Active Fuel Management (AFM), also known as Displacement on Demand (DOD), is a technology by General Motors designed to boost fuel economy. It cleverly shuts down half of your engine’s cylinders when you’re cruising or under light load. While AFM can save you gas, many GM owners choose to disable or delete it for various reasons. If you’re considering disabling AFM on your Chevy or GM engine, especially if you’re dealing with a 2006 Trailblazer or similar model and thinking about using an OBD2 device, this guide is for you. We’ll explore the pros and cons of AFM, why you might want to disable it, and the two main methods: AFM Delete Kits and OBD2 Disablers, helping you make the best decision for your vehicle.
Understanding Active Fuel Management (AFM) and Its Impact
AFM’s primary goal is fuel efficiency. By running your V8 engine as a four-cylinder under light loads, it reduces fuel consumption. GM claims AFM can improve fuel economy by 5-7% under ideal conditions.
The Downsides of AFM: Why Disable It?
Despite the fuel-saving benefits, AFM isn’t always desirable. Here are common reasons why owners choose to disable or delete it:
- Annoying Exhaust Note: Many find the sound of a V8 switching to four cylinders, especially with aftermarket exhaust systems, to be unpleasant or unusual. The change in exhaust note can be jarring.
- Desire for Consistent V8 Power: Some drivers simply prefer to have all eight cylinders engaged at all times for consistent power delivery and a more traditional V8 driving experience. They want instant V8 power whenever they need it.
- AFM Lifter Reliability Issues: Perhaps the most significant concern is the history of AFM lifter failures. These specialized lifters are prone to problems, and their failure can lead to engine damage and increased oil consumption. This reliability concern is a major driver for AFM deletion.
Two Main Methods to Disable AFM on GM/Chevy Engines
If you’ve decided to disable AFM on your Gen IV LS or LS-based Vortec engine, you have two primary options: installing an AFM Delete Kit or using an AFM Disabler device. Let’s examine each in detail.
1. AFM Delete Kit: The Permanent Solution
An AFM Delete Kit is the more comprehensive and permanent solution. It involves physically replacing the AFM components with standard, non-AFM parts. This is often recommended when AFM lifter failure has already occurred or when you’re undertaking performance upgrades to your engine.
What’s Involved in an AFM Delete Kit Installation?
- Non-AFM Camshaft is Essential: This is a MUST. AFM camshafts have different lobe profiles for the cylinders that deactivate. Using the original AFM camshaft with a delete kit will result in lower compression in those cylinders and likely cause misfire codes.
- ECU Programming is Required: You absolutely need to disable the AFM system in your engine’s computer (ECU) after installing a delete kit. This can be done with a computer programmer or by getting a custom tune. This step is crucial to prevent error codes and ensure proper engine operation.
- Oil Pan Pressure Relief Valve Plug (Recommended): It’s advisable to plug the pressure relief valve in your oil pan. AFM engines use a high-volume oil pump, and without AFM, this valve might release excessive oil.
- Standard Volume Oil Pump (Recommended): Switching to a standard-volume oil pump is also recommended. Since the high volume is no longer needed for AFM, a standard pump is sufficient and can prevent potential issues.
2. AFM Disabler Device: The Simpler OBD2 Solution
An AFM Disabler is an electronic device that offers a simpler way to disable AFM. It plugs directly into your vehicle’s OBD2 port, usually located under the dashboard. By plugging in, it effectively tells the engine computer to never engage four-cylinder mode.
How does an OBD2 AFM Disabler work? These devices work by sending a signal through the OBD2 port that prevents the ECU from activating the AFM system. Think of it as a simple “master switch” connected via your OBD2 port to keep your engine running in V8 mode constantly. This is a quick and easy way to turn off AFM and can even improve exhaust sound by maintaining V8 operation.
Important Note: Only use an AFM disabler if your engine’s valvetrain is in good condition. If you suspect lifter issues, a delete kit is the more appropriate long-term solution.
Oil System Considerations with Disablers: Even with a disabler, your engine still has the high-volume oil pump intended for AFM. Since AFM is disabled, the excess oil will be routed through the pressure relief valve and sprayed onto the cylinder walls. While generally not a major issue for normal driving, in high-RPM or performance situations, this could contribute to oil burning over time.
