Though not the first electrically controlled diesel in the light-duty market (the Ford 7.3L Power Stroke was), the General Motors 6.6L Duramax is recognized as one of the most sophisticated. It boasts four-valve aluminum cylinder heads, excellent component packaging, and a reputation for durability, power, fuel economy, low combustion noise, and very little vibration. Ironically, this high-tech engine exists due to the government-mandated emissions standards that required a 90-percent reduction in tailpipe discharge from previous mechanically fueled designs. Thus, gasoline-style engine management was required to tame and improve upon the diesel engine.
The Diesel Combustion Challenge
There are three basic stages of diesel combustion that take place inside a direct-injection diesel engine-delay, uncontrolled combustion, and controlled combustion. These three stages are defined as follows:
The '06-and-newer injector...
The '06-and-newer injector quantity adjustment (IQA) injectors are flow-matched to the engine calibration software for variations at different duty-cycles. By doing this, the injectors are matched to the engine and the engine control module calibration.
Delay: Diesel fuel is sprayed into the compressed air charge in the cylinder and waits for the temperature to reach 1,000 degrees F to ignite.
Uncontrolled combustion: The injected diesel fuel then burns very rapidly in a rogue manner, much like detonation in a gasoline engine. This creates the diesel clatter.
Controlled combustion: The additional diesel fuel burns at the rate it is injected into the cylinder.
High-Tech Duramax Solution
To achieve the desired emissions, noise, and vibration goals, the uncontrolled combustion stage needed to be minimized or eliminated. This could only be done through electronic control of the injector and an extremely high-pressure fuel source. In the case of the Duramax, GM uses a Bosch common-rail fuel system. The intent was to eliminate or at least minimize the central core of a mechanical injector spray pattern that would evoke the uncontrolled combustion event until a reaction zone (where the heat from the burned fuel travels into the unburned fuel) could be established.
Recognizing the need for the enthusiast to understand how electronic common-rail diesel engines operate, Diesel Power attended the General Motors Training Center in Ardsley, New York, to learn about the Duramax diesel engine. Special thanks to Training Center Manager Anthony Levens and Duramax instructor Don Post for making our hands-on education possible.
The Four Different Duramax Engines
The Duramax 6600 has been produced in four different versions, and each version gets its name from its engine code. These engines are commonly known as the LB7, LLY, LBZ, and LMM. The engine models break down by the following codes, model years, and VIN numerals:
LB7- 2001 to 2004, VIN code 1
LLY- 2004.5 to 2006, VIN code 2
LBZ- 2006 to 2007, VIN code D
LMM- 2007.5-present, VIN code 6
Though there were evolutionary changes over the years to the engine and controls, most basic component functions stayed the same. The notable updates came when GM switched to the LLY engine in 2004 1/2 and added a variable geometry turbocharger, EGR, and altered the cylinder head and injector design. Then came the LBZ in 2006 and it featured a lower compression ratio, higher injection pressure, and an improved engine block design. The LMM version that arrived in 20071/2 added an electrically controlled throttle body that works in conjunction with the EGR and diesel particulate filter (DPF) to evoke the regeneration/cleaning process.