In order to meet stricter emissions regulations, the LLY replaced the LB7 engine and was the first Duramax to use EGR emissions technology. Unfortunately, the new EGR system was problematic leading to common valve failure. Aside from this addition the new engine received a variable vane turbo and eventually got some block and internal upgrades in 2006, further strengthening reliability.
The new upgrades to the LLY removed some of the common LB7 problems such as fuel injector and fuel pump failure. However, there are a number of new issues that have arisen due to the changes, and a number of shared problems with the LB7. Additionally, 2006 LLY models are very comparable to the LBZ engine, creating a number of overlapping common problems there as well.
The Duramax LLY engine suffers from problems with bent rods, blown head gaskets, EGR valve failure, glow plug failure, overheating, and fuel pressure relief valve failure.
Duramax LLY Reliability
Ultimately, despite the common problems we are going to discuss in-depth below, the LLY is still a very reliable engine and has proven capable of making it to the 300,000 mile mark with minimal issues.
Two of the common problems, bent rods and the FPRV, are really only common on tuned and modified LLY’s running high power levels. The EGR problems only become an issue at high mileage. Glow plug issues are more than likely fixed on any LLY by now. And overheating and head gasket failure can be prevented with an upgraded turbo inlet manifold.
Overall, the common problems here are all avoidable and preventable. The block and internals on the LLY Duramax have stood the test of time. With common and consistent maintenance, these engines are superbly reliable, especially when left in stock form.
Duramax LLY Engine Problems
- Bent rods
- Head gasket failure
- EGR valve failure
- Glow plug failure (2006 only)
- Overheating (pre-2006)
- Fuel pressure relief valve
If you would rather consume this content via a video, check out our Chevrolet LLY Duramax Common Problems video below:
1. Bent Rods
While the LLY made competitive performance numbers back in 2004, the engine is certainly not competitive to the modern day diesels. For this reason, adding performance modifications to the Duramax is a common route to improve performance and hauling capacity. While light modifications such as intakes, exhausts, and modest tunes shouldn’t cause any problems, bigger or more aggressive modifications can.
The LLY uses the same forged-steel rods as the LB7 used. These rods were some of the lightest used in any Duramax (outside of the LML). In addition to a higher compression ratio, the VVT turbo which produces significantly more torque at lower RPM’s, the LLY rods are more susceptible to bending at increased power levels. Once you break the 500whp mark, bent rods becomes a likely reality. Additionally, be cautious of any modifications which create significant low-end torque as low-end torque is the primary killer of rods.
2. Head Gasket Failure
The LLY has the largest turbo in it out of any other 6.6L Duramax variants. Outside of it being the largest turbo, it had the largest compressor wheel and the tallest exhaust vanes. The end result is having an extremely efficient and high-flowing turbocharger. While this is great for those looking to add significant horsepower, this is bad for head gaskets.
Aside from the large turbocharger, the problem is amplified by the size of the turbo inlet manifold / mouthpiece. The inlet manifold is small and highly restrictive in its design. The restriction decreases turbocharger efficiency and makes the turbo have to spool faster to produce adequate boost which creates hotter engine temperatures. When you couple that with the biggest compressor wheel, the turbo has to work extremely hard which increases cylinder pressure and heat.
Over time head gaskets naturally deteriorate and fail due to the heat and pressure they are subject to. When you add the excess heat produced by the turbo with an undersized cooling system, the gaskets fail frequently.
Head Gasket Failure Symptoms
- White smoke from the exhaust
- Leaking water out of the tailpipe
- Discolored oil and foamy residue in the oil cap
- Engine overheating
- Coolant leaks on the engine block and garage floor
While the replacement option is as easy as replacing the head gasket with a new $40 part, getting to the head gasket and properly cleaning and applying a new gasket is challenging. There are approx. 20 major parts that need to be removed to access the gasket. Book labor time for the job is 40 hours which can easily eclipse $4k of labor alone with today’s hourly shop rates.
3. EGR Valve Failure
Unfortunately, exhaust gas circulation (EGR) systems were standard on every Duramax LLY produced. The EGR system included a EGR valve and cooler. At a high level, the EGR system recirculates exhaust air back through the engine so that it can be re-burned in the combustion cycle, reducing the amount of nitrogen oxide released into the atmosphere.
The EGR valve is responsible for determining when and how much exhaust gas is recirculated into the intake manifold. Because you don’t want to shoot hot exhaust air into the engine, you also have an EGR cooler which is responsible for cooling the air that is recirculated. To cap off the emissions features, you also have a catalytic converter in the turbo downpipe to further filter exhaust air.
EGR system failure is not common on low-mileage LLY’s, but the valve, cooler, and catalytic converter are all common failure points for high-mileage engines.
EGR Failure Symptoms
- Rough idling
- Poor performance and sluggish acceleration
- Engine stalling
- CEL codes for EGR issues or AFR related codes
4. Glow Plug Failue – 2006 Only
In 2006, the glow plugs were paired with a problematic glow plug module. The glow plug module was known to overload the plugs with current, causing the ends of the plugs to actually break off which would cause catastrophic engine damage.
The good news is that fixing this issue is as simple as re-programming the control module, which the dealership would do for free. Nowadays, this problem has probably been fixed on 98% of these engines out there, but if you are buying a low-mileage 2006 LLY it makes sense to confirm that this reprogramming has happened.
Common Glow Plug Failure Signs
While this issue won’t have any warning signs, I wanted to provide some symptoms of failure since these things are like spark plugs and do need to be replaced from time to time. Fortunately, they are inexpensive and pretty easy to DIY replace on these engines.
- Starting issues – slow or hard starting
- Poor idling and misfires
- Engine light for glow plugs
5. Overheating in Pre-2006 Models
In the head gasket failure section above we discussed how the LLY diesel is subject to high heat levels due to the turbocharger and design of the turbo inlet. Additionally, the pre-2006 models had smaller radiators and cooling fans. The combination of added heat and a small cooling system can lead to frequent overheating on pre-2006 LLY models. However, overheating tends to really only be a problem when are towing heavy loads in really hot temperatures.
In 2006 year models, the turbocharger was improved to increase efficiency and reduce heat generation. Additionally, the size of the inlet manifold increased and was redesigned to prevent the heat issue from the previous year models. The engine was also outfitted with a larger radiator and cooling fan to improve cooling capacity and prevent overheating.
One of the best reliability mods for the LLY is upgrading to a larger and less restrictive turbo inlet.
6. Fuel Pressure Relief Valve
The fuel rail on the 6.6L Duramax injects fuel at nearly 23,000-26,000psi of pressure. Included on the fuel rail is a pressure relief valve which is a spring-loaded valve on the back side of the fuel rail. The valve’s job is to release pressure in the event that it becomes too high. When pressures surpass the allotted threshold, the spring compresses, releasing rail pressure.
Over time, from constantly being subjected to extreme pressure, the spring can weaken, causing it to being releasing rail pressure earlier than it should. The end result is rail pressure continually dropping slowly over time which will make your Duramax create less and less power. So you will end up with continually decreasing power.
While this problem is only common on tuned and modified LLY’s, replacing the spring valve with an aftermarket valve or simply a new OEM valve should solve any potential problems here.
Common FPRV Symptoms
- P0087 engine code (low fuel rail pressure)
- Decreased performance
- Noticeable decline in power
- Engine misfires
- AFR codes running lean