Originally Posted by
big john
They've been in use for almost 50 years. Some are very simple things and many cars don't have them because their NOx emissions are low enough. Some engines use valve overlap to introduce exhaust gas to the intake instead of using an EGR valve.
Some are quite complex and cause headaches for technicians.
Took me a minute to wrap my head around Toyota.
Ford started using EGR valves as much to reduce pumping losses as NOx reduction.