Does anybody know of any disadvantages to GM'* active fuel management?

No Bonnevilles have Active fuel management, so off to the lounge.

None... :?

Agreed, active fuel management is great. What kind of disadvantages were you thinking of?

A few months ago I found an article on the internet saying active fuel management was somehow harmful to the engine. Now I can't remember exactly what it said and I have no idea where I found this article.

Unless upper cylinder lubrication is completely dependant on fuel additives, I can't think of any real issues. Alternating which cylinders are active should take care of anything I can think of.

Instead of working on transmissions and gearing for fuel mileage, they manipulate the combustion engine with "active fuel management" cylinder de-activation and rely on electronics as a gatekeeper. WAY to many of these engines have failed over the years; look at all of the class action lawsuits and AFM issues on the internet.................

It'* mostly okay.

Before anyone clobbers me: In the GM world, there are millions of AFM engines on the road in vans, pickups, large SUVs, mid-size SUVs, sports cars, and even a few RWD and FWD cars.

Yes there is a prevalence of them with severe issues. The number with severe issues is significant but not anything like 25% or 50% or 90% of all AFM engines built. The main issue I've seen on the interwebs (and on a friend'* 2008 K1500 5.3) is oil consumption. It appears there are a few that have progressed to major engine damage due to oil starvation related to AFM-specific parts and design.

If someone has real failure counts versus production counts I'd love to see them.

Anyways, in a nutshell it is mostly good and functions seamlessly, with some amount of mechanical issues on some of them.

Reliability from a theoretical standpoint: less air processed by the air filter and all sensors, less fuel combustion means less heat management, less carbon build-up, less injector cycles on the AFM-enabled cylinders, less processing of exhaust by the catalytic converters, and less exposure for oxygen sensors. The valves end up closed on the AFM cylinders so there isn't any great metallurgical concern with heat cycles of the metal parts involved or uneven block heating.

In reality, the downside has been related to oil consumption and starvation, and based on the numbers I have to wonder if a bunch of the related parts are slightly defective from the manufacturer . . . or if GM relied too closely on the "edge" of a specification in the design. For the latter, the example that comes to mind is the timing chain issue on the GM 3.6 V6. GM relied on lubricity continuing at higher oil-change intervals than real-world use could handle, hence timing-chain stretch, then a CEL then an expensive recall on affected vehicles. Something similar may be the case with the AFM oil-consumption and reliability issues.

I have been seeing things on the internet related to lifter issues with AFM. When AFM "engages", solenoids activate oil pressure to be introduced through small passageways to spring loaded push pins in the lifters, which causes the lifter to collapse and not engage the push rods. At the same time the computer stops fuel to the now inactive pistons/valves. This happens thousands of times and after a while these lifters can fail. Either the push pins partially engage or don't engage at all. Depending on the situation, this can cause misfiring or damage to push rods, cam shaft, etc... There is a device called an AFM disabler that you plug into your OBDII port which tells the computer to not activate the system when it normally would. I personally have tried it and it does work. I only used it for a tank of gas and now I am back to not using the disabler. Put it this way, I am not sure at this time if the disabler does more damage than not. I just don't know. I am interested if anyone else has any experience/knowledge on this topic. Using the disabler does make a noticeable difference in fuel mileage. At least 2 to 3 mph difference.

​​​​​​​Wow, this thread is a blast from the past!

It is interesting to see what was said in 2018 and 2008 about AFM as it progressed through the ages.

Your AFM disabler won't cause any mechanical harm. AFM engines start in all-cylinder mode and often run in all-cylinder mode as they do their job. Your disabler is simply telling the PCM to never do any AFM stuff. If there was buildup of an issue or issues in your vehicle prior to your disabler, they may still pop up, but your disabler would likely extend the time before that happens by quite a bit.