Are you hearing an annoying engine rattle or ticking noise at idle? Is your ride suffering from rough idling, misfires, and lacking power? These are common symptoms of Active Fuel Management (AFM) lifter failure, an issue that plagues many GM truck and SUV owners. But what exactly causes AFM lifters to fail and how can you prevent it?
In this comprehensive guide, we’ll cover:
- What are AFM lifters and how do they work
- The most common causes of AFM lifter failure
- Symptoms to watch out for
- Tips to prevent AFM lifter problems
- When to replace bad lifters
- DIY or mechanic for replacement?
- Frequently asked questions
So if you want to stop worrying about unpredictable AFM lifter issues, keep reading. This guide will equip you with the knowledge to recognize AFM lifter failure symptoms early and take action to avoid significant engine damage down the road yo.
Table of Contents
What are AFM Lifters and How Do They Work?
First, let’s quickly cover what exactly AFM lifters are and what they do.
AFM, also known as Active Fuel Management, is a cylinder deactivation system used by GM in some of their truck and SUV engines like the 5.3L V8. AFM allows the engine to seamlessly switch between operating on 8 cylinders or 4 cylinders under light load conditions.
This improves fuel economy when full power is not needed. The engine computer controls special lifters on half the cylinders that can collapse to stop valve operation, effectively deactivating those cylinders.
AFM lifters are different from regular lifters because they contain a locking pin that hydraulically collapses the lifter when needed for cylinder deactivation. This occurs at cruising speeds when power demands are low. AFM lifters re-inflate when the computer prompts, reactivating the cylinder and allowing the valve to open again.
Now you know the basics of how AFM lifters operate. But occasionally, they can start to fail prematurely, leading to some worrisome engine issues. Next, let’s look at what causes these pesky AFM lifter problems.
Common Causes of AFM Lifter Failure
AFM lifter failure typically results from a loss of oil pressure or volume to the lifters, which prevents them from operating properly. Here are some of the most common root causes:
Worn Camshaft Lobes
The camshaft lobes are what actually push down and open the lifters as they rotate. If the cam lobe profiles become excessively worn from high mileage, they won’t provide enough lift to properly pump up collapsed AFM lifters. Worn lobes are a common cause of AFM ticking noises and misfires.
Excessive Valve Lash
Too much gap or “lash” between the tip of the rocker arm and valve stem can prevent full lifter inflation and lead to failure. Valves and rockers should be adjusted to factory specs.
Clogged AFM Oil Control Valves
Each AFM lifter has a tiny oil control valve that regulates oil flow to inflate and collapse the lifter. Carbon buildup can clog these valves, disrupting proper lifter operation.
Low Oil Pressure
If engine oil pressure drops due to a worn pump, blocked pickup, or diluted oil, the AFM system may not receive adequate pressure for lifter operation. Low oil pressure usually affects all lifters.
Fuel, coolant, or excessive sludge contamination thins out oil and reduces lubrication ability, starving components like AFM lifters. Change oil regularly and fix any leaks that could contaminate oil.
Now that you know what causes AFM lifters to fail, let’s move onto the symptoms to watch out for. Recognizing these warning signs early is key to avoiding major engine damage from collapsed lifters.
Symptoms of Failing AFM Lifters
When AFM lifters start to fail, whether from a loss of oil pressure or volume, contamination, or another issue, some telltale symptoms will arise. Here are the most common:
Constant Rattling or Ticking Noise from Valvetrain
The most common sign of a collapsed AFM lifter is a loud rattling or ticking noise coming from the top of the engine. This noise is most noticeable at idle when the engine is warmed up. It results from the rocker arm tip rattling on top of a collapsed, inoperative lifter that cannot inflate to close the gap.
Failed AFM lifters prevent smooth opening and closing of intake and exhaust valves. This can cause rough idling as the engine struggles to run on cylinders with collapsed lifters. Misfires may be felt as shaking or juttering.
When an AFM lifter fails to inflate, its cylinder may not fire, resulting in misfires. This causes power loss and rough running. Misfires will trigger the check engine light.
Check Engine Light
The engine computer detects misfires and problems with the AFM system through various sensors when lifters start to fail. This illuminates the check engine light with trouble codes like P0300 random misfire detected, P0306 cylinder 6 misfire, or P050D for an AFM system performance issue.
Ticking Noise on Startup
It’s common for all engines to exhibit some valvetrain ticking on a cold start that quietens down as oil reaches the top end. But if the ticking persists for more than 30 seconds to a minute on a warmed up engine, it could point to a collapsed AFM lifter.
Now that you know what failing AFM lifters sound and feel like, let’s get into some proactive maintenance tips to help prevent these issues in your engine. A little prevention goes a long way!
How to Prevent AFM Lifter Failure?
