Original article by Aaron Brzozowski for GM Authority Oct 18, 2018: http://gmauthority.com/blog/2018/10/why-some-gm-exhaust-tips-become-blackened-with-use/ As governments around the world continue to ratchet up the pressure on automakers to produce ever more fuel-efficient automobiles, direct injection has gone mainstream. That’s where fuel is injected directly into the cylinder, rather than being sprayed in…