If you own a V6 or V8 Chevy cylinder engine, you may have heard the term Active Fuel Management (AFM). This system switches off half of the cylinders in an engine to minimize fuel consumption during certain driving situations and reactivates them when the driver demands more power.
In other vehicles, this system is known as Active Cylinder Management. In V8, for instance, when the AFM system activates, it turns off half of the cylinders — turning the V8 engine into a V4. In today’s article, I’ll focus on Chevy 8-cylinder to 4-cylinder problems and how to address them. I won’t give much credit to the AFM system.
How does the Chevy V8 to v4 work?
Recently, Chevy has widely adopted its Active Cylinder Management system known as the Active Fuel Management (AFM) system. The Chevy AFM is available on their V6 and V8 engines.
The AFM system deactivates two cylinders from each bank— making your V8 a more efficient V4 engine. This allows the engine to save 5-15% of fuel. However, it results in slightly rougher performance and reduced engine power. The primary goal of the AFM system is to enhance fuel economy and minimize exhaust emissions during operation.
These two primary purposes — improving fuel economy and reducing exhaust emissions are essential as they help Chevy meet environmental regulations and standard emission compliances.
Here’s a simplified explanation of how the Chevy V8 to V4 works.
- When your Chevy engine starts running at a consistent speed while maintaining a steady RPM, the engine load will decrease.
- Some car sensors monitor the engine load, and when it gets to a certain threshold, they signal the PCM/ECM to deactivate two cylinders on each bank.
- The PCM/ECM will activate according to the signal and prevent fuel injection into two cylinders on each bank, successfully switching your V8 into a V4.
- The engine continues running on a V4 mode until it experiences an increased engine load or when you depress the gas pedal to increase the acceleration.
- If any of these happens, the sensors will signal the engine control unit, telling it to send fuel to all the cylinders.
The Chevy Active Fuel Management (AFM) usually works on highways where the vehicle maintains a consistent engine speed and load. When towing loads or during city driving, the AFM system remains inactive, allowing the engine to provide enough power to handle the current situations.
The AFM system effectively does what it is designed for, especially in a V8 Chevy engine. However, there are several Chevy cylinder deactivation problems you should know. I’ll explain them in the next section.
Problems with cylinder management in V8 engines
The most prevalent problems of the Active Fuel Management system in V8 and V6 engines are AFM lifter issues. These lifters are responsible for controlling the opening and closing of the valves, which enables the cylinders to work effectively.
Fuel delivery issues, excessive vibration, rough idling, high oil consumption, worn spark plugs, Active Fuel Management system indicator issues, and carbon buildups are other problems of Chevy Active Fuel Management system.
AFM lifter failures
The most common 2007 Chevy 8-cylinder to 4-cylinder problem is issues with the active fuel management lifter. This problem cuts across all V6 and V8 Chevy engine models and years with the AFM technology.
The AFM lifter is responsible for opening and closing the engine valves, allowing the cylinders to function at peak performance. However, these lifters do not always last the lifespan of the engine.
In almost all Chevy engines with the AFM technology, filter failures are usually common. The replacements are expensive and time-consuming as they require you to dismantle the cylinder heads.
The chances of the lifter getting damaged depend on how frequently the AFM system activates. For instance, if you do more highway driving and maintain consistent engine speed and load, the lifters will fail more frequently than vehicles used more on city driving and towing load. This is simply because the AFM system activates more on highway driving.
Fuel delivery problems
Another 2006 to 2016 Chevy 8-cylinder to 4-cylinder problem is fuel delivery issues. This also cuts across all Chevy engines with the AFM technology. Problems with the fuel delivery systems, such as weak fuel pumps and clogged fuel filters, can lead to insufficient fuel supply when the engine switches back from 4-cylinder mode to all-cylinder mode. This can cause engine hesitation and short-lived loss of power.
Another typical 2014 Chevy 8-cylinder to 4-cylinder problem that cuts across other years is excessive vibration. Some users complained that when switching from 8-cylinder to 4-cylinder, the engine experienced excessive vibration.
Excessive engine vibration during cylinder deactivation and activation transitions can indicate worn or broken engine mounts. Engine mounts secure the engine to the vehicle’s frame and play a crucial role in minimizing vibrations. When they are damaged or worn out, this causes the engine to vibrate excessively when your car is idling or being driven. However, it becomes obvious during cylinder activation and deactivations.
One of the earliest problems with cylinder management in V8 Chevy engines is rough and uneven idling when the engine switches between 8-cylinder and 4-cylinder modes.
Under perfect conditions, the transition between these two modes should be smooth and seamless. However, several factors, such as worn or bad spark plugs, faulty car sensors, and carbon buildups, are the common causes of rough engine idling when switching between 8 and 4-cylinder modes.
According to several Chevy 8-cylinder to 4-cylinder problems forum discussions, rough idling is the earliest and most common problem of AFM.
Newer model Chevy V6 and V8 engines feature advanced engine management systems that can detect any system abnormalities. If the engine management system detects any issue, it will project warning lights on the dashboard, such as a check engine warning light and Active Fuel Management (AFM) indicator.
If the system projects a check engine light, the ECM/PCM will log a trouble code on its memory to tell you the problem. But remember, the check engine warning light can illuminate for several reasons. On some Chevy models with a dedicated AFM indicator, the system will trigger the indicator whenever it detects issues related to the Active Fuel Management system.
