood me about mileage. I was getting 21 mpg and after the Range delete it went to 17 mpg.

It was me...

newdude · October 22, 2021

18 hours ago, Jsd said:

Also, if 5 out of 50 trucks had a lifter problem that is 10% , which is a lot.

I should also add that 2 of the 5 were trucks bought elsewhere. I forgot to clarify that.

Gagliano7 · November 10, 2021

I didn't lose any mpg maybe 1 mpg by deactivating afm on my 2018 6.2 and by trans shifts perfect with afm off.

KARNUT · November 10, 2021

3 minutes ago, Gagliano7 said:

I didn't lose any mpg maybe 1 mpg by deactivating afm on my 2018 6.2 and by trans shifts perfect with afm off.

I had the same experience with my 14 GMC. I did multiple test going the same MPH over the same HWYs. No difference on or off. You would think by now there would be more of a difference. Of course there are people who drive under the speed limit who will claim otherwise. At 55 mph I got 24 mpg with it off with a 345 gear. I still believe under controlled conditions for the purpose of satisfying the EPA they hit their numbers. The real world is something else. The biggest laugh I got was riding in my father in law’s new CRV. It had stop start. Really? I get 30mpg in town with our 15 CRV. I actually get a mpg less at 72 mph. I’ll never get a cylinder deactivation vehicle. I’ll just rebuild what I have. I've done it with classic cars. I’ll do it as needed with my Avalanche.

TxTruckMan · November 10, 2021

I don't get the logic of trying to baby your truck to prevent an issue with faulty parts. If the parts are bad, they will fail eventually. I'd rather they fail early on when my truck is still under warranty instead of at 36,001 miles when I have to foot the bill myself. Just drive it like you stole it and let the warranty do its job.

Adamace1 · November 11, 2021

8 hours ago, TxTruckMan said:

I don't get the logic of trying to baby your truck to prevent an issue with faulty parts. If the parts are bad, they will fail eventually. I'd rather they fail early on when my truck is still under warranty instead of at 36,001 miles when I have to foot the bill myself. Just drive it like you stole it and let the warranty do its job.

Powertrain warranty is 60,000 miles.

newdude · November 13, 2021

On 11/10/2021 at 1:53 PM, TxTruckMan said:

I don't get the logic of trying to baby your truck to prevent an issue with faulty parts. If the parts are bad, they will fail eventually. I'd rather they fail early on when my truck is still under warranty instead of at 36,001 miles when I have to foot the bill myself. Just drive it like you stole it and let the warranty do its job.

Fair point.

However.

At 60,001mi (powertrain is , its out of your pocket. If AFM/DFM was disabled from day one, the chances of failure is near 0% (not 0% but near 0).

Grumpy Bear · November 13, 2021

On 10/21/2021 at 10:11 AM, Amcguy1970 said:

The failure rate is in the decimal of a percent, for the few you hear about on the forums with how many members are on here and all the millions that have been sold it is probably like 0.01%. People need to stop asking questions that no one knows an exact answer to and stop reading too much in to the forums, it just makes a mountain out of a mole hill. Follow the maintenance schedule and chances are incredibly high you won't have an issue. If it were a bigger problem the 800k ish per year trucks GM has produced with these motors there would be a ton more complaints on here about them, but you hear of like 1 or 2 a month it seems...

Tyler

99% of the time I would agree with you Tyler but in this case the schedule is still to long. IMHO naturally. Still your point is on point. Care for it an care for it well.

newdude spoke of the 2.4 motor ring issues. A case where the OLM suggested 7.5K number is far to long. Where even 5K OCI's with a Dexos oil (QSUD) was still to long. The issue with that motors rings are a lack of enough drain back space in the control rings land area. The oil moves to slow and degrades. An engineering issue that can only be overcome with even more frequent oil changes OR an oil with a HUGH detergent package OR a rebuild with a piston with more drain area like Seal Power from Jasper Engines design

In the case of AFM/DFM the same choices apply WHEN NOT part of the bad lifter dates.

On 10/21/2021 at 12:48 PM, AirForceAngler said:

That's still a huge drop in mileage. I disabled the AFM in my 2016 Suburban and hardly noticed a change in MPG at all.

The DFM will have more impact in town than AFM did and most AFM active motors are driving to fast to keep the system active enough to make a difference. In my truck 8-10% difference. I drive 55 mph. For a guy driving 70 mph... :dunno:

If you look at the EPA numbers for a 5.3 AFM vs a 5.3 DFM you will notice that the difference is in the city number not the highway number.

I have no problem believing his numbers.

kmeleon · November 14, 2021

On 11/13/2021 at 10:29 AM, newdude said:

Fair point.

However.

At 60,001mi (powertrain is , its out of your pocket. If AFM/DFM was disabled from day one, the chances of failure is near 0% (not 0% but near 0).

I don't understand this logic... If you disable dfm this doesn't drop the chance of failure to zero... this doesn't remove the faulty parts from the engine. The lifters are still problematic even though they're not be activated. Am I off base here?

