hvsds-
Runaway diesel isn’t the same thing. That’s often due to unwanted fuel or oil getting into the cylinders which causes the engine to run away. It’ll often only stop once it’s consumed all the oil in the sump.
The black smoke is a fundamental issue with diesel combustion. Low cylinder pressures and low (relatively) injector pressure causes that black smoke. Because the combustion is so incomplete, a lot of air gets out unused, so those diesel tuners simply pump more fuel in until all the air gets used and that gives them their maximum power. The result is all that black smoke.
Auto manufacturers started getting round this in the early 00s by significantly increasing the cylinder and injection pressures and injection timing. That increased the fuel efficiency somewhat and stopped most of the black smoke, but forced the particulate size smaller. PM10 became PM5, and now PM2.5 and smaller, which is basically nanoscale particulate and quite carcinogenic because it readily passes through cell walls.
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Jonny69
Someone in the comments was saying those things have so much power that they burn a crazy amount of fuel and it’s not physically possible to suck enough air into the engine to match the fuelling so a lot comes out the stacks.
I don’t know why they don’t turn down the fuelling in that case, I don’t know much about engines, let alone diesel truck engines.