silver nipple, not sure if this thing is for vacuum or what. its located on the oil filler neck side on the iron. above rear rotor housing. ok go.

 

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Cap it. You don't need it if your emissions are removed. As long as the filler neck is running a PVC vent your fine.

 

that nipple goes to the charcoal canister. Should be a line on the firewall leading to the charcoal canister that is uncapped.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/tii-purge-valve-system-discussion-825093/ has a detailed discussion.

It doesn't really "go to" the charcoal canister. They are two separate systems whose outputs happen to be effectively tee'd together so they both discharge before the throttle plates. On the FD those two systems don't connect at all.

You can get away with capping it if you have the oil filler nipple either open, routed to a catch can, or routed to the TID/intake. But really, the nipple on the iron is an important vent for a turbo car due to the extra crankcase pressure turbo cars have. FD's only have one crankcase vent (on the oil filler) and they spew a ton of oil out during hard turns, so much that many people drill extra vents into the engine.

 

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