Driving a Chevrolet vehicle model with an 8-cylinder engine guarantees reliable power and performance. However, such an engine will prioritize power over fuel efficiency. Luckily, some models, like the Chevy Silverado, feature the Active Fuel Management (AFM) system to increase fuel economy.
This system shuts down four cylinders in your V8 engine, turning it into a V4 engine. Unfortunately, the transition between 8-cylinder and 4-cylinder modes might come with several issues. If you’re a proud owner of such a vehicle, you might want to know how to deal with those problems.
I detail the most common Chevy 8 cylinder to 4 cylinder problems, plus effective solutions. You’ll also know what the AFM system means and how it works.
Question: What is the Chevy AFM System?
The AFM system is a cylinder management technology in some Chevy V6 and V8 engines. It shuts off half of an engine’s cylinders to reduce power levels and fuel consumption. The system kicks in during highway driving as the engine experiences reduced loads.
AFM system in Chevy V8 engines deactivates four cylinders, converting your mighty V8 engine into a fuel-efficient V4 engine. As a result, your engine will lose almost half of its power but consume approximately 30% less fuel.
If you’re an eco-conscious vehicle enthusiast, you’ll love this system due to its emission-reduction capabilities. With enhanced fuel efficiency, you can expect your Chevy vehicle to cut down on exhaust gasses.
Question: How Does the Chevy AFM System Work in 8-Cylinder Engines?
A Chevy vehicle with this system has special sensors for monitoring engine load while driving. These sensors communicate with the ECU to ensure shifting between 8-cylinder and 4-cylinder modes.
When driving at a constant speed, particularly on open highways, the load on your cylinders tends to decrease. The special sensors will signal the ECU when the load reaches a certain threshold. In this case, the ECU stops delivering fuel to four cylinders – two cylinders on each side.
Your Chevy vehicle will continue operating as a V4 engine until the load on the cylinders increases. This happens when you press down the pedal to accelerate. The special sensors will signal the ECU to inject fuel into all cylinders, shifting the engine from V4 to V8.
Note: The AFM system remains inactive when towing heavy loads or climbing a grade. The sensors will detect the high demand for power and command the ECU to continue injecting fuel into all cylinders.
Answer: Common Chevy 8 Cylinder to 4 Cylinder Problems
The constant transition between V8 and V4 modes might trigger the following problems:
- Lifter failure
- Power loss
- Rough idle
- Excessive engine vibrations
- Check engine light
Lifter Failure
One of the most reported issues with the AFM system is lifter failure. Lifters allow the valves in the combustion chamber to open or close. The opening and closing of these valves let fuel in the engine and exhaust out.
Lifter failure is prevalent in AFM-equipped engines, especially when the system stays activated for a long time. For example, if you drive on highways, the AFM will work constantly, causing premature wear and tear of lifters.
Worn-out lifters might fail to close and open the valves, leading to severe engine damage.
Loss of Power
Engine losing power when shifting between the two cylinder modes is another issue you might encounter. This issue can occur if your fuel delivery system has a problem.
A failing fuel pump or clogged injectors will prevent adequate fuel supply when reactivating all cylinders. As a result, you might notice an engine hesitation or temporary loss of power when accelerating.
Engine misfires are also common when transitioning between cylinder modes. Misfires happen when there’s an inadequate fuel supply or a defective ignition system. A misfiring engine will cause a temporary loss of power when accelerating.
Rough Idle
Another Chevy 8 cylinder to 4 cylinder problem is rough or uneven engine idle. The transition between cylinder modes should be seamless, allowing your engine to run smoothly. However, some issues within the internal combustion engine can prevent a seamless transition.
For example, sensors monitoring engine load can malfunction and provide inaccurate data. As a result, the engine might experience jerky transitions and idle roughly.
Worn spark plugs could also be to blame. Fouled plugs will cause incomplete combustion in the cylinders. An incomplete combustion will trigger a misfire during cylinder mode transitions, causing a rough idle.
Excessive Engine Vibrations
Several issues can cause your engine to vibrate. But if vibration occurs during cylinder mode transitions, the AFM system could be to blame.
Excessive engine vibrations might stem from defective solenoids, actuators, or valves. These components ensure a smooth transition between the 8-cylinder and 4-cylinder modes. If they malfunction, you might notice an abnormal vibration and rattling noises.
Worn or broken engine mounts can also lead to excessive vibrations during cylinder mode transitions.
Check Engine Lights
Chevy 8 cylinder to 4 cylinder problems will cause check engine lights to pop up on your dash. These warning lights might occur due to defects in the system.
With the help of sensors, the ECU will detect issues in the system and record diagnostic trouble codes. Additionally, various warning lights will appear on the dash, indicating faults within the engine.
Answer: How to Fix Chevy 8-Cylinder to 4-Cylinder Problems
Here’s how to solve the mentioned issues.
Check for DTCs
Diagnostic trouble codes communicate the health status of your engine. Use a diagnostic scanner to retrieve and read the trouble codes recorded in your ECU. You’ll need to pay attention to any error codes related to components within the AFM system.
Repair or replace Worn Lifters
Repairing or replacing lifters is a complex procedure that entails disassembling cylinder heads. If your lifters are to blame, hire a professional to repair or replace them.
Examine the Fuel Delivery System
Inspect the injectors for clogs and clean them with a fuel injector cleaner. If the injectors fail to deliver fuel to the engine after cleaning, examine them for signs of wear or damage. Replacing worn or damaged injectors will help resolve fuel delivery issues.
If your engine is still struggling with insufficient fuel, check the fuel pump for defects. Clean the pump with a fuel system cleaner and replace the filter if it looks clogged. If cleaning this pump won’t help, allow an authorized mechanic to repair or replace it.
Clean or Replace the Sensors
Over time, sensors working with the AFM system can malfunction due to dirt, corrosion, or regular wear. Locate and examine the camshaft position and oxygen sensors. You can use a specialized cleaning solution to remove dirt or corrosion from the sensors.
If you find worn or damaged sensors, follow the manufacturer’s guidelines to replace them.
Replace Worn or Fouled Spark Plugs
Check the spark plugs to see if they’re dirty, worn, or broken. Wipe the dirt out with a rag and reinstall the plugs. You must tighten the plugs to the recommended torque and angle. If your plugs appear worn or broken, replace them with the correct type.
Replace Worn or Broken Engine Mounts
Engine/motor mounts secure the engine to your Chevy vehicle’s frame to minimize vibrations. These mounts wear out or break down over time due to collisions, bumpy rides, and excessive braking. Inspect and replace any worn or broken engine mounts to resolve vibration issues.
If none of these fixes resolves AFM system problems, take your vehicle to an authorized mechanic or Chevy dealership. These professionals will use advanced diagnostic tools to retrieve trouble codes and fix the root problem.
It’s worth noting that resolving this problem will help clear all the check engine lights. If they fail to turn off, drive for a few miles or reset the vehicle’s computer.
Final Thoughts
Chevy cylinder modes transition between 8 and 4 cylinders helps to increase fuel efficiency while minimizing emissions. However, this transition is likely to cause some problems in your vehicle.
The most common Chevy 8 cylinder to 4 cylinder problems include lifter failure, rough idling, loss of power, excessive vibrations, and check engine lights turning on. Fix these problems as soon as possible to prevent further damage to engine components.