o.k. here it is, i've been thinking that gm is putting active fuel management on all the gassers. why hasen't anyone done this to a diesel??? is there any reason that it can't be done? i would think that you could kill the fuel to 2 or four cylinders depending on your throttle input(tps). i think that our trucks could maintain highway speeds on 4 cylinders just fine. if someone smarter than me could figure out how to do it i think we could be into the high 20's mpg wise. plus one could make a fortune. i would have done some research on this myself but i dont get along with the computer stuff too well.
o.k. my thought is done and over.

Right now I think it is a combination of the already present fuel economy benefit of diesels and durability. Right now AFM in the gas engine operates by having the lifters not operate the valves and by shutting off fuel injecctors. With the diesels, I think they might be concerned with the durability of the parts because of the higher temps it might see as well, the Duramax does have two valves per lifts so there would be more spring pressure to overcome when operating normally.

Now this is just my best guess, but it would be great to have others chime in on this.

Mods might consider moving to the Fourth Generation D-Max listing.

o.k. i guess it's not possible???

Possible ?? yes...

Expensive yes

You would have to redesign the entire cylinder head assembly with something similar to a jake brake setup. Only holding the valves open instead of closed. Then, how do you keep the valves from hitting the pistons and what about the massive amount of air that the cylinder is pushing? Were does it go? What about the exhaust or intake gasses backfeeding into that cylinder via the open valves??

There would be alot of engineering involved.

As has been previously noted - it's not just about shutting off fuel, you have to "vent" the defueled cylinders to stop compression and parasitic loss. With the higher compression of the diesel and the more "energetic" valve train it would be a major effort that probably would net less gain than in a gasoline engine. We're already more fuel and thermally efficient.

10-4. i was just wondering about it. i guess if it was that easy it would have been done already. it isnt a bad idea though, i wonder if they considered it on the 4.5?

http://dieselplace.com/forum/showthread.php?t=195160

There's some reading on this topic. Try the search function! its great!

Actually i asked a mechanic about this the other day and he suggested that it had more to do with the common rail fuel delivery system not being only electronically activated, but also oil fired.

Oil fired? I believe your mechanic friend was mixing Bosch HPCR with Ford Navistar, which uses pressurized engine oil to pressurize and fire the injectors. HPCR has a truly electronically tripped injector on a "high pressure common rail" at 10 to 30K psi and is not "oil fired."

HEUI, Hydraulic Electric Unit Injector, is fords method on the earlier Power Strokes. I don't have the info on the exact operation of them right in front of me, but it would be much more difficult to do with that type of injector.