The LLY Duramax motor debuted in mid-2004 and continued through 2005 which was the shortest manufactured span of a version of the Duramax engine. The LLY was GM’s first attempt to implement the newly sanctioned emissions systems such as the Exhaust Gas Recirculation (EGR) system along with a catalytic converter. While adding these emission parts they also upgraded the turbo from the standard fixed vein turbo to the new Garrett Variable Geometry Turbo (VGT). This added features such as a turbo/exhaust break and allowed the factory to tune in their emission goals. GM also learned from the earlier injector issues on the LB7 and redesigned the valve covers so the injectors could have easier and quicker access which saved significant labor costs.
Some of the standard issues the LLY had were based off the newer upgraded parts. The factory turbo was upgraded in size so there ended up being a few air flow restrictions such as a small turbo inlet mouth pieces, restrictive intercooler pipes, and crushed downpipe which all created significant heat. The LLY only had an extra 5hp more than the LB7 but it had nearly 100lb-tq more than the earlier model which lead to transmission issues with the factory 5-speed Allison and its ability to hold that added power. A simple upgraded transmission rebuild kit fixed this issue. The LLY also utilizes a common rail injection system which ran into failure issues due to poor filtration. The factory fuel filter filters down through an 8-10 micron filter but the injector needs about 2 microns of filtration. These common injector failures can be fixed with simply installing an aftermarket Fass or AirDog Filtered lift pump system.