The LML Duramax (2011–2016, 6.6L) uses Bosch piezo injectors and the CP4.2 high-pressure pump. Most LML fuel-system trouble traces to one of these two — and the CP4 deserves special attention because its failure mode can affect the entire system.

Symptoms that point to the CP4 pump

• Sudden power loss, stalling, or no-start.
• Metal/glitter in the fuel filter — inspect immediately if suspected.
• Hard start and fuel-pressure fault codes.

If the CP4 has shed metal, expect a full fuel-system service (see our CP4 article) rather than a single part.

Symptoms that point to the injectors

• Rough idle, miss, or knock.
• White smoke and hard cold start.
• Reduced power and economy.

How to diagnose it

1. Inspect the fuel filter for metal first — this quickly separates a CP4 contamination event from an injector issue.
2. Pull injector balance/contribution data for cylinder-specific problems.
3. Check fuel-rail pressure against spec.
4. Confirm oil level/quality for injector-into-cylinder leakage.

Repair notes

Injectors are commonly done as a set. If a CP4 failure is confirmed, replacing only the pump risks the new injectors — plan for a complete service.

Before you order: LML injectors and pump components are application-specific. Verify the exact part by OEM cross-reference before purchasing.

See parts on our LML Duramax collection, fuel pump collection, and fuel injector catalog, or contact us with your engine details.