There's Volkswagen, that had diesel engines that could detect when they were being tested and changed the performance to improve results. These engines emitted nitrogen oxide pollutants up to 40 times above what is allowed.

And there's there's this. This is INSANE if you ask me. It's modifying a diesel engine where the sole purpose is to emit an excessive amount of black smoke. It's a form of 'f*ck you anti-environmentalism.