On my 78 there is a "stem" off of the valve cover that has a plug/cap on it. Its the oil fill tube but why is the cap connected to the bottom of the air filter? My car is in bad shape right now but everytime i stomp on the gas that cap POPS off the stem and smoke comes billowing out like the car is on fire. Me and my pops checked the compression and found the #4 has very low compared to the rest. Cracked piston ring?
That's a normal valve cover for a Turbo V6. It is a breather connected to the air cleaner for the PCV system. All engines use this. Just in the case, it looks odd becuase of the remote style air cleaner (instead of being on top of the carb like a NA engine).
Your bad cylinder is pressuring the crankcase and blowing the breather off.
Rich George
82 GN
83 T Type