I removed my air pump a couple days ago and I sill have the stock main cat on. It's going to the garbage soon so don't start saying it will clog without the air pump etc

my problem is that now, untill I put my midpipe on, exhaust gases from the main cat comes all the way back into the air pump piping. Is it possible to make the ACV remain closed all the time? Sadly, unplugging it didn't work

 

there should be a split air pipe check valve



Other thing you could try is applying vacuum directly to the switching actuator to close off split air. The plugs on the ACV are for the bypass solenoids, those control pressure but they don't cut off flow.