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I personally know of two incidents with runaway diesel engines. In both cases it was due to the operator inadvertently disabling the governor. The first one, which I didn't actually see, was a D4-U2 Cat. It wasn't pulling properly (or so my Dad thought), so he was fiddling with the injector pump rack while it was running. The rack came loose and all four injectors went to full on. The crew estimated that the engine reved to over 8000 rpm; this is an engine that spent its whole life below 2000 rpm. They tried to kill it by dumping the clutch: the clutch instantly disintegrated. I don't recall why the fuel shutoff didn't work, but they eventually killed it by crushing the fuel line (a 1/2" copper line). They probably would have tried to plug the intake, but the pre-cleaner was in the way. I helped to tear down this engine, and the internal damage was incredible: bent push rods, broken lifters, broken piston. In the second instance, I was one of the guilty parties. We had pulled an injector out of a Mercedes marine diesel and thought it would be a good idea to hit the starter to blow debris out ot the injector hole. These engines have a throttle body, and govern the engine at a constant manifold vacuum, a fact neither of us understood at the time. (Perkins diesels use a similar arrangement.) We had removed the throttle body, which meant there was, for all intents and purposes, no governor. Normally the Mercedes was hard to start, but it instantly fired up and reved up to several thousand rpm. We immediately closed off the fuel, but it took several minutes before it finally died. Surprisingly, the Mercedes ran fine after that for the next fifteen years until the boat ran aground in a hurricane and was holed. I've heard that it used to be common to have runaway diesels caused by cleaning the oil bath air cleaner with gasoline and not getting the bowl dry before adding oil.
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