97 Ranger 4.0 check engine light, EVAP

My check engine light came on, and first it said EGR valve, so I replaced that.(I took it to Auto Zone to have the code read). It came back on 2 days later, and it still read EGR, so I replaced the DPFE valve. The light came on again and said EVAP, which Auto Zone said was a dealer item. I went ahead and replaced the EGR vacuum regulator solenoid, and again after two days the "check engine" light came on. What is it needing? What is EVAP? Is there a charcoal canister or something, I haven't found one.

Well, I changed the Canister Purge Solenoid, which plugs into the charcoal canister and has an electrical plug. The light hasn't come back on yet, so I think I got it. The part is a dealer only, and cost $62.00.