they call that a runaway
about only a few things can cause it. It's getting artificial fuel, or runnin on it's own oil.
best way to shut one down is to cut off it's air supply, via your hand over the filter inlet, or collapse the rubber intake tube like what Iv'e had to do in the past.
something that always bothered me about more modern diesels. The epa doesn't like crankcase fumes to get into the atmosphere so most diesel engines re-route the crankcase vent back to the air intake, either pre-turbo on the forced induction engines or in the intake manifold on most of the naturally aspirated ones. But there's a problem with that. If for some reason the engine is overfilled with oil, or is rolled over, oil can enter the intake and due to the design of the engine it will run on it's own oil. Thus, say, you're mowing a hillside or whatever, tip the tractor over and you're throwed out of the seat. The bush hog blades are now capable of spinning mach jesus because the engine is running on it's own oil and will NOT shut off unless it's air supply is cut. Seat switch won't do a bit of good, key don't work, only thing that works is shutting off it's air or waiting til it runs out of it's "fuel" (or oil)...or the engine self-destructs. Whichever comes first.
I've seen it happen a few times, too. One was a loader operator that had the load way up the air and tumped the tractor on it's side (straight gear transmission), and it went into runaway, and just keps trying to run the guy over until it finally kicked rods out of the block and killed itself.
always hated that style CCV, needs a separator to keep oil out of the intake to prevent runaways.
