The Best Upgrades for Duramax LML Diesel Engines

The Duramax LML diesel engine continued the LBZ and LB7’s dynasty of power, but this new iteration boasted even greater capabilities thanks to technological advancements that had been made by the twenty-tens. Featured on 2011 to 2017 GMC Sierra HD and Chevy Silverados, the diesel engine met new emissions standards, came with higher payload and tow ratings, and had a state-of-the-art injection system.

The engine also came with even greater capabilities for drivers who modified it. If you’re currently driving one of these engines, here are the best upgrades for Duramax LML diesel engines.

Electric Lift Pump

The Duramax LML is the only Duramax diesel to ever require a lift pump. The well-established Bosch CP3 injection pump was changed out for a higher-pressure Bosch CP4.2 injection pump that met stricter emissions standards. Although GM never outfitted its 2011 to 2016 trucks with an electric lift pump, one should really be installed to keep the CP4.2 injection pump running well. An electric lift pump will help deliver a constant supply of fuel to the injection pump, thus keeping out any air that could cause problems with the injection pump’s tighter tolerances.

High-End Automatic Transmission

The 2011 to 2016 Silverados and Sierra HDs came with a well-built Allison automatic transmission, but even this has its upper limits. If other upgrades push the Duramax LML’s power above about 450 to 500 rwph, you’ll want to rebuild or replace this transmission to handle the high-end power output. Keep this in mind as you consider other upgrades, as they may only make sense if you’re prepared to invest in the transmission too.

Larger-Nozzle Fuel Injectors

To take full advantage of the Duramax LML’s capabilities, you need to get more fuel to the engine. That requires replacing the stock fuel injectors (which are prone to failure) with higher-calibrated aftermarket ones. Look for injectors that have larger nozzles so they can deliver the additional fuel that the engine needs.

Also, make sure to install that electric lift pump if you’re putting larger injectors in. The electric pump will ensure a sufficient amount of fuel gets to these nozzles.

Bigger Downpipe and Exhaust

If you’re upgrading the power at all, changes to the downpipe and exhaust should be made. Enlargen both of them — try a 3-inch downpipe and 4-inch exhaust — so they can usher away gases more quickly and keep the engine cooler. The downpipe is an easy part to change out when the transmission is already being worked on.