Unsure if I want Tahoe with AFM

[wjburken]

We have a 2008 Denali without AFM. I rebuilt the engine...it did not have AFM components.

Nope. Neither did my 07 or 08. Your block had ports in it for AFM under the flat valley cover but that was it.

 

[PLohr]

I thought over the AFM question before we bought a vehicle without it. Best I could tell, AFM helped GM meet EPA combined emissions requirements but the benefits for the most part end there. On paper, the bean counters must have been satisfied that it would get out of extended warranty for nearly 100% of vehicles with few issues. What happens at 120k or 150k miles?

Overcoming the friction of four cylinders is not free of charge. Perhaps this is why many see little to no efficiency benefit from AFM.

High mileage vehicles, especially those not getting proper and frequent oil changes tend to be problematic. Will you be buying a vehicle with 50k miles? 100k or more? How many miles will you put on the vehicle? Higher mileage vehicles are better off without AFM, in my opinion.

Really, we each should look for SAE research papers to give us hard facts.

 

[wsteele]

I thought over the AFM question before we bought a vehicle without it. Best I could tell, AFM helped GM meet EPA combined emissions requirements but the benefits for the most part end there. On paper, the bean counters must have been satisfied that it would get out of extended warranty for nearly 100% of vehicles with few issues. What happens at 120k or 150k miles?

Overcoming the friction of four cylinders is not free of charge. Perhaps this is why many see little to no efficiency benefit from AFM.

High mileage vehicles, especially those not getting proper and frequent oil changes tend to be problematic. Will you be buying a vehicle with 50k miles? 100k or more? How many miles will you put on the vehicle? Higher mileage vehicles are better off without AFM, in my opinion.

Really, we each should look for SAE research papers to give us hard facts.

I think that is pretty accurate analysis.

Knowing the details of each model year’s failure results might be really helpful.

In my case, I have an ‘07 Yukon (original owner, anally maintained), which after 80K or so started burning oil. By 95K the rings were stuck enough that GM’s EFI cleaner bath procedure didn’t help and new pistons, rings, updated valve cover and relief valve deflector were installed. The engine now uses no appreciable oil and runs great (30K+ miles).

My dilemma now is the potential for one of the AFM lifters failing in a way that results in a larger issue. It would be really helpful to know the actual reliability profile of the AFM lifters versus normal lifters, in an engine that otherwise was well maintained (regular/filter changes, oil levels always maintained, etc.).

Without that actual data, it leads me to want to dump those lifters and delete AFM as a prophylactic measure for reliability.

Would I buy say a used ‘14 Yukon with 120K miles? If it checked out mechanically and the seller had all the service records? I probably would, but the deal would still have to be good enough to pay for an AFM delete kit install, just because I don’t know if the AFM lifters are actually less reliable in a well maintained engine that came with the updated valve cover and relief valve deflector new.

Sorry for the long post, it is hard to cover the nuances if you are a challenged writer.

 

[BG1988]

Welcome to the forum from Iowa.

If you can avoid AFM, that is preferable. If you need to get one, get a newer model (2013 or 2014). If you can find a ‘07 or ‘08 and possibly ‘09 Yukon Denali with the 6.2, they don’t have it.

Worst case if you get one with AFM is you can do a tune delete where it turns it off or a full delete where you remove the AFM parts altogether and get a tune.

Or, you can do what I’m doing. Change the oil regularly and hope it doesn’t act up.

the 4.8L does not have it.. the 4.8 was available on the LS only so you will have to pay for the options if you want those.. you will get a lot better mpg anyways with the 4.8L 20mpg depending on how you drive..

 

[wjburken]

I think that is pretty accurate analysis.

Knowing the details of each model year’s failure results might be really helpful.

In my case, I have an ‘07 Yukon (original owner, anally maintained), which after 80K or so started burning oil. By 95K the rings were stuck enough that GM’s EFI cleaner bath procedure didn’t help and new pistons, rings, updated valve cover and relief valve deflector were installed. The engine now uses no appreciable oil and runs great (30K+ miles).

My dilemma now is the potential for one of the AFM lifters failing in a way that results in a larger issue. It would be really helpful to know the actual reliability profile of the AFM lifters versus normal lifters, in an engine that otherwise was well maintained (regular/filter changes, oil levels always maintained, etc.).

Without that actual data, it leads me to want to dump those lifters and delete AFM as a prophylactic measure for reliability.

Would I buy say a used ‘14 Yukon with 120K miles? If it checked out mechanically and the seller had all the service records? I probably would, but the deal would still have to be good enough to pay for an AFM delete kit install, just because I don’t know if the AFM lifters are actually less reliable in a well maintained engine that came with the updated valve cover and relief valve deflector new.

Sorry for the long post, it is hard to cover the nuances if you are a challenged writer.

The mode of failure on the AFM lifters are when they don't fully pressurize in the split second that they have before the cam lobe comes around and they get jammed up or fully collapse. This delay in pressurization is due to a few things.
1) The VLOM is sluggish due to debris in the valves and ports
2) The VLOM is sluggish due to low pressure due to the VLOM bolts being loose or the orings not sealing the ports properly
3) The lifters have sludge in them that slows their pressurization.

By tuning out the AFM, you reduce the chances of #1 & #3 contributing to failures, but #2 can still be a cause so some folks have pulled the intakes and put in new orings, tightened the bolts properly and I think they have an improved VLOM design as well, but don't quote me on that.

