Was at a PicnPull today and was looking at an EGR setup on a '93 California DOT truck -went back to my truck and noticed, no EGR as my truck was originally sold in Seattle. Yayyyyyyyy! EGR is usually one of the first things I service when I buy a used car here in California -my truck passed smog just fine!

 

Yes, the 4.0l OHV engines didn't get EGR Valves until 1995

They were lower emissions engines to begin with, 2.9l also didn't come with EGR systems in most places
4.0l and 2.9l used same block and design

Many Calif. sold vehicles had to have EGR systems when the other 49 states didn't require it.

EGR systems lower NOx levels when engine is under load.
NOx is a toxic gas produced during combustion, and its production spikes very high if cylinder temps get too high, which happens when engine is under load.
Adding exhaust gases to intake air slows the flame spread when the richer air/fuel ignites, this lowers the ignition temp in cylinder so lowers NOx production.

Beneficial side effect with EGR system is engine is less likely to ping/knock on lower octane fuel when accelerating, pinging/knocking is pre-ignition caused by rising cylinder temps pre-igniting the lower octane fuel.

Properly working EGR systems don't effect the power of engines, and on most they improve it if you run Regular gasoline(low octane).
Computer controlled spark systems can run a more aggressive spark timing for better power if EGR system is installed, no worry of pinging and knocking which robs power

But yes, they do tend to need servicing when they get older, exhaust systems are a rust making knuckle buster to deal with, lol.

 

Great information, thank you! One less thing to service, many folks have a way of ignoring EGR which leads to knuckle busting - I pull annually to clean and reinstall to ensure that I can install a new onion day if warranted.