Tom Zeller & Norman Mayersohn:

In a testing cell tucked deep in the bowels of Navistar’s engine plant and technical center here, a hulking prototype of a truck engine sits behind a large glass window like a patient on an operating table. A snarl of sensors and wires is attached to nearly every part of the humming engine, feeding reams of data to a battery of computers and watchful engineers in the adjacent control room.
One measurement — for nitrogen oxide emissions, or NOx — is of particular concern to Navistar. From 2010 onward, all new truck engines must achieve tough, near-zero limits for NOx, a chief ingredient of smog. Virtually every truck maker besides Navistar chose to use an add-on system to their existing engines that uses a fluid cocktail to help neutralize the pollutant as it makes its way out of the exhaust.
Navistar went a different route, deciding to invest hundreds of millions of dollars to refine an engine that produces minimal NOx in the first place. At the same time, the company attacked the competing systems, suing federal air quality regulators and claiming that the add-on technology was so flawed that it failed to meet the clean-air requirements.