I have had non-AFM lifters lock up and scrub the cam twice on my 2007. The first time resulted in a crate motor install at 150K. The second time was at 270K and I was able to just replace the cam and lifters, along with all the other "while I'm in there" stuff like the VVT phaser and actuator, timing chain, oil pick-up o-ring, etc.

The biggest thing you can do, no matter if you keep AFM active, do a tune delete or a full on AFM delete with cam and lifters, is keep your oil clean.

 

[BG1988]

I thought over the AFM question before we bought a vehicle without it. Best I could tell, AFM helped GM meet EPA combined emissions requirements but the benefits for the most part end there. On paper, the bean counters must have been satisfied that it would get out of extended warranty for nearly 100% of vehicles with few issues. What happens at 120k or 150k miles?

Overcoming the friction of four cylinders is not free of charge. Perhaps this is why many see little to no efficiency benefit from AFM.

High mileage vehicles, especially those not getting proper and frequent oil changes tend to be problematic. Will you be buying a vehicle with 50k miles? 100k or more? How many miles will you put on the vehicle? Higher mileage vehicles are better off without AFM, in my opinion.

Really, we each should look for SAE research papers to give us hard facts.

I see a 7 mpg difference with AFM only when using 91 octane
18.5 to 25.5-25.6 on the highway BEST i had ever done was 31.1 mpg

with 87 octane it's pretty useless it's exactly the same mpg as v8 only with the 4 speed gear set...

despite having the EVT SOD gear it will end up in a hyper rapid loop between v4 and v8.. and the SOD gear is never used, that equals death to the engine..

 

[wsteele]

The mode of failure on the AFM lifters are when they don't fully pressurize in the split second that they have before the cam lobe comes around and they get jammed up or fully collapse. This delay in pressurization is due to a few things.
1) The VLOM is sluggish due to debris in the valves and ports
2) The VLOM is sluggish due to low pressure due to the VLOM bolts being loose or the orings not sealing the ports properly
3) The lifters have sludge in them that slows their pressurization.

By tuning out the AFM, you reduce the chances of #1 & #3 contributing to failures, but #2 can still be a cause so some folks have pulled the intakes and put in new orings, tightened the bolts properly and I think they have an improved VLOM design as well, but don't quote me on that.

I have had non-AFM lifters lock up and scrub the cam twice on my 2007. The first time resulted in a crate motor install at 150K. The second time was at 270K and I was able to just replace the cam and lifters, along with all the other "while I'm in there" stuff like the VVT phaser and actuator, timing chain, oil pick-up o-ring, etc.

The biggest thing you can do, no matter if you keep AFM active, do a tune delete or a full on AFM delete with cam and lifters, is keep your oil clean.

Boy, that is some bad luck with lifters.

I didn’t think my ‘07 (LMG) came with VVT. Did you get the VVT with the crate motor?

 

[wjburken]

Boy, that is some bad luck with lifters.

I didn’t think my ‘07 (LMG) came with VVT. Did you get the VVT with the crate motor?

I had the 6.2 in my Denali so it had the VVT and the crate came with the VVT as well. The crate had a 100K warranty and the lifter gave up the ghost at 120K. I got a quote of $3000 just to diagnose and confirm it was a bad lifter so I did the work myself and it was the #5 intake lifter that locked up and chewed through the hard candy shell and into the soft nougaty center of the cam shaft. Ended up costing me $2000 by the time I got the new cam, new timing chain, tensioner, VVT stuff, lifters, head bolts, gaskets, etc. Got to buy the VVT phaser twice due my butter fingers dropping the first one and having it grenade all over my garage floor.

 

[wsteele]

I had the 6.2 in my Denali so it had the VVT and the crate came with the VVT as well. The crate had a 100K warranty and the lifter gave up the ghost at 120K. I got a quote of $3000 just to diagnose and confirm it was a bad lifter so I did the work myself and it was the #5 intake lifter that locked up and chewed through the hard candy shell and into the soft nougaty center of the cam shaft. Ended up costing me $2000 by the time I got the new cam, new timing chain, tensioner, VVT stuff, lifters, head bolts, gaskets, etc. Got to buy the VVT phaser twice due my butter fingers dropping the first one and having it grenade all over my garage floor.

Got it, I probably knew that and just forgot it along the way. Catching up to all this stuff is like drinking from a fire hose.

My alternative plan is to leave the engine be, leave the Range deleter in and do a reman crate if things go bad down the road. I have the tools and probably enough mechanical skill to pull off pretty much any type of repair, what I lack is the initiative when I can just tell that young bright tech, “let’s put that crate motor in”. I think bending over an engine bay for more than a day or two, might not be in the cards.

Who did you go with on the reman?

 

[wjburken]

Got it, I probably knew that and just forgot it along the way. Catching up to all this stuff is like drinking from a fire hose.

My alternative plan is to leave the engine be, leave the Range deleter in and do a reman crate if things go bad down the road. I have the tools and probably enough mechanical skill to pull off pretty much any type of repair, what I lack is the initiative when I can just tell that young bright tech, “let’s put that crate motor in”. I think bending over an engine bay for more than a day or two, might not be in the cards.

Who did you go with on the reman?

I think your plan is solid and understand the motivation/initiative thing.

As for the reman crate, I went through GM as I had the work done at a GMC dealer. The motor took a crap on my wife and I was out of town and the dealership was only a block away so I asked them to take a look. First time I used them but they are stand up guys and have had them work on my SUV's anytime I need a dealer do something.