Charcoal can for emmissions usually has more lines on it, and at least one going to the carb area. I think Dave hit it with it being a vac res. canister. If you are running a Q-trac, you need it for shifting, jkas well as most of the other vac operated stuff. It just evens out the vaceum to a steady level.
1981 Cherokee W/T, 360, T-18, Warn 8274 in custom bumper/deer strainer (tested and approved)
1988 Cherokee 4 door, 3" Rancho lift, custom sliders/steps, custom roof rack, custom camo paint, custom camo headliner, custom bumpers and Warn 9500 HS, 31-10.50's
Only 31's, but can drag self with either rig
BLM John Day/Snake RAC-OHV Representative
Wolfpack 4x4's - Region 5 - "Cave Lupum"
VP- Outcast Land Use Review Team