C8 AFM Disable?
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
All this AFM the sky is falling and we need to "fix" this makes me laugh. The AFM has oil control solenoids, so does your variable cam timing, how many are trying to "fix" that? Let them get you great gas milage when you are steady state cruising, as soon as you're not, it's a V8.
Safety Car
Joined: Nov 2005
Posts: 4,381
Likes: 939
From: Huntsville Alabama
All this AFM the sky is falling and we need to "fix" this makes me laugh. The AFM has oil control solenoids, so does your variable cam timing, how many are trying to "fix" that? Let them get you great gas milage when you are steady state cruising, as soon as you're not, it's a V8.
If a AFM lifter fails the motor starts to eat itself instantly.
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
All this AFM the sky is falling and we need to "fix" this makes me laugh. The AFM has oil control solenoids, so does your variable cam timing, how many are trying to "fix" that? Let them get you great gas milage when you are steady state cruising, as soon as you're not, it's a V8.
from AI...
Low Failure Rate:
While some sources suggest a failure rate around 5%, others estimate it to be closer to 1% or less, particularly for newer vehicles.
- Significant Impact:
Even with a low failure rate, the sheer number of GM vehicles with AFM means that a substantial number of vehicles could potentially experience AFM-related issues. - Factors Contributing to Failure:
Several factors can contribute to AFM failures, including long oil change intervals, bad batches of lifters (e.g., some 2021 models), and potential issues with the Valve Lifter Oil Manifold (VLOM) that controls AFM activation. - Cost of Repair:
Lifter failures, a common AFM-related issue, can be expensive to repair, potentially ranging from $3,000 to $11,000.
As for the great gas mileage thing I'm betting in a 1000 miles of using it verses not using it you couldn't calculate a "real" difference if it was truly a blind accurate test...and certainly never pays for itself no more often than most c8 gets driven especially when you add in the minimal times AFM is actually in use....
imo of course....I'm more likely to laugh at people think all that extra junk that isn't really needed in your engine is a good thing for an already too complex engine...
alas different strokes...
Last edited by hawkgfr; Jun 12, 2025 at 04:51 PM.
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
As for the great gas mileage thing I'm betting in a 1000 miles of using it verses not using it you couldn't calculate a "real" difference if it was truly a blind accurate test...and certainly never pays for itself no more often than most c8 gets driven especially when you add in the minimal times AFM is actually in use....
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
Please show all the AFM failures in the LT2 engine. Not some 20 year old news about a 5.3 or some other outdated news. The naysayers are acting as if there has only been one design and it has never been updated, improved, or revised. It has been stone reliable in the LT2 and clinging to the past just shows a lack of understanding.
Racer
Joined: Oct 2022
Posts: 372
Likes: 176
From: Montgomery, AL
I really find it hard to believe hat GM designed a system that doesn't circulate the oil in those lifters. It's the same system used in the C7, and there were many thousands of C7 manuals that never saw AFM mode. Pretty sure the only time the lifters don't get pressurized oil is when the car is in V4 mode. In V8 mode they work like any other hydraulic lifter.
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Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
Please show all the AFM failures in the LT2 engine. Not some 20 year old news about a 5.3 or some other outdated news. The naysayers are acting as if there has only been one design and it has never been updated, improved, or revised. It has been stone reliable in the LT2 and clinging to the past just shows a lack of understanding.
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Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
from AI...
Low Failure Rate:
While some sources suggest a failure rate around 5%, others estimate it to be closer to 1% or less, particularly for newer vehicles.
As for the great gas mileage thing I'm betting in a 1000 miles of using it verses not using it you couldn't calculate a "real" difference if it was truly a blind accurate test...and certainly never pays for itself no more often than most c8 gets driven especially when you add in the minimal times AFM is actually in use....
imo of course....I'm more likely to laugh at people think all that extra junk that isn't really needed in your engine is a good thing for an already too complex engine...
alas different strokes...
Low Failure Rate:
While some sources suggest a failure rate around 5%, others estimate it to be closer to 1% or less, particularly for newer vehicles.
