Brian Barton
The Duramax V8 engine is a family of 6.6-liter diesel engines produced by DMAX, a subsidiary of General Motors. The LB7, introduced in 2001, was the original Duramax engine and did not include emission control devices. The LBZ, introduced in 2006, was the last generation of Duramax without emissions control parts. The LMM engine, introduced in 2011, marked the emissions era of Duramax engines and included several new emissions control devices, such as a diesel particulate filter (DPF) and an oxidation catalyst. The L5D engine, introduced in 2018, includes advanced emissions after-treatment systems, enabling it to meet stringent EPA and CARB emissions standards. While the inclusion of pollution control devices in Duramax engines has helped reduce emissions, there have been lawsuits against General Motors alleging the use of emissions-cheating devices in some Duramax Diesel trucks.
| Characteristics | Values |
|---|---|
| Duramax engine family | LB7, LLY, LBZ, LMM, LML, L5P, L5D |
| LB7 engine | Does not have emission control devices |
| LMM engine | Includes emission control devices such as a diesel particulate filter (DPF), an oxidation catalyst, and an EGR |
| LML engine | Includes emission control technology such as Selective Catalytic Reduction (SCR) and a dual-loop EGR system |
| L5D engine | Includes advanced emissions after-treatment systems |
| Emissions-cheating devices | Used in 2011-2016 Chevy Silverado and GMC Sierra Duramax Diesel HD vehicles |
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What You'll Learn
LB7 engines without emission control devices
The LB7 is the original Duramax engine, introduced in 2001. It is a first-generation model known for its strong performance. However, unlike the LB7 engines sold in California, this model did not include emission control devices, which contributed to its reliability. The LB7's lack of emission control hardware makes it a popular engine for diesel fans as emissions technologies such as exhaust gas recirculation (EGR) can affect power output and fuel economy.
The LB7 engine has a long lifespan and reliability, and its simple design makes it a favourite among diesel enthusiasts. It is also sought after due to its injector issues, which are its only weak point. The injectors are prone to cracking and failing past the 100,000-mile mark, requiring costly replacement parts and labour. However, with good maintenance and improved injectors from Bosch, many owners still appreciate the LB7's simplicity and performance.
The LB7 is a good choice for budget buyers as it is a dependable, first-generation engine. Diesel Direct Fuel Injection was introduced with this model, so it is not yet perfect, and fuel injector replacements are often necessary. However, most of the old issues with the LB7 can be resolved by installing modern Duramax diesel parts, and any weak or failing parts have likely already been replaced.
The LB7 is highly sought after, with strong aftermarket support and tuning potential. This provides ample opportunity for performance upgrades, making it a popular choice for those looking to modify their vehicles. Despite its injector issues, the LB7 is still considered one of the most reliable Duramax engines, especially for enthusiasts who don't mind injector replacements.
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LMM engines with emission control devices
The LMM Duramax engine is a 6.6L diesel engine produced by DMAX, a subsidiary of General Motors, and was offered for model years 2007–2010. The LMM engine was introduced in response to a 2007 EPA mandate that extended emissions requirements to diesel engines used in light trucks.
To comply with these new regulations, the LMM Duramax engine was fitted with new emissions control devices, including:
- A diesel particulate filter (DPF) that traps and burns off excess particulate matter (soot) through passive and active regeneration.
- An intake airflow valve that restricts the amount of incoming air, allowing the engine to maintain sufficient heat and control combustion temperature more precisely.
- A larger exhaust gas recirculation valve (EGR) that helps to reduce nitrogen oxides and improve engine efficiency.
- A diesel oxidation catalyst that reduces soot and particulate matter.
While these emissions control devices significantly reduced the level of contaminants released into the air, they also impacted the LMM engine's fuel economy, reliability, and longevity. For example, the active regeneration process of the DPF required the addition of extra fuel, which reduced the overall fuel economy of the engine.
The LMM engine was succeeded by the LML engine in 2011, which featured further improvements to comply with federal emissions standards and enhance durability.
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L5D engines with advanced emissions after-treatment systems
The L5D Duramax diesel engine is a 6.6-liter V8 engine designed for medium-duty applications, such as GM's Chevrolet Silverado 4500HD, 5500HD, and 6500HD trucks. It offers a balance of performance and efficiency, producing approximately 350 horsepower and 700 lb-ft of torque. The engine features a variable-geometry turbocharger, which enhances its performance and responsiveness across a wide range of operating conditions.
The L5D engine includes advanced emissions after-treatment systems, enabling it to meet stringent EPA and CARB emissions standards. These after-treatment systems are essential for removing pollutants from diesel engine exhaust. The L5D's specific after-treatment technology is not publicly available, but several advanced technologies are commonly used in diesel engines to reduce emissions.
One such technology is the diesel particulate filter (DPF), which captures and stores exhaust soot to reduce emissions. The DPF is combined with other technologies, such as oxidation catalysts, to further enhance its effectiveness. Another technology is selective catalytic reduction (SCR), which uses a catalyst to convert harmful pollutants like NOx into harmless compounds like nitrogen and water.
