If you own a modern common-rail diesel, you've probably heard of the Bosch CP3 and CP4 high-pressure fuel pumps. They do the same job — generate the high pressure that feeds the injectors — but they have very different reputations. Here's the practical difference.

The CP3

The CP3 has been used across many diesel platforms (including the 2003–2007 5.9L and 2007.5–2018 6.7L Cummins, and the LB7–LMM Duramax). It's widely regarded as robust and forgiving, which is why it has a strong track record.

The CP4

The CP4.2 is newer, lighter, and more efficient — used on the 2011+ 6.7L Power Stroke, 2011–2016 LML Duramax, and 2019+ 6.7L Ram. Its weakness is lubrication sensitivity: under certain conditions it can score internally and shed metal throughout the fuel system, turning a pump failure into a full-system replacement.

Failure signs to watch (CP4)

• Sudden power loss, stalling, or no-start.
• Metal/glitter in the fuel filter.
• Hard starting and fuel-pressure codes.

Your options

• Fuel lubricity additives to reduce wear risk.
• Disaster-prevention kits that bypass debris.
• CP3 conversion kits that replace the CP4 with the more robust CP3 (popular on the affected platforms).

All of these are application-specific — verify compatibility for your exact platform and year before buying, and confirm parts by OEM cross-reference.

Browse high-pressure pumps and kits in our fuel injection pump collection and fuel contamination kits, or contact us with your engine details for guidance.