GM DOD/AFM Interesting Oil Observations

[tony1679]

I just wanted to share my personal experience with this technology. For those that don't know what this is, it's GM's cylinder deactivation system for "improving fuel economy."

I bought the Impala in my sig 1 year ago with 75k miles. The first month, I noticed a significant oil loss, and I knew it wasn't leaking. During 9k miles of using Synpower 5w30 (used since the first day I bought it) it consistently "used" a full quart every 750 miles. I changed the oil every 3k for this reason. That's 3 quarts added in a 3k interval, and a quart low when it was changed. Also, I averaged 23 mpg consistently, determined both by the computer and on paper (miles/gallons).

So after reading multiple forums I realized the oil consumption is common. GM officially states 1 quart every 1,000 miles is "acceptable" and beyond that they will perform consumption tests and correct problems. Their corrections consist of a "baffle to stop oil splash" (that doesn't work) and clean or replace piston rings (which also doesn't work).

I didn't want to play games wih GM or the stealership (especially considering I was no longer under warranty) so I took matters into my own hands. I bought a handheld tuner (Superchips Cortex). Most tuners have an option to disable AFM.

From day 1 on the tune to today (97k), IT HASN'T LOST A SINGLE DROP. The icing on the cake is my fuel economy is actually slightly BETTER! I now average 23.5-24 consistently.

Based on this evidence, my opinion of DOD/AFM is obvious (and stated In my sig). I hope this gives some insight to potential/current GM owners, and I would like to hear a few thoughts on this.

 

[JHL88]

I bought a range AFM tuner for my "13 silverado. I went from 16.2 mpgs to 16.8 mpgs mixed driving with AFM turned off.

 

[A_Harman]

YMMV

 

[zuluplus30]

Our 09 Silverado was under warranty and had the TSB done. It drank oil like water. Lots of times as the consumption gets worse for long enough it gums the rings so bad that even deleting the AFM with a tuner wont help. Congrats on catching yours before that happened. If I was to EVER buy another AFM motor, I would have a tuner waiting the minute I drove it off the lot.

 

[Propflux01]

I think it has to do with cylinder pressure. During a firing stroke the pressure of combustion helps keep oil from getting past rings. I've worked on vehicles that lose a coil and it seems on those cylinders the plugs are usually slightly wet with oil.

 

[lexus114]

that afm stuff didnt work in the 80s either. so why would they even consider it now? that is a bad idea no matter how much electronics have improved.

 

[PReal]

My consumption dropped with the switch from valvoline synpower to penzoil ultra. My oil level hasnt dropped in 3700 miles.

 

[tony1679]

^Glad it worked for you but it won't for the majority with this problem. I've used VSP across multiple makes and models with stellar results. But I don't want to start a brand war. That's not what this topic is about.

 

[440Magnum]

I think there's something more going on here. GM AFM works almost identically to Chrysler MDS. While MDS has had some issues (harmonic vibrations overstressing timing chain components in some 5.7L applications, currently being addressed by a recall/TSB program), I don't see many reports of it causing oil consumption. The deactivated cylinders just repeatedly compress the same charge of air over and over, there's little reason to expect increased oil consumption unless its something else going on with the oil control ring package because of the lack of combustion heat, or a change in ring motion in the ring slots.

I'd experiment with oil brands, particularly using oils that resist gumming and deposit formation with top grade base-stocks- something like Pennzoil Ultra Platinum or M1, or a boutique oil. Deactivate AFM it if you want, but overall AFM/MDS whatever you want to call it is a very simple and reliable system these days, totally different from the Cadillac V8-6-4 implementation of the 1980s- any comparison to that system is spurious because the design has nothing in common.

 

[Ken2]

Quote:
If I was to EVER buy another AFM motor...
What has GM done to earn your future business?

 

[tony1679]

440Magnum - Why would I want to experiment with different oils when the problem has been solved? To keep AFM on and get less mpg? Lol

But I do agree with the Cadillac thing. Totally different. But I also agree that they need to quit with cylinder deactivation altogether.

 

[tony1679]

Originally Posted By: 440Magnum
While MDS has had some issues (harmonic vibrations overstressing timing chain components in some 5.7L applications, currently being addressed by a recall/TSB program)

...it is a very simple and reliable system these days



Yep. Sounds very simple and reliable. Especially for someone out of warranty.

 

[threeputtpar]

I agree that AFM implemented in the GM 3.9l (and the 5.3l) in the Impala is not their best work. My SIL has an 08 and if she stays in town it uses very little oil. When she drives home to visit the family, it uses 1.5 quarts in each 150 mile direction.

That is totally unacceptable. If it wasn't for her family having money from directly working for GM in the past, there's no way she would have bought that car.

 

[4wheeldog]

That reminds me of my buddy talking about his old Ford truck........He brags that it gets 100 miles to the gallon......But then it uses a lot of gasoline, too!

 

[HangFire]

Originally Posted By: lexus114
that afm stuff didnt work in the 80s either. so why would they even consider it now? that is a bad idea no matter how much electronics have improved.


Cylinder deactivation can, and does, work great... if the valves are floated. If they continue moving in 4-stroke configuration, you get suction on (what would be) the power stroke and thus oil consumption.

