Common GMC 6.2 V8 Engine Problems That You Should Know

The GMC 6.2-liter V8 pushrod engine is well-known for its power and reliability, but like any engine, it’s not immune to problems. Some owners have reported common faults such as collapsed lifters, carbon buildup, and fuel injector failures – some of which can be quite expensive to fix.

Most of these GMC 6.2 V8 engine problems stem from key design features like Active Fuel Management (AFM) and direct injection. While they’re both there to help with improving your fuel economy and performance, they also introduce potential weaknesses and points of failure over time.

Then, there are also common wear-and-tear issues, such as leaking intake manifold gaskets and broken exhaust manifold bolts, both of which can further affect the engine’s longevity. So, without further ado, let’s break down in more detail the most common GMC 6.2 engine problems, what causes them, their symptoms, and how much it costs to fix them.

GMC 6.2 Engine Problems – Cheat Sheet

Now, while we will be discussing each of these common GMC 6.2 engine problems in more detail further below, here’s a quick TL;DR cheat sheet to compare these issues at a glance:

Problem	Main Cause	Fix	Estimated Cost
Lifter Collapse & Bent Pushrods	AFM system fails, causing lifter collapse	Replace lifters and pushrods, or delete AFM	$1,000+
Carbon Buildup	Direct injection fails to clean intake valves	Perform walnut blasting or intake valve cleaning	$500+
Fuel Injector Failure	Clogged or worn injectors restrict fuel flow	Replace injectors and fuel pump	$2,000+
Leaking Intake Manifold Gaskets	Gasket material deteriorates over time	Replace intake manifold gaskets	$200–$500
Broken Exhaust Manifold Bolts	Heat cycling weakens and breaks bolts	Extract and replace bolts	$1,000+

Top 5 Most Common GMC 6.2 Engine Problems

Among the design changes and engineering updates seen in GMC’s L86/L87 6.2 V8 is the use of an all-aluminum block. It’s a super lightweight design, and to ensure it could take the punishment from all that compression, it still uses iron cylinder sleeves. Plus, the GMC 6.2’s cylinders are positioned at a 90-degree angle, just like classic pushrod designs.

Just like all other Gen 5 blocks, the GMC 6.2 L86/L87 features a 103.25mm bore and a 92mm stroke. Since it uses a pushrod design, these V8 engines don’t use an overhead camshaft, unlike other modern V8s. Still, pushrod engines are well-regarded and proven for their superior long-term reliability, and they’re also cheaper to run and cheaper to maintain.

Aside from these, there are two new additions to these engines that feature prominently when looking at GMC 6.2 engine problems… Direct injection, as well as GM’s AFM (active fuel management). The latter is otherwise known as ‘displacement on demand’, whereby some of the cylinders can turn off, allowing the engine to save fuel while driving.

With that in mind, here are some of the most common GMC 6.2 engine problems:

1. Lifters Collapsing And Causing Bent Pushrods

General Motors’ AFM (Active Fuel Management) allows GMC’s 6.2 V8 to basically just run on 4 mere cylinders if they’re not being used. This is meant to help improve fuel economy. The bad news here is that the AFM system actually (inadvertently) causes damage to the engine’s pushrods. This is mainly due to the complex lifters that GMC uses for the AFM.

These complex lifters are prone to collapsing, thus causing other issues, such as bent pushrods. Symptoms you might experience as a consequence include a decrease in power or performance. The only real fix is to replace these lifters outright. Not to mention, needing to replace the damaged pushrods. If your GMC is new, it may be covered under warranty.

Although, if you’re buying an older GMC (or Chevy, or other GM vehicle that features AFM), this is a big deal, since fixing it is rather costly… $1,000 or likely more. If you’re looking to prevent this from happening at all, some owners opt to disable or delete the AFM entirely. This is a pretty expensive procedure too, but at least it’ll prevent collapsed lifters and bent pushrods.

2. Excessive Carbon Buildup

Aside from the AFM, the adoption of direct injection in GMC’s L86/L87 6.2-liter V8 engines has also proven problematic. Just like on a lot of other cars, direct injection here has caused a carbon buildup problem with the GMC 6.2 engine. This is different from the older GMC/Chevy/GM engines, which use port injection. The fuel delivery was not as precise back then.

However, the side effect was that the design was good enough to clean off the intake ports. Thus, preventing carbon buildup. On the other hand, direct injection doesn’t manage self-cleaning as effectively, which causes carbon buildup to occur. In some cases, this could happen every 60,000 miles. And, if not fixed, it ruins the performance and efficiency of your truck.

