Bingo. YES You got it. I lost power and I hear it hissing.. ThanksThermactor crossover tube.
The hose runs from the air pump located below the alternator to that pipe, which pumps air into the heads with the goal of helping the pre-cats acheive max efficiency during vehicle warmup. When the car is warm, the air is routed own to the H-pipe to feed those cats.
If you have no converters on the car, you can pull this all off and block the ports on the heads.
This is the part
79-93 Mustang thermactor head tube pipe w/ valve | eBay
We do not, have not and will not ever part out a good car.www.ebay.com
Far from easy due to all the carbon build up on the threads. It's far easier to use the block off plates that LMR sells.They make allen key plugs if you pull it off, i just can't remember how easy it is do with the heads on the car.