1st GM Product This Century!

[iamdub]

If you're in some hills in Colorado, you're not gonna see V-4 mode very often. For someone that does a lot of straight, flat and smooth highway driving it will have some benefit as far as a couple more MPG. For those 90% others, they should delete that shit before it deletes their motor. Electronically disabling it (Range device or custom tune) is a great start, but mechanically deleting it (replacing the AFM components with regular ones) is the best because you get rid of the failure-prone lifters.

 

[cekkk]

I'll be at a rim shop today for hub con rings that Costco pointed out were lacking when they replaced a couple tires on the 22 inch rims that had been put on the truck. While out I'll check on fixing the V4 problem. What is AFM and approx cost to replace?

 

[DenaliEd]

Welcome!!! Are you sure the Denali is 2WD? There's nothing on the AWD ones that say they're AWD...

 

[iamdub]

AFM- Active Fuel Management. It's when four of the eight cylinders shut down (V4 mode) to help increase fuel economy. The engine has to have a relatively low amount of load on it for it to activate- cruising on flat highway (or a steady decline), no headwind, steady throttle input, etc. Your driving habits and conditions dictate how much it's activated and if it does any good. Aside from those that live in flat, wide-open desolate places, it's more of a hindrance because almost as soon as you get to a steady cruise in V4 mode, you have to accelerate again or apply more throttle to maintain speed going up even the slightest incline. There's usually an ominous lag that's felt before it switches back to V8 mode.

All that's just the operation of it. The REAL problem is that the special lifters used on those four AFM cylinders are more complex than standard lifters and they are commonly known to fail. The symptoms/damage ranges from a misfire and no compression on a cylinder (usually repairable) to wiped-out cam lobes(s)/metal all throughout engine/scored bearings.

You can plug in a Range module that keeps the PCM from activating AFM and this is far better than nothing. Another option is to get tune, either from a handheld tuner or a custom tune and have it deactivated as one of the tuning parameters. If I were just gonna disable it electronically, I'd go this route over the Range because I could tune for other things for about the same or little more cost. The best way is to replace the AFM components with the non-AFM parts as if it came from the factory with no AFM. You can use all readily available OEM parts for this. It's also a perfect time to upgrade the cam for a little more power at a minimal extra cost. There are "kits" that contain everything needed to mechanically delete AFM. A tune will be needed afterwards to turn off AFM in the PCM's programming and to tune for the upgraded cam, if installed.

The AFM failure seems to be one of those "not if it happens, but when it happens" things. It might not happen in 80-, 100-, 150- or 200,000 miles. But it seems the risk elevates exponentially the higher the mileage. My opinion is that AFM is what made the LS engine go from a 300,000-mile engine to a 150- to 200,000-mile engine. The sooner you remove it, the better.

 

[cekkk]

Denali Ed, no, not sure at all. AWD is good news.

Iamdub, we tend to keep our vehicles ten years or longer. So while deleting AFM sounds expensive, so are engines. I won't be doing it myself. What price range would you think and can a good home mechanic do it? I have one. But also know new vehicles aren't easy, tool wise, if nothing else.

And finally, the rim shop said I'd have to have a hub ring fabricated because it's an odd size. He also said it wasn't necessary unless I was getting shaking at low speeds, which I'm not. Do you all agree?

A ND thanks everybody!

 

[HiHoeSilver]

If you want to know about AWD, just look under the front end and see if there are axles and a diff up there. Or check your RPO codes.

 

[iamdub]

Iamdub, we tend to keep our vehicles ten years or longer. So while deleting AFM sounds expensive, so are engines. I won't be doing it myself. What price range would you think and can a good home mechanic do it? I have one. But also know new vehicles aren't easy, tool wise, if nothing else.

The best estimate I could give for having the AFM deleted is around $1500 parts and labor. But, that can vary drastically by region and shop. A member here recently posted that his local shop is doing it all with tuning for $1,000. TSP has a kit (HERE) to which all you need to add is a non-AFM camshaft, either stock or aftermarket (performance cam). You should be able to find a stock pull-out cam for cheap on most any forum, particularly ls1tech.com. A competent, well-equipped home mechanic that's intimately familiar with the LS platform can surely perform the surgery. These engines are actually quite easy to work on. One of the biggest benefits is that there really aren't any "dumb tricks" to know such as using a special sealer on certain head bolts but not on others like there was on my Jeep. They also have O-ring seals everywhere- no traditional gaskets. In fact, many are reusable. The intake manifold is "dry", meaning it doesn't have coolant passages. You unplug the injectors and sensors, disconnect the fuel line(s), back out the bolts and take it away. No torn gasket material to scrape off and no coolant pouring out everywhere. Really, the hardest/messiest part is probably removing the fans and radiator for clearance to swap the cam.

And finally, the rim shop said I'd have to have a hub ring fabricated because it's an odd size. He also said it wasn't necessary unless I was getting shaking at low speeds, which I'm not. Do you all agree?

I prefer using the hub as a centering/load-bearing point instead of just the lugs where available, but I've never known of any failures not doing so. Always make sure the wheel's and rotor's mounting surfaces are clean. Hand-tighten the lugnuts while wiggling the wheel a little to be sure the nuts are centered and seated fully. Tighten a little more with impact or lug wrench in a criss-crossing pattern, tighten more from that, then tighten them to their final torque specs. The key is to tighten them in multiple stages, but evenly.

 

[cekkk]

Appreciate that, Iamdub. And googling around about whether that thing is AWD or 2WD, I ran into some interesting threads elsewhere. All Denalis are. Some are, some aren't. Not sure what's true. But a quick look underneath shows mine is AWD, full time. I imagine there is a slight mpg penalty. Expeditions are 3-way, 2WD, AWD and 4 wheel.

My plan is to first do a tune, then after we finish the purchase of our 2nd and probably last retirement home, get the V4 problem fixed the right way.

 

[iamdub]

Appreciate that, Iamdub. And googling around about whether that thing is AWD or 2WD, I ran into some interesting threads elsewhere. All Denalis are. Some are, some aren't. Not sure what's true. But a quick look underneath shows mine is AWD, full time. I imagine there is a slight mpg penalty. Expeditions are 3-way, 2WD, AWD and 4 wheel.

My plan is to first do a tune, then after we finish the purchase of our 2nd and probably last retirement home, get the V4 problem fixed the right way.

Yeah, usually 1-2 MPG less.

At 55K, you have some time. The best you can do to prevent an AFM failure is to do the same as you would for any engine: Use a good synthetic oil and quality filter (i.e. Wix/Napa Gold) and change it as needed to keep the internals clean and free of varnish and/or deposits. Maybe run a cycle of AutoRX to ensure it's clean and maintain it with a mild cleaner (MMO, Rislone, Seafoam- you pick your poison) a few hundred miles before an oil change every few OCIs. It's best to prevent any build-up rather than to try removing it. If you can keep the oil and it's passages spotless, then there shouldn't be anything to clog the tiny oil ports in the AFM lifters. Then the only failure would be from something breaking from a defect in design and/or manufacturing, which is something you can't do anything about until it happens.

 

[DenaliEd]

Good to hear that it is indeed AWD. I can't imagine a 2WD Denali would do well in a CO Snowstorm...