(Image/Summit Racing)

Active Fuel Management (AFM) is a trademarked General Motors technology that improves gas mileage by shutting down half of the cylinders under light-load conditions to reduce fuel consumption. It is also known as Displacement on Demand (DoD) or cylinder deactivation.

How Does AFM Affect Performance?

AFM is good for gas mileage and can be 5-7 percent more fuel-efficient under certain conditions.

So Why Turn it Off?

There are a few reasons:

  1. Many people find the four-cylinder sound annoying if their vehicle is equipped with a louder aftermarket exhaust.
  2. Some drivers want V8 power under their foot at all times.
  3. AFM lifters have a history of failing and oil consumption can be a problem.

How to Delete or Disable AFM on GM/Chevy Engines

There are two ways to disable or delete Active Fuel Management on your GM or Chevy Gen IV LS or LS-based Vortec engine—one is to install an AFM Disabler, and the second is to install an AFM Delete Kit. Here’s what you need to know:

1. Install an AFM Delete Kit

An AFM Delete Kit is recommended when an AFM lifter fails or when doing performance upgrades. It replaces the AFM components with standard parts.

When installing an AFM delete kit:

  • You MUST upgrade to a non-AFM camshaft because the cam lobes in the four AFM cylinders are ground differently. The engine will have 25 less pounds of compression in those four cylinders which can result in a misfire code.
  • You will need to turn off the AFM system using a computer programmer or custom tuning.
  • It’s a little more work, but it’s recommended that you plug the pressure relief valve in the oil pan.
  • It is also recommended that you switch to a standard-volume oil pump.

2. Install an AFM Disabler

An AFM Disabler is an electronic device that plugs into the OBD-II port, under the dashboard. It prevents the computer from switching over to four-cylinder mode. It’s a simple and effective way to turn off the AFM system and provides the added bonus of improving exhaust sound.

NOTE: A disabler device should ONLY be used if the valvetrain is in good working order.

Engines with AFM use a high-volume oil pump. When you eliminate the AFM system, the extra oil is no longer needed. Excess oil will be pushed out of the pressure relief valve into the oil pan. This will spray oil on the bottom of the cylinder walls which can cause oil burning, especially in high-rpm engines.

Which Option is Best—a Disabler or Delete Kit?

As long as a lifter hasn’t started to fail, you can get by with a less-expensive disabler as preventative maintenance. If a lifter has already started to fail, an AFM delete kit and non-AFM components are the way to go.

NOTE: If you were in a situation where you’ve installed the AFM delete kit, but don’t have access to a programmera disabler can still be a viable option. To do this, you 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.

GM/Chevy Engines Factory-Equipped with AFM

Engine DisplacementRPO Code

How to Identify AFM Engine Components

The AFM system can be identified by its components. Look for the following:

1. Valley Cover

The AFM cover is called the Lifter Oil Manifold Assembly (LOMA). It’s ribbed with solenoids on the underside. It also has an electrical connector on the back. (Non-AFM engines have a smooth cover.)

LS - Lifter Oil Manifold Assembly (LOMA)
(Image/Summit Racing)

2. Engine Block

All Gen IV engine blocks have AFM towers and oil passages cast in. However, they are only functional on engines that used AFM.

LS - AFM Towers
(Image/Summit Racing)

3. Lifters

AFM engines use special lifters for cylinders 1, 4, 6, and 7. They are taller and have special oil holes.

LS - AFM lifters labeled
(Image/Summit Racing)

Engines with AFM also use a special camshaft, a high-volume oil pump, and a pressure relief valve in the oil pan.

3. Oil Pressure Relief Valve

This valve is located on the oil pan rail and prevents excessive oil pressure from negatively impacting the AFM components. The original version sprayed oil on the cylinder walls and increased oil consumption. In 2010, GM added a deflector (p/n) NAL-12639759 to redirect in into the pan. This should be added to your earlier model if you experience oil consumption.

The valve itself is part number W0133-2574213. If you want to delete it entirely, it’s a M14 x 1.5 pipe plug or you could use the Improved Racing plug p/n IRP-814-M14-Kit.

How Active Fuel Management (AFM) Works

How Active Fuel Management (AFM) Works

When engine load is low:

  1. The computer sends a signal to the LOMA.
  2. The LOMA solenoids open.
  3. Oil flows to the special lifters through the AFM towers.
  4. The oil collapses the plunger inside the lifter.
  5. The collapsed lifters will not engage the pushrods and both valves remain closed.

Since no air can get in or out, four cylinders provide no power. The engine is running on only four cylinders.

The AFM cylinders are opposite of one another in the firing order. In four-cylinder mode, they act like air springs and allow for smooth operation.

As engine load increases:

  1. The computer sends a signal to the LOMA.
  2. The LOMA solenoids close.
  3. Oil bleeds off the lifters.
  4. The lifters return to normal operation.

All eight cylinders are now powering the engine.

NOTE: Some parts are not legal for use in California or other states with similar laws/regulations.

NOTE: You can find engine specs and detailed engine upgrade advice for every LS and LS-based Vortec truck engine in one place: The Definitive Guide to LS Engine Specs and LS Engine Upgrades.

Author: Brian Nutter

After a stint in the U.S. Air Force, Brian Nutter studied at the Houston, TX-based School of Automotive Machinists in 1997. The early part of his automotive career included working for engine builders Scott Shafiroff and C.J. Batten, followed by several years developing performance pistons at Wiseco Piston Co. Today, Brian develops performance parts for Summit Racing Equipment and is a regular OnAllCylinders contributor. For fun, he runs his 427-powered C5 Z06 in ECTA land-speed racing, at OPTIMA® street car events, and at a mix of autocross, drag racing, and track days.