The CP3 conversion on LML Duramax is one of the most impactful reliability and power mods available for the 2011-2016 trucks. It replaces the failure-prone CP4.2 injection pump with the proven CP3 design used on earlier Duramax engines.
WHY THE CP3 CONVERSION?
- The factory LML CP4 pump has a catastrophic failure mode that destroys the entire fuel system
- The CP3 (used on LB7 through LMM engines) is more durable and tolerant of US diesel’s lower lubricity
- A CP3 conversion eliminates the CP4 failure risk entirely
- With larger injectors and a tuned LML, the CP3 can support 700+ rwhp
WHAT’S INVOLVED
- Remove the factory CP4.2 pump
- Install a CP3 pump adapted to fit the LML’s fuel system
- Fleece Performance makes the most popular direct-fit conversion kit
- Requires a tune to adjust fuel trim tables for the CP3’s different delivery characteristics
- Add a FASS or AirDog lift pump — critical to ensure adequate CP3 inlet pressure
POWER POTENTIAL WITH CP3 CONVERSION
- Stock LML with CP3 + tune: 450–500 rwhp
- With upgraded injectors: 600–700 rwhp
- With compounds and built Allison: 900+ rwhp possible
FUEL SYSTEM PRECAUTIONS
- Always pair with a lift pump at 95 GPH minimum
- Use Stanadyne or similar lubricity additive at every fill
- Replace fuel filters more frequently after conversion