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The LML Duramax was designed and released in response to new emissions standards that began in 2011. However, the LML was also released to celebrate the 10th anniversary of the Duramax engine. With more power, improved emissions, and a fuel system upgrade, the LML boasted a long list of major changes.
According to GM, over half of the internals in the newly released LML were replaced from the previous engine. Some new parts included a beefier block, lighter rods, and new pistons. Some other changes came in the form of increased system pressure and a new fuel pump to match.
6.6L LML Duramax Engine
Improved Regeneration System for More Power
The LML Duramax changed some things in the regeneration system. To start, fuel sprays into the turbo downpipe instead of the cylinders during regeneration. This effectively eliminates the oil dilution problem. DEF is injected into the exhaust for reduced NOx emissions.
Thanks to the more efficient fuel burn, the regeneration cycles occurred less frequently, to the tune of every 600 or 700 miles. The previous LMM Duramax saw regeneration cycles occurring every 400 miles. This led to better fuel economy and power for the LML. In stock form, the LML had more power than previous engines and was capable of reaching up to 700 horsepower with modifications and tuning.
Stronger Block
The previous Duramax block was considered quite stout, however, the LML managed to improve on it with better casting and a revised main bearing profile. This resulted in an overall stronger block and improved oil flow. A higher-capacity oil pump was also added to keep everything lubricated.
Upgraded Rotating Assembly
The heads were left largely unchanged in the LML, but the rotating assembly was upgraded significantly to reduce weight. The lighter assembly wasn’t weaker; in fact, it was just the opposite. A trouble spot on the outgoing LMM Duramax was wrist pin bushings, so these were left out on the LML in favor of modified pins. The connecting rods were also made lighter, but they were still just as strong as the ones in the LMM engine. In other words, the LML Duramax featured a stronger and lighter rotating assembly.
New Bosch CP4.2 Injection Pump
A new Bosch CP4.2 injection pump was also added to the LML Duramax parts for this engine. This allowed for an increase in fuel pressure and resulted in a more efficient combustion process for more power and reduced emissions. Inside the turbo, a smaller compressor allowed it to function as an engine brake by cutting off exhaust flow. This improved the overall braking ability of the truck, but the downside was a less efficient turbo at higher boost levels. However, this negative effect isn’t really felt unless you’re pushing the engine over 500 horsepower with modifications.
Bosch CP4 Injection Pump
Common Problems with the LML Duramax
Like many engines, the LML Duramax suffered from a few common problems. In general, the trouble spots with modern Duramax engines are related to the emissions systems, and that is mostly the case here as well. However, there is one major and pervasive problem with this engine.
Fuel Injection Pump Failure
The biggest problem with the LML Duramax is the CP4.2 injection pump. It was built with a dual piston design and overly tight tolerances that led to it being very finicky and intolerant of dirty fuel. Naturally, diesel fuel is prone to becoming contaminated with water and grime, so it’s easy to see where this story ends. The CP4.2 injection pump was a failure waiting to happen, and many times it gave out after less than 100,000 miles.
The worst part about this failure is that it was often sudden, with almost no warning. Not only that, but replacing it was a pain because it involved replacing the injectors as well as the pump. This often adds up to a repair that costs around $10,000. The best way to prevent it from happening is to regularly change the fuel filter, ensure that you always use quality fuel, and/or install a CP3 retrofit kit.
Diesel Exhaust Fluid Heater Problems
If you live in a warm or mild climate where it rarely or never freezes, three heaters on the LML prevent DEF from freezing. However, consistent freezing temperatures taxed the heaters and made them more likely to fail. The popular solution that can’t be advocated due to legality is to simply bypass the system. Otherwise, it costs between $300 and $500 to replace a failed heater.
Bad DEF Pump
The DEF pump is similar to a fuel pump in a gas-powered vehicle, and it wears out rather quickly on the LML Duramax. There’s no clear reason why it fails in low-mileage vehicles, but it likely has something to do with dirty exhaust fluid. A failing pump won’t cause any engine damage, but it will trigger a warning light and affect drivability after about 200 miles. It’s not a particularly costly repair, with parts ranging between $400 and $500.
DEF Pump for Duramax LML
Reliability of the LML Duramax
Ultimately, the reliability of the LML Duramax has more to do with certain LML parts and not the actual motor. This has been a recurring theme in most Duramax engines since the advent of emissions control. The LML naturally has more emissions control diesel truck parts than the previous engine. On the previous LMM, the DPF and active regen were a problem. These parts don’t cause any additional problems on the LML. Further, they can be bypassed or removed, though the legality of that is questionable in most areas.
To sum up, the main problem with the LML Duramax is the CP4.2 injection pump, but that can be proactively replaced with LML performance parts. Otherwise, the LML Duramax is a reliable diesel engine that can go up to 400,000 miles if properly maintained.
Whether you have an LML Duramax or any other Duramax engine, you can rely on ProSource Diesel for upgrades and replacement diesel truck parts and kits.
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The post 2011-2016 6.6L LML Duramax Problems appeared first on Prosource Diesel.
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