Knock Sound

[85Silverado]

I'm hoping this isn't a Knock from the lower part of the engine. It's a bit deeper sounding then a lifter tap but not as deep as a few other knocks i've heard. But that could just be this one hasn't progressed that far. Would a dead cylinder make a knocking sound? I was getting a bit of backfiring and would smell lots of fuel from the exhaust and it wasn't running as smooth as usual. So I started pulling plug wires while she was running and after numerous shocks i finally came across a plug wire that didn't change the idle any when unplugged. It's not the wire cause it would spark to the frame....and my finger....so I'm thinking it's a dead plug. Would that make a knocking sound? Or is my engine dying? Thanks for any info.

P.S. Also checked around A.I.R. fittings and exhaust manifolds for leaks and have none

Paul D.
'85 Silverado