The only way to fix this would be to clean your intake valves with walnut blasting. Or, you could take it to a dealership or service center, and let them clean it off with special machines. It’s not an expensive repair job either, with the basic carbon buildup cleaning process costing you $500 or more. But hey, this ought to stave off carbon buildup for another 60,000 miles.

3. Direct Injection Pump And Fuel Injectors Failing

Another downside of this direct injection system that adds to the pile of GMC 6.2 engine problems is that the direct injection pump and fuel injectors regularly fail. These things have very tight tolerances. So, if you fill up with gas that has even microscopic impurities, it will fail. If you’re buying an old GMC truck, make sure to check the pump and the injectors.

Otherwise, it’ll cost you quite a bit of money to get all this sorted out… $2,000 or so is a good estimate. Between the carbon buildup issues and the easily worn-out pump and injectors, some owners have even contemplated mods to swap out the default direct injection system for old-school port injection. It’s not easy, but some reckon it’s a feasible project.

4. Intake Manifold Gaskets That Leak

Other than that, this is mainly a problem with higher mileage GMC vehicles with the 6.2 engine, but there are noteworthy issues with the intake manifold gaskets. The cause is found to be the material these intake manifold gaskets are made of. Over time, the material hardens, made worse by age, heat exposure, and regular wear and tear, and now, it won’t seal well.

When there is not enough of a good seal in the intake manifold, there’ll be a lot of unmetered air entering the engine. This means that you’ll often see a check engine light (CEL), not to mention the performance impact it has on the engine. A lot of unmetered air in the engine makes it run lean. Thus, causing your ECU to automatically dump more fuel into the engine.

This ultimately worsens your fuel economy and has other performance impacts and concerns regarding the engine’s longevity. The only good thing about this problem is that it’s not that expensive to fix. You could even do it yourself… The intake manifold gasket is on top of the engine. And, you only have to remove a few components to get to it, before replacing it.

5. Broken Exhaust Manifold Bolts

Another notable GMC 6.2 engine problem is the exhaust manifold bolts, which are prone to breaking. Unfortunately, these aren’t cheap or easy to fix. What is bad, though, is that you have to replace them if you want to prevent exhaust leaks from happening. These leaks can cause exhaust gases to get inside your cabin, not to mention causing other issues.

One of those side effects is the check engine light (CEL) turning on. This is activated because the O2 sensor is getting incorrect airflow readings. This lets your truck’s computer know that something is wrong. Another common symptom that you might notice with broken exhaust manifold bolts is a hissing sound, normally from the front, where the engine is.

Repairing this is probably going to be pretty expensive. This is because a lot of parts have to come off for a mechanic to be able to reach the engine. You can’t realistically expect this to get sorted under $1,000 or more since there’s a lot of work required. As a whole though, despite these issues, in general, the GMC 6.2-liter V8 engine is comparatively really reliable.

GMC 6.2 Engine Maintenance Table

With problems like AFM lifter failure, carbon buildup, and injector clogging, you might be understandably hesitant to get a GMC 6.2 engine. However, performing proactive maintenance can significantly reduce the chances of these problems occurring, and keep your GMC 6.2 engine ticking away smoothly for 200,000+ miles.

To give you an idea of what you can do servicing-wise, we’ve prepared this handy GMC 6.2 engine preventive maintenance table and servicing schedule:

Issue	Preventive Maintenance	Recommended Interval
AFM/DFM Lifter Failure	Use high-zinc full synthetic oil (Dexos-approved), change oil regularly, and consider an AFM/DFM delete if longevity is a concern.	Oil change every 5,000 miles
Carbon Buildup (Direct Injection)	Use a catch can, run a PFI (Port Fuel Injection) cleaning additive, and perform walnut blasting if buildup worsens.	1) Catch can: Install ASAP 2) PFI Additive: Every 5,000 miles 3) Walnut blasting: Every 50,000 miles
Fuel Injector Clogging	Use high-quality fuel (Top Tier 91+ octane) and periodically add injector cleaner.	Injector cleaner every 10,000 miles
Timing Chain Wear	Monitor for rattling noises, use high-quality oil, and avoid excessive towing strain.	Inspect at 100,000 miles
Transmission Overheating (10L80 & 8L90 issues)	Flush transmission fluid regularly and consider an aftermarket cooler for heavy towing.	A fluid change every 50,000 miles

By following these preventive maintenance tips, you could easily extend the life of your GMC 6.2 engine, reduce repair costs, and avoid common failures. Simple actions like using high-quality fuel, synthetic oil, and proper cleaning methods can make a huge difference in long-term reliability.