While AFM lifters are a common failure item, especially at higher miles, there are some steps you can take to reduce the chances of premature failure and avoid repairs:
Use Quality Full Synthetic Oil and Change Regularly
One of the best things you can do is use a top rated full synthetic engine oil like Amsoil Signature Series or Mobil 1. Quality synthetic oil maintains viscosity at high temps, resists shearing, and prevents deposit buildup much better than conventional oil. This ensures the AFM system gets adequate oil pressure and volume. Stick to 5,000 mile oil change intervals, or earlier if indicated by the oil life monitor.
Replace AFM Lifters at Recommended Service Intervals
GM recommends replacing the AFM lifters every 50,000 miles in most applications. This prevents worn components from failing. If you haven’t replaced them by 100k miles, it’s a good idea to be proactive about a lifter replacement service.
Clean AFM Oil Control Valves and Screens
The small oil control valves in AFM lifters can become clogged over time, especially if oil changes were neglected. Cleaning the valves and screens prevents restricted oil flow and allows proper lifter operation. This can be done along with a routine lifter replacement service.
Fix Any Causes of Low Oil Pressure
Keep an eye on oil pressure at higher mileages and make necessary repairs if it drops too low, such as replacing a worn oil pump or pickup screen. This ensures adequate oil supply to the AFM lifters.
Listen for Valvetrain Noises
Keep your radio off and windows down when at idle listening for the telltale ticking associated with collapsed lifters. Address any noises right away before it leads to major damage. Early intervention is key.
Another question that arises is when you should actually replace failed AFM lifters that are causing symptoms. Let’s take a look.
When to Replace AFM Lifters?
Since AFM lifter replacement requires significant labor and expenses, you don’t want to replace them prematurely if the noise or misfire is due to another cause. Here are signs it’s definitely time for new lifters:
Constant Ticking/Rattling at Idle
If the valvetrain ticking noise persists when the engine is fully warmed up and does not quiet down after 30 seconds to a minute, it likely means one or more collapsed lifters. Any constant rattle indicates they should be replaced.
If you have cylinder specific misfire codes alongside a ticking noise, it points to failed AFM lifters as the cause. Misfires mean the valves are not opening due to collapsed lifters, requiring replacement.
Oil Pressure is Within Spec
Low oil pressure can cause similar symptoms, so verify it’s within specifications before condemning the lifters. Ruling out an oil pressure problem confirms replacement is needed.
In severe cases of collapsed AFM lifters, damaged valvetrain components like bent pushrods can also result. So the sooner you address failed lifters, the better.
Now let’s discuss whether replacing AFM lifters is a DIY project or best left to a professional mechanic.
DIY or Mechanic for AFM Lifter Replacement?
Replacing faulty AFM lifters in your 5.3L, 6.0L or other V8 isn’t the easiest job, especially for the DIY novice. Here are some factors to consider:
- The process involves dropping the oil pan to access the lifters which requires unbolting pan and components, lowering the engine with a hoist, resealing gaskets, etc. Special tools are required.
- With labor, a shop will charge around $1,000 or more for parts and service. DIY you’re looking at around $300-400 in parts alone.
- There is a risk of getting metal shavings or debris in the engine if you’re not very meticulous in your work.
- However, if you have automotive experience and are capable, DIY replacement can save substantial labor costs. Having an extra set of hands helps.
Carefully weigh the pros and cons of your mechanical skill and budget when deciding between DIY or professional AFM lifter replacement. Either way, take action promptly if your engine exhibits any warning signs.
We’ve covered a lot about identifying and preventing AFM lifter failure. Let’s recap a few of the most common questions for reference:
Frequently Asked Questions
How long do AFM lifters last?
GM states AFM lifters should be replaced around 50-60k mile intervals. But they can last up to 100k+ miles if properly maintained before failure occurs. Higher mileage increases the chances of worn components causing problems.
Why do AFM lifters fail prematurely?
The main causes of premature failure are lack of oil pressure/volume, contamination from negligent oil changes, and high mileage wear exceeding the lifter’s operational lifespan. Follow the tips above to maximize lifespan.
Can bad gas cause AFM lifters to fail?
While low fuel quality or octane isn’t directly linked to AFM lifter failure, it can potentially cause pre-ignition and engine damage that may lead to oil pressure problems affecting the AFM system. Use top tier gas.
Is AFM lifter tick/rattle normal on startup?
Some brief ticking noise on a cold start is normal as oil reaches the top end, but should quiet down within 30 seconds or a minute once warmed up. Consistent rattle indicates an issue.
Dealing with collapsed AFM lifters causing engine noise, rough idle, misfires and power loss is not fun. But understanding the root causes of failure along with symptoms allows you to address problems proactively. Focus on preventative maintenance before expensive repairs are needed. And if replacement is required, decide whether to DIY or have a professional handle it.
With the information covered in this guide, you can confidently maintain your AFM-equipped engine and deal with any lifter problems that may arise before it leads to permanent damage. Just remember to stay vigilant in listening for symptoms, change oil regularly, and don’t neglect scheduled component replacement intervals.