I’ve read some things regarding the AFM (V8/V4) on the GM engines and that it’s detrimental to the engine. I need some knowledge and opinions on this subject. Is this valid and is a device such as the one made by Range Technology a good and / or safe solution?
Thanks
Submitted by: James Edwards
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The AFM system consists of both mechanical parts and an electronic control system. The Range device simply bypasses the control system, while all the mechanical complexity is still there. Issues such as those noted can likely be dealt with via that Range device, but the system will still be subject to mechanical failures which are not uncommon.
Each cylinder involved has unique lifters, one for intake and one for exhaust, that can effectively be disabled via oil pressure so that the lifter essentially "collapses" and the valves don't open. Coupled with disabling fuel injection and spark, that renders those cylinders inactive during AFM operation. There is a unique valley cover "manifold" which controls that oil pressure via electrical solenoids. It's not unusual for a solenoid or one of those unique lifters to fail, causing physical damage (don't ask me how I know). The Range device won't prevent that, but one of the main causes of failure is not keeping fresh clean oil in the engine, which can be addressed.
The issue is significant enough that there are aftermarket kits that replace those unique lifters and lifter guides as well as the manifold, which along with reprogramming the electronics totally eliminates the AFM system.
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Bob Neff on
2/3/2024 2:21:37 PM
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Short answer: YES and YES!
I have a 2017 Grand Sport Z07 with an A8 automatic which unfortunately came with AFM (manuals do not). I track with it, and the exhaust valve actuators upstream of the mufflers melted down (because they have metal valve shafts mated to nylon gears!) 6 out of the first 6 track days I ran with it! And when they melted down, the system freaked out going from 4 to 8 cylinders in any mode, even on a track. Long, sordid, story, but GM replaced them 6 times under warranty (track days, a.k.a. "high performance driver education" events, are covered!), including the entire exhaust system cat back twice, the second one sent out to have the entire thing ceramic coated, which is the secret GM motorsports "fix". Did not work because the design flaw is in the actuators (same as used for the active exhaust, but in a much cooler location - bean counters strike again!). After the last, GM declared the issue permanently fixed and sated they would not repair again. They offered me $1000 compensation, which I told them to shove (after having multiple track days ruined at great cost, and 89 days total out of service!).
So, my choice was to sell it, or eat and replace the entire exhaust without the valves. I installed a Z06 Corsa system (retaining active exhaust), and a Range OBDII module to defeat the AFM system. Still had issues. So I installed new actuators, plugged into the harness and hung but not installed on the exhaust (no valves to hook up to). Still had a check engine light and codes. So I installed AWE AFT valve simulator plates, finally resolving the issue permanetly. Altogether, 3 season of issues and about $3000 (parts + labor - I'm too old for this s***)!
Bottom line: I believe that cylinder deactivation systems are bad for engines, regardless if they are working properly. They cause uneven engine temperature and wear. As such, I would highly recommend a Range OBDII module - just remember to pull it if you ever take your car into a dealer. But if you track with a C7 (or C8 I assume) with AFM, you will probably also need to remove the exhaust hardware as well (perhaps not needing to replace the entire exhaust?).
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James Anderson on
2/2/2024 1:36:48 PM
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I won’t say my response is an especially educated one but I didn’t buy a Corvette for Economy. I never liked the sluggish feel of mine when it was in 4 cyl mode and the switch between modes was always noticeable. I have been using the Range device in my 2019 GS for almost 2 years and had zero issues. Keep in mind that if you use the Range and park the car for extended periods (week or more) you’ll want to unplug it since it does draw on the battery even when the car isn’t running. I have been much happier using the Range device.
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Randall Williams on
2/2/2024 5:33:45 AM
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