What Is The GMC 6.2 Engine?

Launched as a replacement for the Gen IV Vortec, now the so-called EcoTec3, GMC’s all-new 6.2-liter V8 pushrod engine was as widespread as General Motors itself. Common designations and variants like the L86/L87 were used mainly in trucks, like the Silverado, Sierra, Tahoe, Yukon, Escalade, and Suburban. Nonetheless, there are GMC 6.2 engine problems to be wary of.

Then, there was the LT1, used in the C7 Corvette and the Camaro, as well as the LT2, used in the C8 Corvette. Not to mention, the LT4, which was used for the Corvette Z06, Camaro ZL1, and other high-performance vehicles in GM’s stable, as well as the LT5, used in the Corvette ZR1, one of the most powerful engines ever made. For now, though, we’ll focus on the L86 and L87.

For the most part, GMC’s L86 and L87 V8s are highly reliable and durable powertrains, for long-term ownership and where minimal maintenance is needed. There are never any questions about the longevity of the engine block, given that it’s a proven design. However, some of that newer tech is what causes those aforementioned GMC 6.2 engine problems.

GMC 6.2 Engine Pros & Cons

The GMC 6.2 EcoTec3 V8 is an excellent engine for power, towing, and resale value. However, as we’ve discussed thus far, AFM lifter issues, carbon buildup, and high maintenance costs are drawbacks that you have to consider. If it’s been well-maintained or if it’s been modified (AFM delete), it can be a strong, reliable engine that lasts well over 200,000 miles.

If you’re still unsure about whether the GMC 6.2 engine is or isn’t the right choice for long-term ownership, let us break down its respective pros and cons to make things easier for you:

Pros	Cons
Excellent Power – 420 hp & 460 lb-ft of torque for strong towing & acceleration	AFM Lifter Issues – The Active Fuel Management system is prone to lifter failure
Good Fuel Economy (for a V8) – Cylinder deactivation improves MPG on highways	Carbon Buildup – Direct injection leads to intake valve deposits over time
Advanced Technology – Features like DFM (Dynamic Fuel Management) improve efficiency	Expensive Repairs – Lifter replacement, fuel injectors, and carbon cleaning can cost thousands
Strong Reliability (If Maintained Well) – Can exceed 200,000 miles with proper care	Premium Fuel Recommended – Best performance requires 91+ octane, increasing running costs
High Resale Value – Holds value better than many competitor V8s	Not as Reliable as Ford 5.0L – More mechanical issues compared to Coyote V8

GMC 6.2 vs Ford 5.0 Coyote vs RAM 6.4 HEMI

While we’ve concluded that GMC’s 6.2 engine is well-known for its power and efficiency, how does it hold up against rival engines from Ford and RAM? Specifically, we’re comparing GMC’s 6.2L EcoTec3 against Ford’s 5.0L Coyote and RAM’s 6.4L HEMI, in terms of performance, reliability, durability, common problems, longevity, and maintenance costs.

After a bit of research, here’s how these three engines stack up:

Engine	Durability	Common Issues	Estimated Maintenance Costs	Real-World Longevity
GMC 6.2L EcoTec3	200,000+ miles with proper care	AFM lifter failure, carbon buildup, and fuel injector issues	Moderate to high ($1,000+ for lifter repairs)	Reliable if AFM is disabled, with some high-mileage examples over 250k miles
Ford 5.0L Coyote	250,000+ miles with good maintenance	Timing chain wear, as well as oil consumption issues	Moderate ($1,500+ for timing chain replacement)	Proven longevity, especially seen in some Mustangs and F-150s
Ram 6.4L HEMI	200,000+ miles with good maintenance	Lifter tick, camshaft wear, and MDS (cylinder deactivation) failures	High ($2,000+ for camshaft replacement)	It could last long, but lifter and cam issues can be costly to fix

In short, if you’re talking about reliability, here’s our takeaway:

• The Ford 5.0L Coyote is often considered the most reliable due to fewer major design flaws and high-mileage durability.
• The GMC 6.2L EcoTec3 is strong but suffers from AFM-related failures and direct injection issues. However, AFM deletes and regular maintenance greatly improve reliability.
• The Ram 6.4L HEMI is powerful but has serious lifter and camshaft issues, which can be expensive to fix.