The LML Duramax (2011-2016) is a strong, capable engine whose main talking point is the fuel system. This complete guide covers the LML's key items and the parts that fix them, with links to the detailed guide for each.
CP4.2 high-pressure fuel pump
The LML switched to the CP4.2, which runs at tight tolerances and depends on fuel lubricity. A failure can send metal downstream to the injectors and rails, so clean, well-lubricated fuel at steady pressure is essential. Full guide: LML CP4 pump failure.
CP4.2 vs the earlier CP3
The LB7-LMM Duramax used the more forgiving CP3, while the LML uses the CP4.2. Understanding the difference helps you protect the LML pump. Full guide: the CP4.2 vs CP3 guide.
Protecting the LML fuel system
Keep the filters fresh, never run the tank to empty, address water intrusion, and consider a quality lift-pump setup and a lubricity additive. If a CP4.2 fails, a proper repair inspects and often replaces the contaminated injectors and lines, not just the pump.
Frequently asked questions
Is the LML CP4.2 a problem?
It works well when fed clean, well-lubricated fuel, but it is less tolerant than the CP3 of low lubricity, air, and water. Protect it with fuel quality and steady supply.
How do I protect my LML fuel pump?
Fresh filters, no running dry, added lubricity, steady supply, and prompt attention to water. Watch the fuel filter for debris.
The LML Duramax is a strong truck. Protect the CP4.2 with clean, well-lubricated fuel, and act immediately if you ever find metal in the filter.
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