- Significant Impact:
Even with a low failure rate, the sheer number of GM vehicles with AFM means that a substantial number of vehicles could potentially experience AFM-related issues. - Factors Contributing to Failure:
Several factors can contribute to AFM failures, including long oil change intervals, bad batches of lifters (e.g., some 2021 models), and potential issues with the Valve Lifter Oil Manifold (VLOM) that controls AFM activation. - Cost of Repair:
Lifter failures, a common AFM-related issue, can be expensive to repair, potentially ranging from $3,000 to $11,000.
As for the great gas mileage thing I'm betting in a 1000 miles of using it verses not using it you couldn't calculate a "real" difference if it was truly a blind accurate test...and certainly never pays for itself no more often than most c8 gets driven especially when you add in the minimal times AFM is actually in use....
imo of course....I'm more likely to laugh at people think all that extra junk that isn't really needed in your engine is a good thing for an already too complex engine...
alas different strokes...
Someone over on MECF just did a comparison with and without the Carbyte. An admittedly limited test, but showed about 1 mpg difference in suburban driving. Not huge, but not insignificant. It also showed (and I've noticed the same), in Tour mode the V4 light is on nearly all the time in suburban type surface street driving. The AFM use is anything but "minimal" in Tour mode. On the highway it's on 80 to 90% of the time.
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
Hence the winky emoji....
But if we're being fair...that AI is probably better than the plethora of information you provided when you mocked those who thinks AFM sucks...what they think is not affecting your sky now is it?
Rhetorical I know the answer....Last edited by hawkgfr; Jun 13, 2025 at 12:48 AM.
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
You're not thinking clearly, if it made no difference at all, why would GM make the car more complex and STILL have the same problem with CAFE ratings? You're simply guessing that there is zero savings and no facts to support your argument and there is no logic to back it up either.
Go ahead see if you can calculate an actual real life difference....(no cheating now)
Team Owner
Joined: Apr 2008
Posts: 22,581
Likes: 1,696
From: South Carolina
There are what, 250,000 C8s on the road? Each one with 8 AFM lifters? 2 million of the things? A 1% failure rate would be 20,000 failed lifters. The forum would have thousands upon thousands of posts of bad engines. And there are 10s of millions of GM engines with AFM lifters. if they failed at anywhere near 1% there would be riots at dealerships. The real failure rate is probably something like 0.001 percent.
Someone over on MECF just did a comparison with and without the Carbyte. An admittedly limited test, but showed about 1 mpg difference in suburban driving. Not huge, but not insignificant. It also showed (and I've noticed the same), in Tour mode the V4 light is on nearly all the time in suburban type surface street driving. The AFM use is anything but "minimal" in Tour mode. On the highway it's on 80 to 90% of the time.
Someone over on MECF just did a comparison with and without the Carbyte. An admittedly limited test, but showed about 1 mpg difference in suburban driving. Not huge, but not insignificant. It also showed (and I've noticed the same), in Tour mode the V4 light is on nearly all the time in suburban type surface street driving. The AFM use is anything but "minimal" in Tour mode. On the highway it's on 80 to 90% of the time.
that's some powerful empirical evidence....Similar to the transmission data we have....
For real though...
I do agree the problem is minimal with the c8 on the afm but its not that great on other GM engines.......but I'm sticking you can't verify a real fuel savings and cost add justification on any of them...but its ok...you like grape kool aide its all good...
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 35,020
Likes: 12,402
From: NE South Carolina
You're not thinking clearly, if it made no difference at all, why would GM make the car more complex and STILL have the same problem with CAFE ratings? You're simply guessing that there is zero savings and no facts to support your argument and there is no logic to back it up either.
The ICE is very inefficient. Only about 20% of the energy in gasoline gets to the rear wheels. The other 80% goes into the coolant thru Rad to air, directly to air out the exhaust and ~10% is wasted idling. In V4 that is half the cylinder wall and cylinder head area that does not have to dissipate the ~2000F combustion heat into coolant!
It's even worse as "on average" of the ~20% that does get to the rear wheels ~1/4 goes to heat when braking! Where my E-Ray capturing some of that otherwise braking emery to change the battery!
