* Engine will likely not start. The fuel injectors are designed for the different viscosity and combustion properties of diesel fuel. Gasoline will not ignite properly in the compression ignition system of a diesel.
* Internal damage. Gasoline is a much more volatile fuel than diesel. It can damage seals and gaskets, and may dissolve some internal components.
* Fuel system contamination. The gasoline will contaminate the entire fuel system, requiring extensive cleaning or replacement of components including the fuel tank, fuel lines, fuel filter, and possibly the injectors and fuel pump.
* Catalyst damage (if equipped). If the vehicle has a diesel oxidation catalyst (DOC) or diesel particulate filter (DPF), gasoline can severely damage or destroy these components.
In short, putting gasoline in a 5.9 Cummins diesel is a very serious mistake that will result in expensive repairs. If you accidentally put gasoline in your diesel, do not attempt to start the engine. Instead, contact a roadside assistance service or a tow truck to have the vehicle towed to a qualified mechanic. They will need to drain the tank, flush the fuel system, and potentially replace damaged components.
