CP4 pump failure, and what a DCR conversion does

The CP4 is the Bosch high-pressure fuel pump on a handful of late-model diesel pickups. It gets talked about a lot, mostly because of what happens when one fails.

Which trucks use the CP4

• 2011-and-newer Ford 6.7L Power Stroke
• 2011–2016 Duramax LML
• 2019–2020 Ram 6.7L Cummins

The 2017-and-newer L5P Duramax uses a different pump.

What a failure looks like

A failing CP4 can shed metal into the fuel. That debris travels downstream to the injectors, rails and lines, which is why the repair is rarely just a pump. Long cranking, a check-engine light, pump noise and lost power are the usual warning signs.

How often they fail

Less often than the forums make it sound. Ford's and Ram's recall filings each estimated that about 4% of the recalled trucks had a bad pump, so most CP4 pumps don't fail. Owners worry because of the size of the bill when one does.

What a conversion does

A conversion swaps the CP4 for a different pump design before a failure can happen. Depending on the truck, that means a DCR pump or a CP3-style pump.

Two things a conversion won't do:

• Save a pump that has already failed. Once there's debris in the system, the whole fuel system needs service.
• Add power. The truck makes the same power it did before.

Is it worth doing on your truck?

It depends on the miles, whether the truck is still under warranty, how hard you work it and how long you plan to keep it. A truck that tows every weekend and will be kept for years is a better candidate than one being traded next spring.

Check for open recalls first at nhtsa.gov/recalls. Ram's recall replaces the pump on some 2019–2020 trucks, and Ford's covers some 2020–2022 trucks with a software update. Recall work is free at the dealer.

Call with the year and engine and we'll tell you whether your truck has a CP4 and what a conversion involves on it. Conversions can often be scheduled for the same day, and DCR pumps carry the manufacturer's 2-⁠year, unlimited-⁠mile warranty.