Diesel Runaway
This is a diesel engine taking uncontrolled speed because it is fed from a source independent of the fuel system. Crankcase oil getting into the intake, or flammable vapours in the ambient air being drawn in, are typical causes. The engine does not stop even if the ignition is switched off, because what it is burning is no longer the fuel coming from the injection pump.
The critical feature of runaway is this: cutting the fuel is not enough. The fuel shut-off solenoid closes the injection line, but the engine keeps burning the oil vapour arriving with the intake air. Speed rises quickly, the engine runs on noisily and smokily, and it usually stops with mechanical damage.
The situations where the risk increases are well known: a leaking turbo seal, an overfilled crankcase, high crankcase pressure on worn engines, and operation in enclosed spaces containing flammable vapour.
The only proven solution is to physically close the intake path; this is done with an automatic air shut-off valve fitted to the intake manifold. This is a piece of equipment that must be planned separately in applications carrying a runaway risk.
Electronic throttle control is no remedy in this scenario. The GS740 and GS740-3P drive the position of the throttle lever; on a running-away engine, pulling the throttle lever to idle does not reduce the speed, because the fuel is not coming from there.
Context in which this term is used: Electronic speed and throttle control on a diesel engine