kcops

I'm not a mechanic - so I assume GM experts did their homework and this is surely a non-long term issue. Hopefully the climate control folks did not get their way to 'this is how it must be done'. But any thoughts on impact to cylinder degrading differently if v4 is used around 50% of the time? I assume anyone doing a long trip would be running on V4, and also going around town at speed limits. Just wondering. I did see the note from GM about this as non-issue but wondering what the experts in this forum can share as well. I fully understand that one can run 100% of the time in Track mode and V8, but this is not the question. I assume a lot of folks would not drive in track mode 100% of the time. Cheers.

Vetteman Jack

That is a good question. I would hope that the engineers that designed the AFM system took that into account, but I may never know as I installed a Range AFM Eliminator to keep the car from going into 4-cylinder mode.

RKCRLR

There isn't any evidence that LT engines have long term detrimental effects from AFM.
The cylinders that are shut down due to AFM have pressurized exhaust in them (the exhaust valve doesn't open trapping the exhaust from the ignition in it). So the cylinders are seeing operating conditions similar to what they would normally see.
AFM is only active during lightly loaded conditions. A small application of throttle deactivates AFM. On a long trip the AFM is only active for 10 minutes straight and then returns to normal operation for 1 minute (or a cycle something like that).

Red Mist Rulz

There are multiple threads about this. Here's a current one:

https://www.corvetteforum.com/forums...sue-on-c8.html

Some people are convinced AFM is the devil incarnate, and your engine is bound to self destruct if you let it operate. They tend to blame any engine failure on AFM, in the total absence of any evidence supporting that. There WERE some reliability issues in the first generation of this technology, and the same people will point to failures from 20 years ago as proof the system is flawed.

GM uses this system in small block V8s across their entire line. There are literally millions of engines in use with this technology, and billions of miles on those engines. If there were major problems with it, there would be dozens of class action lawsuits, and GM car forums would have so many complaints about it there wouldn't be room to post anything else. GM sold more than 150,000 C7s with this system, and engine failures of ANY sort are rare.

Red Mist Rulz

If you installed the range device in a C8 it doesn't nothing at all.

Andybump

The Service Manual lists several conditions that inhibit V4 mode. Among them are time limits. It looks like after a period of time in V4, it transitions to V8 mode. And, once there, it looks like it must spend a minimum time in V8 mode before it can return to V4 mode. So, it really does not spend a long, uninterrupted period in V4 mode. I did not see what those times - although I think I have seen them.

As for the reason - its not stated. But it may have something to do heat. The deactivated cylinders are not firing, so the they probably tend to cool more than the ones that are firing. Switching back to V8 mode would reduce that effect.

Found the times- 10 minutes V4 mode, 1 minute V8 mode.

Chemdawg99

I have a 2009 Avalanche with AFM. Never had a problem. Ever.

Had 2016 and 2019 C7s with AFM. No issues related or relatable to AFM with either.

Member posts that are critical of AFM usually fall into at least one if not both of the categories listed below:

1. They are incredulous that a V8-powered vehicle should operate as a V4 under any circumstances.

2. The spotlight fallacy that any car with AFM is a ticking time bomb ready to grenade the engine.

Chemdawg99

Jack has a C7, not a C8.

Andybump

Here are the times - 10 minutes V4 mode, 1 minute V8 mode.

Red Mist Rulz

Since this is the C8 forum, that wasn't clear.

Also worth noting in case another member thought they should buy one to use on their C8.

Chemdawg99

Just clarifying Jack’s post in case he fails to see your post and to add context.

peter pan

I was an unlucky guy with 2015 Silverado that had a lifter issue, GM fixed under warranty and I used the range technology device after that. My 2022 Denali has that chip deleted so always in V8 mode, also how I drive my C8.

Red Mist Rulz

But even cars without AFM can have lifter issues. I remember my dad's Dodge, years ago, had a bad lifter, and no one had even thought of cylinder deactivation then.

But a bad lifter on a car equipped with AFM? Must be because of AFM, right?

MitchAlsup

An alternate PoV::


But, I can't claim that particular engine failed due to AFM, just that AFM failed on that (under cared for) engine.

Fast Dawg

There was a class action lawsuit that got filed by C7 owners on this feature. It got thrown out of court because the plaintiffs could not prove their case or refute GM’s answers to their interrogatories. That tells me everything that I need to know about it - it’s not an issue.

jimmyb

If I remember correctly, on the C7 the AFM didn't get along with the 8 speed automatic, introduced in 2015 model year. It was a transmission issue more than an AFM issue. I never heard of issues with the AFM and the 6 speed automatic (2014 only) or the 7 speed manual.
Anyone remember this?

Fast Dawg

The class action lawsuit was about it destroying the engine. I’ve read a lot of complaints about the C7 A8 transmission but I have never seen it associated with the AFM system.

jimmyb

^^^
I'll research it. There was something weird about the torque converter and the AFM interface (on the 8 speed auto) if memory serves.
FWIW, I don't know the answer to the OP's question, but I do know that the AFM operation on the C8 (I have a 2021 HTC) is totally invisible. The only way I know it's gone to V4 (or back to V8) is the light on the dash. I can't feel it or hear it when it cycles. On my C7 (2014 convertible with 7 speed MANUAL), AFM would engage only when you were in "Eco" mode. I tried it once on a trip (in Eco mode) and I could feel a slight shudder when it went to V4 (or back to V8).

Foosh

Your experiences in both C7 and C8 are identical to mine. I had the same symptoms w/ AFM on my 7MT C7, but it's completely invisible to me in the C8, except for the DIC lamp.

kcops

Thanks all for feedback. No complaints about the system itself - as mentioned above it is virtually transparent. At 35MPH when driving around town, or at 70MHP at highway I don't mind sipping on gas. I know some folks see a major difference and prefer to be on V8 all the time - and this is not an issue - just preference. The car is awesome in every other way. I sent it to the beauty shop this week - getting PPF and ceramic coating. They had a blue Callaway on the shop with carbon accents - so cool.