Each cylinder of the CP4.2 features a piston assembly, plunger, spring and head. Bosch CP4.2: The Past, Present and Future High-Pressure Common-Rail Pumpīosch’s CP4.2 is the twin piston high-pressure variant in its CP4 pump line (the CP4.1 is the single piston version, employed overseas in various diesel engines). Below, we’ll explain why the CP4.2 fails, show you what it looks like when it self-destructs and then lay out how you can keep this failure from happening to you. Luckily, the addition of an aftermarket electric lift pump can help ensure that positive pressure (and no air) is supplied to the low-pressure side of the CP4.2-and can be installed relatively affordably. The LML Duramax doesn’t have a factory lift pump. The primary reason for this is the fact that the Power Stroke comes factory with an electric lift pump feeding it consistent low-pressure fuel supply. One engine that is exceptionally susceptible to CP4.2 pump failure is the LML Duramax, the 6.6L diesel V-8 GM offered in its ’11-’16 model year HD trucks.Īlthough Ford’s 6.7L Power Stroke utilizes a very similar version of the CP4.2, it’s proven much more reliable in ’11-present Super Duty applications. Unfortunately, the CP4.2 has a fatal flaw that can spell disaster for not only the pump itself, but the rest of the injection system and possibly even the engine. This means diesel engine manufacturers can meet extremely stringent particulate matter emission standards while keeping the overall production costs of their engines down. It costs less for the manufacturer to produce yet produces much higher injection pressures than its predecessors. The Bosch CP4.2 represents the evolution of high-pressure diesel fuel pump technology.