Chris_1

iTrader: (1)

I think they tend to seize up when they're really old. They can get rusty inside or otherwise compromised - they do have exhaust gas going through them.

AllFordsGuy

I agree that people fiddle with the emissions systems without knowing enough about them. I try to keep EGR working on all my vehicles. Like Chris_1 already said, it introduces exhaust gases to the combustion chamber. These inert gases essentially take up space and allow for less fuel to be used at cruising speed which can lower the production of NOx emissions because the combustion temperature is lower. The side benefit of this is the lower temperatures help prevent detonation. So if people do not have EGR, I typically recommend they use premium fuel because the higher octane makes it more resistant to early combustion (detonation). Although I do not know if detonation is an issue with these trucks.

Like Chris_1 said, you can put a vacuum to the actual EGR valve itself and see if you notice it open. If the vehicle is running, the idle should bog down and run rough when vacuum is applied to valve. If it does not, the EGR valve is not functional.