LS Engine Tech – Active Fuel Management (AFM)

The purpose of Active Fuel Management (AFM) is to improve gas mileage. It is also known as Displacement on Demand (DOD) or cylinder deactivation.

**The table below shows the engines that were originally equipped with AFM.**

How is it identified?

The AFM system can be identified by its components.

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.)

Engine Block - All Gen. 4 blocks have AFM towers and oil passages cast in. However, they are only functional on engines that used AFM.

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

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

How does it work?

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, 4 cylinders provide no power. The engine is running on only 4 cylinders.**

The AFM cylinders are opposite one another in the firing order. In 4 cylinder mode, they act like air springs. This allows for smooth operation.

When 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 8 cylinders are now powering the engine.**

How does it affect performance?

AFM is good for gas mileage. AFM engines are 5-7% more fuel efficient. However, AFM lifters have a history of failing. Oil consumption has also been a problem. This is bad for performance.

When upgrading the engine, we recommend you Disable or Delete the AFM System.