Loss of power
Another common problem during an 8 to 4-cylinder modes transition is a short-lived loss of engine power or engine hesitation. While this is not a significant problem, it can be concerning to most drivers, especially when on a date or flirting with their V8 Chevy ride.
Also, misfires can occur during the transition process. The misfire is usually minor, but it will be significant if there are any fuel delivery or ignition issues.
Another problem with the Chevy Active Fuel Management system is high oil consumption without any visible signs of leaks. If the Chevy AFM system goes bad, it will cause high oil consumption. The most feasible way to resolve this problem is to turn off the AFM system on the engine.
Some users say that turning off the Active Fuel management system resolves the high oil consumption issues, while others say it didn’t fix the problem. Don’t worry yet. I’ll explain other ways of addressing the issue later on.
Symptoms of AFM problems
As with several other car components, there are several telltale signs that show you have a faulty AFM system. Pay attention to these signs;
- High oil consumption
- Unstable idle RPM
- Uneven or rough idling
- Vibrations when switching between V8 and V4 mode
- Warning lights on the dashboard and logged error codes.
Problems with the AFM system in cold weather
Cold weather can affect the Chevy Active Fuel Management system in a number of ways. According to some users, the AFM system takes a while before it kicks in during cold mornings.
A user complained that while driving downhill at 70km/h on a cold morning, the engine remained in V8 mode, whereas it usually switches to V8 on sunny days. Another user complained the AFM system refused to kick in during cold mornings until the engine got warm.
The primary problem with the AFM system in cold weather is that it won’t kick in until the engine gets to the average operating temp. You can also notice other issues like hard starting or rough idling during a cold start. However, fuel delivery issues, worn spark plugs, or other ignition system issues can be the culprit.
What are the Solutions to AFM problems?
There are two options on how to fix AFM problems on Chevy engines. The first option is to disable the AFM system, while the second option is to delete it.
I recommend option one if the Active Fuel Management system is still working properly, but you decided not to use it for personal reasons. Disabling the system simply means adjusting the engine ECM/PCM to not activate the AFM system under any conditions.
But if the system is already damaged or malfunctioning, then you have to delete the Active Fuel Management system completely. The Chevy AFM technology uses unique engine parts, such as LOMA cover, AFM lifters, high-volume oil pump, special oil pressure release valve, and different camshafts.
So, deleting the AFM system requires changing all these unique engine parts with non-AFM parts. Oh yeah! You guessed it right. That is an expensive and time-consuming job that requires an experienced mechanic.
How to disable the AFM system?
Disabling the AFM system simply means tricking or reprogramming the engine control module to keep the engine in V8 at all times. To do this, you will purchase an AFM disabler. Then plug the device into your vehicle OBD2 and it will start working immediately. If you ever want to diagnose your car or don’t want to visit your mechanic without it, all you have to do is unplug it.
I mentioned earlier that you can disable the AFM system by reprogramming or tricking the ECM. But here’s the thing, reprogramming your engine may void your vehicle warranty. To prevent this, I recommend you get a Range Technology AFM disabler as it is the only one that does not reprogram your powertrain control module.
How to delete the AFM system?
Deleting the AFM can be tedious and expensive as it requires changing all the unique AFM parts with non-AFM ones. Hence, I recommend deleting the Active Fuel Management system only if the lifters are bad because replacing the lifters is also tedious and expensive.
Here’s a list of what your mechanic will do during the 8-cylinder to 4-cylinder delete:
- Change the AFM lifters with standard ones
- Change the AFM camshafts with standard cams
- Replace the LOMA cover with a non-LOMA cover
- Swap the high-volume oil pump with a standard pump
- Custom tune out the AFM system
- Connect a pressure release valve in the oil pan.
If you don’t have enough cash, discuss with your mechanic whether he will leave one or more of these components in place. You may leave the high-volume oil pump and the LOMA cover to reduce cost. But remember, leaving the high-volume oil pump after a delete leads to excessive oil flow, which will seep into the combustion chamber and burn. Invariably, this results in excessive oil consumption in the long run.
Should you worry if your Chevy engine doesn’t go to 4-cylinder mode?
If the V8 does not go into a 4-cylinder mode when driving on a highway at a consistent engine speed and load, and at average operating temperature, it could mean there’s an issue with the AFM lifters. Ignoring this issue for an extended period can cause more damage to the lifters.
However, it’s okay if the V8 does not switch to V4 when towing load, running city-driving, or during cold weather. The engine has to reach the average operating temperature before the AFM system will kick in. And the vehicle has to maintain a steady engine load and speed. So, if you keep pressing the gas pedal hard, don’t expect the Active Fuel Management system to activate.
To sum it up, the common Chevy 8-cylinder to 4-cylinder problems are high oil consumption, AFM lifter failures, excessive vibration, and warning lights. The high oil consumption can lead to lower oil pressure and low oil level and cause several major engine components like the timing chain and tensioner to fail.
If you don’t care about saving that little extra cash on fuel, then you can disable or delete the Active Fuel Management system to save on related AFM repairs. Not only will deleting or disabling the system increase your exhaust sound, but it’ll also keep your engine at V8 at all times.