I have a question about how an EGR valve functions. I'm trying to diagnose the valve on my 87 Ranger. When I apply vacuum to the valve I can see the diaphram pucker up a bit, but I see no other movement. In the inlet that connects to the exhaust pipe there is a valve that is recessed about a third of an inch. When vacuum is applied and the diaphram moves, shouldn't that valve move also? Mine doesn't, it just sits in the same spot when vacuum is applied and when it is let off. Does this mean that the valve is defective? Also, should that valve in there be recessed, or is it stuck open a bit?

 

It might just be stuck in its seat. It isn't at all unusual for carbon to build up inside those things and have them plug up. If you don't need it for emissions and the engine isn't pinging (EGR gasses cools combusion, which allows the computer to run more timing, hence why some vehicles ping when the EGR isn't operating) I'd just leave it be. You can try cleaning it out if you wish.