Active Fuel Management (AFM) is a trademarked name by General Motors. The technology was designed to improve gas mileage by shutting down at least half of the cylinders under light-load conditions to improve fuel economy. AFM is also referred to as cylinder deactivation or Displacement on Demand (DoD).
GM active fuel management is mainly reserved for larger GM vehicles with V-8 or V-6 engines. For V-6 engines, AFM temporarily turns the car into an inline V-3 engine, while V-8 engines are briefly reduced to V-4 performance.
How Does Active Fuel Management System Work?
The concept behind AFM is that high-powered engines are very inefficient whenever high-demand power is not necessary. Experts estimate that most V8 and V6 engines only require about 25% of the engine’s total power for everyday driving. Instead of installing a more efficient and smaller engine that might tow capacity and acceleration, the AFM technology deactivates unnecessary cylinders when needed to improve efficiency.
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Cylinder deactivation begins by turning off the intake and exhaust valves. The process is done via a solenoid control valve assembly, signaled via pressurized oil to activate and deactivate hydraulic roller lifters. The filters are the ones that physically close and open the intake and exhaust valves. When both valves are closed, any exhaust gas that remains in the cylinders expands in one cylinder as it decompresses in the other one. The compression helps in maintaining power in low-demand situations. When more power is needed, the exhaust valve reopens to discharge the old exhaust gas to allow in a new cycle.
The AFM system requires considerable electronic control because of the extreme precision needed to create a seamless operation. Several factors, including engine emission controls, advancements in-vehicle system computing power, and Electronic Throttle Control, have contributed to the successful assimilation of the AFM technology in modern vehicles.
What Are the Drawbacks of Using the AFM System?
Although the AFM system helps in improving fuel economy, there are some problems associated with it. Here are some of the drawbacks of using the Active Fuel Management system:
- Oil might get past the piston and enter the combustion chamber. When oil gets burnt out or accumulated in the combustion chamber, it might create a significant problem in the future.
- Most car owners do not enjoy the feel when half of the cylinders are turned off or when their cars are being transformed from full on to half off.
- Faulty lifters: The AFM system constantly keeps the lifters working by deactivating and activating them frequently. The lifters may require replacement quickly.
How to Disable AFM
The minor drawbacks discussed above may make you want to disable or turn off active fuel management. There are two ways to delete or disable active fuel management on your vehicle. One of them is installing an AFM delete kit, and the other is installing an AFM disabler.
Here is what you should know about the process:
Install an AFM Delete Kit
An AFM Delete Kit is highly recommended when performing upgrades or when an AFM filter fails. The AFM delete kit replaces the AFM components with standard parts.
During the installation of the AFM delete kit:
- Upgrade to a non-AFM camshaft because the cam lobes in the four AFM cylinders are ground differently. Your engine will have at least 25 fewer pounds of compression in the four cylinders, which might result in a misfire code.
- Turn off the AFM system using custom tuning or a computer programmer.
- Plugging the pressure relief valve in the oil pan is recommended.
- Switching to a standard-volume oil pump is recommended.
How to Disable AFM Without a Tune
You can disable the AFM without the tuning using the following methods:
Use an AFM Disabler
An AFM Disabler is a functional electronic device that plugs into the OBD-II port under the dashboard. The device prevents your vehicle’s computer from switching over to four-cylinder mode. The technique is a simple and effective way of turning off the Active Fuel Management System and improving exhaust sound.
You should only use an AFM Disabler if the valve train is in excellent working condition. It’s worth noting that engines with an AFM system use a high-volume oil pump; therefore, the excess oil is no longer required when you remove the AFM system. The extra oil will be pushed out of the pressure relief valve into the oil pan. This sprays oil on the bottom of the cylinder walls and can cause oil burning, especially in engines with a high RPM.
If you’ve installed the AFM delete kit but cannot access an AFM deleter programmer, a disabler may still be a viable option. To use the option, you will need to leave the AFM solenoid pack connected to ensure no codes are thrown. You can reuse the original valley cover or use a non-AFM valley cover, leave the harness connected, and tuck the solenoid pack away.
Disconnect the Brake Booster Vacuum Sensor
You can disable the AFM by disconnecting the brake booster vacuum sensor. However, this method does not work for all vehicles. Although it’s not a fool-proof plan, it will get the AFM disabled. You might need to scan the car sometimes to check if your car is having issues after disabling AFM.
Will Disabling AFM Save Lifters?
Disabling AFM will save the lifters. If a lifter hasn’t started failing, you can use a less expensive disabler as preventative maintenance. However, if a filter has started failing, non-AFM components and an AFM delete kit may be the way to go.
How to Prevent AFM Lifter Failure
Your AFM lifter might still fail even if it doesn’t have a problem. You can’t prevent the lifters from failing forever; however, you can ensure they have a prolonged life by doing the following:
Ensure Quality Oil
Poor quality oil can destroy your lifters. If you want yours to remain in good shape, ensure the oil you’re using is of excellent quality.
Have Adequate Oil Supply
Metallic structures require liquid elements for them to perform smoothly and efficiently. If you want to prevent lifter failure, you will have to use enough oil over the sliding surface. Having enough oil will reduce the chances of early failure.
How to Tell if a Vehicle Has Active Fuel Management
You can mainly identify the AFM system by its components. You can tell if your vehicle has an Active Fuel Management System by looking at the following:
Valley Cover
The AFM cover is known as the Lifter Oil Manifold Assembly (LOMA). The cover is ridged with solenoids on the underside and also contains an electrical connector on the back. The non-AFM engines have a smooth cover.
Lifters
Engines with AFM use distinctive lifters for cylinders 1, 4, 6, and 7. Additionally, they have unique oil holes and are taller.
Engine Block
Gen.4 blocks have AFM towers and oil passages cast in. However, these are only functional on engines that use AFM.
Does Tow Mode Disable AFM?
Tow mode will not stop the AFM from engaging; however, downshifting to “3” might prevent it. Towing will most likely add heat to the transmission and engine. You should add a transmission cooler if you tow heavy stuff often.
Disabling the AFM is a straightforward process if you understand what needs to be done. However, if things become complicated during any stage of the disabling process, you should consult an expert or someone who’s done it before.