Edited November 14, 2021 by kmeleon

newdude · November 15, 2021

13 hours ago, kmeleon said:

I don't understand this logic... If you disable dfm this doesn't drop the chance of failure to zero... this doesn't remove the faulty parts from the engine. The lifters are still problematic even though they're not be activated. Am I off base here?

I said near zero. I never said zero. But 99% if its disabled, you won't have a failure. A bunch of 5.3's the past few months have been built with DFM non functional due to the chip shortage and will 99% never have a lifter collapse issue.

If the AFM/DFM system is disabled, that means there is no oil being flowed to the locking/unlocking pin. They are always set in the lock position, and the solenoids are commanded off and will send no oil.

IF. And a big IF. The pin failed, or a solenoid somehow started to leak and flow oil to a lifter, then there would be the super, super small chance it could fail a lifter.

The failures however happen during normal AFM/DFM operation. The pin doesn't lock back up, the pin unlocks when its not supposed to and causes the cylinder to disable in V8, a solenoid starts to operate when it shouldn't or fails when it shouldn't.

I have almost 40K on my truck, AFM disabled for 38K of them. Zero lifter failure, zero lifter tick, etc.

UncleDave · November 15, 2021

I have a 2019 with the 4.3 V6 that has AFM. Supposedly it uses the same exact lifters and AFM solenoids as the V8. I haven't heard of lifter failures on these, but the there are far fewer V6 trucks sold or in service. Mine likes to tick especially when cold, as usual I was told that's normal. Personally I know of no-one who has experienced lifter failure on their 5.3, neither AFM nor DFM. I was considering trading up for a 5.3 but for various reasons might go with a 3.0L Duramax instead.

Edited November 15, 2021 by UncleDave

newdude · November 15, 2021

16 minutes ago, UncleDave said:

I have a 2019 with the 4.3 V6 that has AFM. Supposedly it uses the same exact lifters and AFM solenoids as the V8. I haven't heard of lifter failures on these, but the there are far fewer V6 trucks sold or in service. Mine likes to tick especially when cold, as usual I was told that's normal. Personally I know of no-one who has experienced lifter failure on their 5.3, neither AFM nor DFM. I was considering trading up for a 5.3 but for various reasons might go with a 3.0L Duramax instead.

4.3 uses the same lifters, same solenoids but they are on a different VLOM (because V6).

Bit of a tin foil hat theory but the 4.3 uses 5w30 where the V8s are 0w20. 0w20 perhaps is too thin of an oil on these engines, thus when run on an extended drain interval, its losing too much viscosity and thinning out further leads to oil aeration. That and or severe use (towing, high rpms, etc.).

Here is a bit from this TSB that conveniently only covers V8s:

Quote

#15-06-01-002K

This may be caused by one of the following conditions:

Active fuel management (AFM) lifter that is mechanically collapsed and/or stuck all of the time.

Internal locking pin damage in the lifter, due to oil aeration.

Lifter that has collapsed and is stuck in the lifter bore.

The engine may have a bent push rod.

Grumpy Bear · November 15, 2021

1 hour ago, newdude said:

4.3 uses the same lifters, same solenoids but they are on a different VLOM (because V6).

Bit of a tin foil hat theory but the 4.3 uses 5w30 where the V8s are 0w20. 0w20 perhaps is too thin of an oil on these engines, thus when run on an extended drain interval, its losing too much viscosity and thinning out further leads to oil aeration. That and or severe use (towing, high rpms, etc.).

Here is a bit from this TSB that conveniently only covers V8s:

No tin hat involved newdude. As a general rule 5W30 is less likely to aerate. That said there are 0W20 oils with intense antifoam additives that work just as well in combating aeration. Red Line HP i.e. There are people and OEM's who like to see how close to the edge of the cliff they can walk. In doing so, occasionally someone falls off that cliff. Extended OCI's, GDI viscosity killing fuel dilution.....yea....no tin hat required. You are a thoughtful man sir.

Z45 · November 15, 2021

Mine failed at 11.400 miles and was on cruise at 55mph. Heard a strange noise and at first I thought I rode over something and tire was going flat but air pressure was holding. Came to a stop sign 1 mile later and truck was stumbling. GM dealer was within 1/2 mile so I pushed on and they took it in right away and were 99% sure what the problem was. They had all the parts in stock. Drivers side replaced, was only w/o for about 1 day.

TRKLGND · November 18, 2021

On 10/21/2021 at 11:06 AM, AirForceAngler said:

Thanks for posting this info. I have a 2021 RST with the 6.2 that was made during the "bad" timeframe. I have about 2400 miles on it with no problems yet, even been pulling a 5,000# trailer frequently. I'm aware it can happen and have a good dealership to work with if/when it does. I just hope it doesn't happen when I'm halfway across the country pulling my little fishing boat!

When exactly is the "bad" timeframe?