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.