The truck shuts off at highway speed, cranks normally and refuses to restart. The fuel filter, when someone cuts it open, sparkles with fine metallic glitter. That’s the scenario CP4 owners dread, and it’s dreaded for a reason: when a CP4 high-pressure pump comes apart internally, the problem doesn’t stay inside the pump.
The metal it sheds is carried by the fuel to the rest of the high-pressure system, and on some layouts back toward the tank. A complete repair means dealing with everything that debris reached, not just bolting on a new pump.
Which trucks use the CP4
The Bosch CP4.2 is found on 2011–2016 Duramax LML and LGH engines, Ford 6.7 Power Stroke engines from 2011 on, and 2019–2020 Ram Heavy Duty pickups with the 6.7 Cummins. Confirm your pump from its label. For how the CP4 differs from the CP3 that preceded it, see Bosch CP3 vs CP4.
What’s happening inside the pump
A CP4 drives its pistons from a cam through roller tappets. The rollers depend on a film of fuel to roll smoothly. When that film fails, whether from water, air, poor lubricity or the wrong fuel, a roller can skid instead of rolling. Skidding steel on steel wears the cam and tappet fast, and the wear particles go wherever the fuel goes.
How it shows up
Some CP4 failures give warning. Others don’t.
- Gradual: low rail pressure codes such as P0087, especially under load; longer cranking; occasional loss of power
- Sudden: a stall or shutdown with no restart, often with rail pressure barely building during cranking
- Physical evidence: metal particles in the fuel filter, sometimes visible as a gray or glittery film
If you suspect a CP4 failure, stop cranking and stop driving. Each attempt circulates more debris.
What the debris can reach
| Component | Why it’s at risk |
|---|---|
| High-pressure pump | Source of the debris |
| Fuel rails | Collect particles that settle in the rail |
| High-pressure lines | Carry debris to each injector |
| Injectors | Fine particles lodge in the control valve and nozzle, where they can’t be reliably flushed out |
| Pressure sensors and relief valves | Mounted in the debris path |
| Return lines and cooler | Carry debris from injectors and pump |
| Tank, lift pump, filter housings | On some layouts, debris travels back toward the tank |
Engine manufacturers publish their own repair procedures for this situation, and contamination repair kits are offered for several of these engines. The common theme is that the high-pressure side is replaced, the low-pressure side is cleaned or replaced, and the tank is drained and cleaned. Cutting corners, such as reusing flushed injectors, rails or lines, or skipping the tank and supply-side cleaning, risks leftover debris damaging the new pump or the injectors.
Find the cause before the new pump goes in
A replacement pump can fail the same way if the conditions that caused the first failure are still there. Before reassembly:
- Sample the fuel from the tank and inspect the water separator.
- Check the low-pressure supply: lift pump pressure, suction restriction and air.
- Review fueling history: recent fill-ups, farm tanks, any chance of DEF or gasoline.
- Keep the evidence — the old pump, filters and a fuel sample — especially if warranty, an extended service plan or a fuel supplier may be involved.
If the cause was water, gasoline or DEF, read our guides to water in diesel fuel and DEF in the diesel tank.
Afterward: protect the new pump
- Buy fuel from high-turnover stations and avoid questionable bulk tanks.
- Change filters on schedule with parts that meet the engine maker’s specification.
- Drain the water separator and respond to water-in-fuel warnings immediately.
- Keep the tank from running very low.
- Consider whether a conversion or added protection is right for your truck, checking emissions legality and warranty implications first.
Further technical reference: Bosch Mobility: common-rail system overview. Use the exact engine/injector/pump service information for applicable procedures and limits.
Before you order parts, talk to DCT
Diesel Control Technicians works with major fuel-injection brands and can discuss supported CP4 component services by full part number. A contamination repair still needs the engine maker’s system-wide procedure. Send us the details of your failure — what happened, what was in the filter and what’s been done so far — and we’ll help you plan a repair that doesn’t leave debris behind. If you’re unsure which parts the debris reached, contact us before ordering anything.
Ask about pump or fuel-system service: Request a mail-in component review with the pump tag, engine application and diagnostic findings. Confirm supported testing or repair, intake terms and current timing. Local appointments: Hutchinson or Great Bend.