 

[440Magnum]

Originally Posted By: HangFire
Originally Posted By: lexus114
that afm stuff didnt work in the 80s either. so why would they even consider it now? that is a bad idea no matter how much electronics have improved.


Cylinder deactivation can, and does, work great... if the valves are floated. If they continue moving in 4-stroke configuration, you get suction on (what would be) the power stroke and thus oil consumption.


Keeping the valves moving doesn't even save fuel, because you're dragging dead cylinders along with huge pumping losses. MDS/AFM/etc. all work by deliberately letting lifters collapse so that the valves stay closed all the time.

There's a misunderstanding that its the electronics that are better than in the 80s. That's true, but that's not why the modern systems work. The modern systems work because they use very small low-power electrical systems (a small oil control solenoid valves) and let high-pressure oil do the actual activation/deactivation. The 80s systems used big solenoids and big wiring harnesses to directly manipulate the engine hardware, and that's why it didn't work reliably.

 

[tony1679]

Originally Posted By: HangFire
Cylinder deactivation can, and does, work great... if the valves are floated. If they continue moving in 4-stroke configuration, you get suction on (what would be) the power stroke and thus oil consumption.



If by "floated" you mean keeping the valves closed/separated from the rest of the valvetrain, then yes, that is exactly what GM's AFM and Chrysler's MDS does. Still both are plagued with TSBs, and at least GMs are drinking oil (I can't speak for Chrysler).

 

[Kuato]

Originally Posted By: tony1679
I just wanted to share my personal experience with this technology. For those that don't know what this is, it's GM's cylinder deactivation system for "improving fuel economy."

I bought the Impala in my sig 1 year ago with 75k miles. The first month, I noticed a significant oil loss, and I knew it wasn't leaking. During 9k miles of using Synpower 5w30 (used since the first day I bought it) it consistently "used" a full quart every 750 miles. I changed the oil every 3k for this reason. That's 3 quarts added in a 3k interval, and a quart low when it was changed. Also, I averaged 23 mpg consistently, determined both by the computer and on paper (miles/gallons).

So after reading multiple forums I realized the oil consumption is common. GM officially states 1 quart every 1,000 miles is "acceptable" and beyond that they will perform consumption tests and correct problems. Their corrections consist of a "baffle to stop oil splash" (that doesn't work) and clean or replace piston rings (which also doesn't work).

I didn't want to play games wih GM or the stealership (especially considering I was no longer under warranty) so I took matters into my own hands. I bought a handheld tuner (Superchips Cortex). Most tuners have an option to disable AFM.

From day 1 on the tune to today (97k), IT HASN'T LOST A SINGLE DROP. The icing on the cake is my fuel economy is actually slightly BETTER! I now average 23.5-24 consistently.

Based on this evidence, my opinion of DOD/AFM is obvious (and stated In my sig). I hope this gives some insight to potential/current GM owners, and I would like to hear a few thoughts on this.


Well done. I've always had misgivings about this system, regardless of manufacturer. It may work fine for the government tests when new, but down the road, as you and others have demonstrated, bad things happen. All for the sake of CAFE and in your situation it was actually a detriment to mpg.



Originally Posted By: threeputtpar
I agree that AFM implemented in the GM 3.9l (and the 5.3l) in the Impala is not their best work. My SIL has an 08 and if she stays in town it uses very little oil. When she drives home to visit the family, it uses 1.5 quarts in each 150 mile direction.

That is totally unacceptable. If it wasn't for her family having money from directly working for GM in the past, there's no way she would have bought that car.


Holy moly threeputtpar, 1.5 quarts in a 150 mile trip? I'd be disconnecting that system asap.

 

[MolaKule]

Originally Posted By: 440Magnum
I think there's something more going on here. GM AFM works almost identically to Chrysler MDS. While MDS has had some issues (harmonic vibrations overstressing timing chain components in some 5.7L applications, currently being addressed by a recall/TSB program), I don't see many reports of it causing oil consumption. The deactivated cylinders just repeatedly compress the same charge of air over and over, there's little reason to expect increased oil consumption unless its something else going on with the oil control ring package because of the lack of combustion heat, or a change in ring motion in the ring slots.

I'd experiment with oil brands, particularly using oils that resist gumming and deposit formation with top grade base-stocks- something like Pennzoil Ultra Platinum or M1, or a boutique oil. Deactivate AFM it if you want, but overall AFM/MDS whatever you want to call it is a very simple and reliable system these days, totally different from the Cadillac V8-6-4 implementation of the 1980s- any comparison to that system is spurious because the design has nothing in common.



Me too.

We have a 2008 TrailBlazer with the 5.3L V8 and I have used every oil in the industry, including mine (since it is one of my test mules), and have had zilch oil consumption since new.

 

[tony1679]

Originally Posted By: MolaKule
Me too.

We have a 2008 TrailBlazer with the 5.3L V8 and I have used every oil in the industry, including mine (since it is one of my test mules), and have had zilch oil consumption since new.


So are you saying your 5.3 has AFM but is not having issues? Congrats if that is the case. But if you think I'm wrong, you're mistaken. The only variable that changed was the AFM being disabled. Same oil, same filter, same everything.