The L5D engine's advanced emissions after-treatment systems are tailored for durability and reliability, making it well-suited for demanding commercial and fleet operations. These systems are designed to meet stringent emissions regulations and improve air quality, protecting human health and the environment.
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LML engines meeting Tier 2 anti-pollution standards
The 6.6L RPO LML (VIN code "8") is the 2011–2016 version of the Isuzu/GM Duramax V8 diesel engine. The LML engine was significantly updated for 2011 to comply with the new federal emissions standards for diesel engines, provide better engine rigidity, and further reduce noise. The engine gained new 29,000 PSI piezo injectors, a completely reworked fuel system, and a urea injection to reduce nitrogen oxides. The LML engine also meets the stringent Tier 2 anti-pollution standards.
Tier 2 vehicles are those that meet the requirements of one of the available bins and are used to meet the requirement that a percentage of the fleet has average NOx emissions of 0.07 g/mile. The emission standards for all pollutants (certification bins) are shown when tested on the Federal Test Procedure (FTP). The LML engine's emissions controls include selective catalytic reduction (SCR), a downstream fuel injector (ninth injector) for diesel exhaust fluid (DEF), a diesel particulate filter (DPF), exhaust gas recirculation (EGR) with dual EGR coolers and an EGR cooler bypass circuit, and a diesel oxidation catalyst (DOC).
The LML engine's use of a Bosch CP4.2 fuel injection pump, which draws fuel from the new 36-gallon fuel tank, plays a crucial role in improving emissions performance. The CP4.2 pump squeezes diesel up to 30,000 psi (2,000 bar) out to the engine's piezo-actuated fuel-injection system, allowing the LML to run on ASTM grade B20 biodiesel while ensuring more precise fuel delivery. The LML also utilizes a Honeywell AVNT (Garrett GT3788VA) Variable Vane Turbo (VVT) that helps give the Gen 4 GM V-8 diesel its improved power and fuel economy while lowering exhaust emissions.
The LML Duramax is a significant improvement over its predecessor, the LMM, which marked the emissions era of Duramax engines. The LML boasts an 11-percent increase in fuel economy and offers 397 hp and 765 lb-ft of torque, surpassing the LMM's performance. The LML also abandoned the previous generation's high-pressure fuel pump to support its emissions control. The LML's emissions control devices, such as the DPF and EGR, can impact fuel economy and reliability, but they are essential for meeting modern emissions standards.
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Duramax engines with emissions-cheating devices
The LB7 Duramax, first introduced in 2001, is an early-2000s diesel engine that does not have any emissions control hardware. This makes it a popular engine for diesel enthusiasts as emissions technologies such as exhaust gas recirculation (EGR) can affect power output and fuel economy. The LBZ, introduced in 2006, is also sought after for the same reason.
However, the LMM marked the emissions era of Duramax engines. This engine includes several new emissions control devices, including a diesel particulate filter (DPF), an oxidation catalyst, and a new EGR. The L5D Duramax diesel engine, a 6.6-liter V8, also includes advanced emissions after-treatment systems, enabling it to meet stringent EPA and CARB emissions standards.
In 2017, a class-action lawsuit was filed against General Motors, alleging that the 2011-2016 Chevrolet HD and GMC HD trucks with Duramax diesel engines were equipped with "defeat devices" to skirt federal emissions standards. The lawsuit claimed that these trucks produced two to five times the legally allowed amount of emissions and that GM had secretly installed software to cheat on emissions tests to boost sales. The lawsuit specifically targeted the LML Duramax engine, which was offered in the 2011-2016 Chevrolet Silverado and GMC Sierra HD pickups.
General Motors denied these allegations, stating that the Duramax Diesel Chevrolet Silverado and GMC Sierra complied with all U.S. EPA and CARB emissions regulations. They planned to defend themselves in court against the accusations.
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Frequently asked questions
Pollution control devices are mechanisms that help to reduce the emission of harmful pollutants from vehicles. These devices are designed to limit the release of pollutants such as nitrogen oxides (NOx) into the atmosphere.
The LMM Duramax engine, introduced in 2007, was the first Duramax engine to feature pollution control devices, including a diesel particulate filter (DPF) and an oxidation catalyst. The LML Duramax engine, available from 2011 to 2016, also featured advanced emission control technology, meeting stringent Tier 2 anti-pollution standards.
Yes, the LB7 and LLY Duramax engines, introduced in 2001 and 2004 respectively, did not include emission control devices. The LBZ engine, introduced in 2006, was the last generation of Duramax engines without emissions control parts.
There have been some reported issues with the pollution control devices on certain Duramax Diesel models. For example, the LMM engine experienced reduced fuel economy due to the introduction of the DPF, and some owners have removed the DPF and EGR systems to improve reliability. Additionally, there have been lawsuits against General Motors alleging that certain 2011-2016 Duramax Diesel models were equipped with emissions-cheating devices, resulting in higher-than-expected levels of NOx emissions.
