Ford cheated on smog testing with a car that ran clean when the hood was lifted

 Cackette remembers one Ford that had a subtle switch triggered by opening the hood. The emissions controls worked when the hood was up, as it would be during a smog test, and not when it wasn’t.

https://www.hagerty.com/media/magazine-features/fifty-years-ago-the-government-decided-to-clean-up-car-exhaust-its-still-at-it/