Also some of that ~10% wasted idling energy can be saved with start/stop. I never shut it off in my E-Ray and we didn't in my wife's recent BMW X5 SUVs. And love the starter motor will fail subjective reason for shutting it off! The wife's last BMWs didn't use the starter after Stop/Start! They used a form of what was called the Cauffman Starter used in WWII airplanes! They shut the motor off right after a combustion event and use the captured combustion pressure to turn the engine over to start! Sound complex-NOT! For all 4 of the V4 cylinders than shut they capture combustion pressure so the shut off cylinder acts like an air spring when not firing!
BTW, this is a video by Jason Fenske (Engineering Explained) showing Stop/Start in tests got up to 8.7% better mpg!
Last edited by JerryU; Jun 13, 2025 at 07:31 AM.
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
I call out lack of sense, logic, ignorance, whatever you want to call it. I've actually seen people post "I don't want it because I BOUGHT a V8 and by God that's what I want." This statement shows a 100% lack of understanding. It ONLY works while the car is at steady state cruise with zero acceleration. The driver wouldn't know if it had an engine or if it was being towed by a Schnauzer. Yet they act as if this wheezing 4 cylinder just won't snap out of it as traffic leaves them in the dust as they desperately attempt to accelerate. It is NOT the case in the remotest way. My sky is just fine, I'm just trying to ask the uninformed to open their minds a bit and learn.
Race Director
Joined: Aug 2019
Posts: 12,351
Likes: 14,185
From: Central Illinois
And please explain the failure mode that causes engine damage. I have yet to see anyone explain the logic of how a failure here causes damage elsewhere. Exactly what fails in the mechanism, and by what sequence of events does that destroy the engine? I see a lot of rumor, urban legend and panic, but no actual data.
Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,528
For real though...
I do agree the problem is minimal with the c8 on the afm but its not that great on other GM engines.......but I'm sticking you can't verify a real fuel savings and cost add justification on any of them...but its ok...you like grape kool aide its all good...
[/QUOTE]This. GM didn't spend tens or hundreds of millions developing the technology, and further millions buying millions of complex parts, because it doesn't work. How big a gain is going to be dependent on a lot of factors, many related to the driver, but especially on the highway the benefits are real.
Safety Car
Joined: Nov 2005
Posts: 4,381
Likes: 939
From: Huntsville Alabama
Some of you act like other cant feel it or want it. Some of us like gadgets and to play with the cars. I personally feel V4 swapping, when in auto and around town, and I would rather not. I believe it gets better fuel (how much probably minimal as other are saying) but dont really matter the C8 is the best car I have MPG wise anyway.
its a toy, it makes v4 go away for people who don't like it, who dont like the lifters for right or wrong reasons, or who like to test new gadgets.
its a toy, it makes v4 go away for people who don't like it, who dont like the lifters for right or wrong reasons, or who like to test new gadgets.
Drifting
Joined: Aug 2022
Posts: 1,904
Likes: 791
From: Stamford, CT
I don't think AFM is a big issue as far as failures on the LT2 go. I also don't believe that it saves gas in any meaningful way, I see negligible difference so far with carbyte on. ~1 mpg, maybe. What I hate is the clunkiness of AFM. I don't buy all the 'Tadge' b.s. of slipping the clutch and what not. Mine sucks. If the DCT is shifting concurrently with AFM activating to V4, the whole drivetrain makes it known to me. In some cases I feel it frst and then I see the V4 light come on so I know I am not imagining it.
Race Director
Joined: Aug 2016
Posts: 12,812
Likes: 10,229
From: Garden Valley CA
And please explain the failure mode that causes engine damage. I have yet to see anyone explain the logic of how a failure here causes damage elsewhere. Exactly what fails in the mechanism, and by what sequence of events does that destroy the engine? I see a lot of rumor, urban legend and panic, but no actual data.
People that have lifter failures often blame it on AFM without actually knowing if the failure was caused by the AFM mechanism failure. The AFM lifters seem to be more sensitive to oil contamination and low oil pressure at the lifter. Perhaps that is one of the reasons you rarely see AFM failures in LT engines. Corvette owners tend to over maintain their engines whereas many truck owners just drive and change the oil when they feel like it.