A faulty CP4 fuel injection pump in your LML 6.6L Duramax can lead to hard starts, excessive smoke, or poor fuel economy. When replacing bad CP4 pump, Look no further than the XDP Remanufactured CP4 Injection Pump. Each pump is assembled using the highest quality componentsand it built to meet or exceed the factory specifications. All pumps are end of line tested to ensure long service life and reliability.