AFM Disabler vs. Delete Kit: Which Option is Right for You?
The best choice depends on your situation and goals:
- AFM Disabler: Ideal as a preventative measure if your AFM system is currently functioning correctly and you want a quick, reversible, and less expensive way to disable AFM. It’s also a good option if you simply dislike the AFM sound or want consistent V8 power. For a 2006 Trailblazer owner looking for a simple solution via the OBD2 port, this could be very appealing.
- AFM Delete Kit: The recommended path if you’re experiencing AFM lifter failure, planning engine performance upgrades, or want a permanent solution to eliminate AFM and its potential long-term issues. While more involved and costly, it provides greater peace of mind, especially for long-term reliability.
Can You Use a Disabler After an AFM Delete Kit Install (Without a Programmer)?
Interestingly, yes, in a pinch. If you’ve installed an AFM delete kit but haven’t yet programmed the ECU, an AFM disabler can be used temporarily. To avoid error codes, you would need to leave the AFM solenoid pack connected electrically (even if physically removed from the valley cover) so the system thinks it’s still functioning. However, proper ECU programming is always the recommended step after an AFM delete.
Identifying AFM Components on Your GM Engine
Knowing how to identify AFM components can be helpful. Here’s what to look for:
1. Valley Cover (Lifter Oil Manifold Assembly – LOMA)
The AFM valley cover is distinctive. It’s ribbed and has solenoids on the underside. You’ll also see an electrical connector at the back. Non-AFM engines have a smooth valley cover.
2. Engine Block
All Gen IV engine blocks have AFM towers and oil passages cast into them. However, these are only functional on engines that were actually equipped with AFM.
Alt text: AFM towers visible on a Gen IV LS engine block, indicating Active Fuel Management capability.
3. AFM Lifters
AFM engines use special lifters on cylinders 1, 4, 6, and 7. These lifters are taller and have unique oil holes.
Alt text: Specialized AFM lifters for GM engines, taller with distinct oil holes for cylinder deactivation.
Additionally, AFM engines use a specific camshaft, a high-volume oil pump, and a pressure relief valve in the oil pan.
4. Oil Pressure Relief Valve
Located on the oil pan rail, this valve regulates oil pressure for the AFM system. Earlier versions could spray oil onto cylinder walls, potentially increasing oil consumption. GM later released a deflector (p/n NAL-12639759) in 2010 to redirect oil flow and mitigate this.
GM/Chevy Engines Factory-Equipped with AFM
Here’s a table of common GM engines that came with AFM from the factory:
| Engine Displacement | RPO Code |
|---|---|
| 5.3L | LY5, LC9, LH6, LMG, LS4 |
| 6.0L | L76, L77, LFA, LZ1 |
| 6.2L | L94, L99 |
How AFM Cylinder Deactivation Works
Understanding the mechanics of AFM can further clarify why disabling it might be desired.
Alt text: Diagram illustrating Active Fuel Management (AFM) process in a GM engine.
In Low Engine Load Conditions:
- The engine computer signals the LOMA (Lifter Oil Manifold Assembly).
- LOMA solenoids open.
- Oil flows through AFM towers to the special lifters.
- Oil pressure collapses the plunger inside the AFM lifters.
- Collapsed lifters prevent pushrod engagement, keeping valves closed.
With valves closed, these four cylinders become inactive, acting as air springs for smoother operation while the engine runs on four cylinders.
When Engine Load Increases:
- The computer signals the LOMA again.
- LOMA solenoids close.
- Oil pressure bleeds off the AFM lifters.
- Lifters return to normal operation.
All eight cylinders are now active, providing full engine power.
Conclusion:
Disabling Active Fuel Management on your GM or Chevy engine is a common modification driven by factors like exhaust sound preference, consistent power demand, and concerns about AFM lifter reliability. Whether you choose the comprehensive AFM Delete Kit or the simpler OBD2 AFM Disabler depends on your specific needs, budget, and mechanical aptitude. For many owners of vehicles like the 2006 Trailblazer, an OBD2 disabler might offer a straightforward way to manage AFM. However, for long-term reliability and performance builds, an AFM delete kit offers a more robust solution. Always consider your engine’s condition and your performance goals when making your decision.
