The Bosch CP4.2 high-pressure fuel pump is used on the 2011+ 6.7L Power Stroke, 2011–2016 LML Duramax, and 2019+ Ram 6.7L Cummins. It builds the extreme pressure modern common-rail injectors need — but when it fails, it can send metal debris throughout the entire fuel system, not just stop pumping. Understanding the warning signs can save a much larger repair.

Why CP4 failure is different

When a CP4 wears or loses lubrication, internal components can score and shed metal. That debris travels downstream into the injectors, rails, and lines. The result is often a full fuel-system contamination event — pump, injectors, rails, and lines all need replacement — rather than a single part.

Warning signs

• Sudden loss of power, stalling, or a no-start with no prior warning.
• Hard starting or long crank times.
• Metal debris or glitter in the fuel filter — a key red flag; inspect the filter if you suspect trouble.
• Rough running or a check-engine light for fuel-pressure faults.

What to do

1. If you suspect failure, stop driving and inspect the fuel filter for metal. Continuing to run a failing CP4 spreads contamination.
2. Confirm fuel-rail pressure with a scan tool against spec.
3. If contamination is confirmed, the accepted fix is a complete fuel-system service. Replacing only the pump risks leftover debris taking out the new parts.

Prevention

Owners commonly reduce risk with diesel fuel lubricity additives and, in some cases, "disaster-prevention" kits or CP3 conversions. These are application-specific — verify compatibility before buying.

Before you order: CP4 components and contamination kits vary by platform and year. Verify the exact parts by OEM cross-reference for your vehicle.

See high-pressure pumps in our fuel pump collection and prevention/repair options in our fuel contamination kits, or contact us with your engine details.