It might be worth looking a little closer at the cams too. Not sure how far you went in decommissioning them and their associated wiring. Here's a couple shots of my PRR L1s. I'm pretty sure they are just using the selector switch in series with one of the switches to disable it for 2 chuffs. The cams are 90deg out of phase so when they are both enabled you get your 4 chuffs. They are adjustable with tiny setscrews so I would check to see if one or both slipped out of phase and/or lateral alignment. Changing the chuff select may yield a clue. If yours was connected to the CC board, then this circuit grounds the chuff input. They may have picked up ground anywhere along the way or ran the wire back to one of the CC's common connections.
Nice thing about this setup - it gives a solid 4 chuffs when in working order without extra hardware. It can also be phased to match crankpin angle if you're insane about that stuff like I am. 
