GM's AFM, or Active Fuel Management, technology has been wreaking havoc on lifters for nearly two decades. In 2019, they expanded upon this technology making significant changes to its functionality with the release of DFM, or Dynamic Fuel Management. This technology is also frequently marketed as Displacement on Demand, or DoD.
The main difference between the two is that AFM simply deactivates half of an engines cylinders, going from V8 to V4 mode, whereas DFM has 17 different firing patterns and can shut down up to 6 cylinders in V8 engines, in any random combination.
Both AFM and DFM do the same thing: deactivate various cylinders to improve fuel economy. But, they do so in very different ways. In this article I'm going to discuss the technology behind AFM and DFM and how they differ, and discuss the lifter failure problems that each of them causes.
How AFM Works
Active fuel management can only deactivate four specific cylinders: 1 and 7 on the left bank, and 4 and 6 on the right bank. A combination of signals from the engine causes the ECM to activate AFM and shut these cylinders off. In V6 engines cylinders 3 and 6 are deactivated, also turning it into V4 mode.
This process takes place using oil pressure, via a combination of complex oil passages, solenoids, and special lifters. Knock yourself out if you want to dig into the technical specifics of how AFM works.
From a hardware standpoint, there are oil control valves in the lifter oil manifold assembly (LOMA) for the specific four cylinders that deactivate. These four cylinders also use specific AFM-lifters that are slightly different from the lifters in the other four cylinders.
How DFM Works
Dynamic fuel management is the more advanced successor to active fuel management. The technology behind it was actually developed by a third-party company, Tula Technology, specifically for GM to improve upon AFM.
For DFM engines, the oil control valves are integrated into the engine block and all eight cylinders have a control valve and have the specialized lifters. This means that any one of the 8 cylinders can be deactivated, instead of just the specific four in AFM engines.
In a test by GM, DFM was enabled more than 60% of the time compared to AFM which was activated 52% of the time.
Problems Caused by AFM & DFM
The biggest issue with active and dynamic fuel management are the problems that they cause. With both of these technologies an engine is operating with less than all its cylinders on more than 50% of the time.
Furthermore, these systems constantly activate and deactivate. DFM calculates what 'mode' the engine should be in 80 times per second, so the engine is constantly switching between modes thousands of times during a standard driving session. Over time the lifters and internal components start to wear down from the constant turning on and off - which causes stuck lifters, collapsed lifters, and other serious problems.
Here are a few problems these systems cause:
- Lifter failure (stuck lifters, collapsed lifters, etc.)
- Excessive oil consumption
- Hesitations when accelerating
- Jerking and rough shifting from the transmission
- Delayed throttle response
- Valvetrain wear and tear
- Potential engine failure
Lifter Failure & Oil Consumption
The two most common problems with AFM & DFM are lifter failure and excessive oil consumption.
Lifter failure is extremely common once vehicles start reaching the 150,000 mile mark. However, it can happen much sooner and some DFM engines have begun experiencing failure in as little as 30,000 miles. DFM vehicles are slightly more likely to experience failures compared to AFM engines since 1) the system is activated more often, and 2) every single cylinder has the hardware, compared to just half the cylinders. The bad news is that lifter failure is very common on AFM engines, and we suspect it will become even more common on DFM engines once they start to get older (DFM was first released in 2019 so it is still relatively new).
Excessive oil consumption tends to appear more quickly, affecting vehicles closer to the 60,000-80,000 mile range. In bad cases engines can use 1 quart of oil every 1,000 miles of driving. The problem with oil consumption is what can ultimately lead to engine failure. Drivers need to make sure they are always topped up on oil otherwise low levels can lead to oil starvation and more serious engine damage.
Ultimately, lifter failure on both AFM & DFM engines is a question of when, not if. It can lead to $2,000-$5,000 repair bills - but there are some affordable preventative measures you can take to save your lifters.
Prevent Problem by Disabling AFM & DFM
The easiest way to prevent a lot of the issues that these fuel management systems cause is to simply disable them. Disabling them will prevent them from deactivating cylinders, keeping your engine in V8 or V6 mode 100% of the time, which keeps your lifters lifting all the time. The problems these systems cause is because of the frequency of shutting cylinders off and turning them back on, so to mitigate issues the best thing is to keep all cylinders on all the time.
The easiest way to do this is with a disabler device, like our BOOST AFM & DFM Disabler. It simply plugs into your OBDII port and begins working in seconds, keeping your vehicle in V8/V6 mode all the time and therefore preventing the issues these systems cause.
Here are some of the benefits of our Boost AFM & DFM Disabler:
- V8/V6 mode 100% of the time
- Improves reliability and helps prevent lifter failure
- Increases performance with more throttle response and less hesitations
- Smoother shifts and overall smoother driving experience
- Plug-and-play: just unplug the device and everything returns to normal
- Decreases oil consumptions issues and premature valvetrain wear
- Lowest battery drain on the market
Our device is manufactured in the United States. There are dozens of knock-off devices available on Amazon that come directly out of China, from Chinese sellers. Our device was engineered in the US, manufactured in the US, and is sold from the US.
Furthermore, a number of the existing devices from China, and even Range's device, are known to cause issues with battery drain causing no-starts and dead batteries. We've engineered in an extremely low power mode that draws very minimal current from the battery, preventing any issues with battery drain. You can leave our device plugged in for weeks without draining your battery whereas a lot of the devices on the market will drain your battery in under a week.
