These are different types of high-pressure fuel pumps used across various Cummins platforms. The CP3 is known for durability, the CP4 is a lighter, emission-focused design, and the HPI-TP is a unique twin-plunger pump used primarily on heavy-duty ISX/X15 engines.
The Details:
CP3 (Common Rail Pump): Found on many ISB (6.7L) and mid-range engines. It is a robust, externally lubricated pump (by engine oil or fuel). It is the preferred pump for high-horsepower modifications due to its reliability.
CP4 (Common Rail Pump): Introduced for tighter emissions standards and found on later model L9 and some X12 engines. It is smaller and more efficient but has earned a reputation for being susceptible to fuel contamination. Critical Note: The CP4 is "internally lubricated" by the fuel itself. If it fails, metal shavings often travel through the entire fuel system, destroying all injectors.
HPI-TP (High Pressure Injection-Twin Plunger): Used on the heavy-duty ISX15 and X15 platforms. It is a separate cam-driven pump capable of generating over 30,000 PSI. While durable, it requires precise timing and is driven by the engine gear train.