98C cocking problem

Marker setup:  98 Custom, Dye Excel barrel, Empire Reloader II, Tippmann expansion chamber, Rocket Cock, 32 degrees Star Fire bolt, Dark Horizons Titanium Hammer, 16oz and 20oz CO2 tanks.  My problem:  I have never had any problems from my marker until recently. Last time I went out to my local field I went to chrono and after about the third shot I could hear a hissing from inside the gun.  Tried shooting a few more times and the hissing continued.  My buddies said I had a cracked power tube, so I used one of my friend's backup gun for the day.  Got home and disassembled the gun and could find no crack in the power tube and no obvious problems.  When I went to test it, it would fire once or twice normally, then either fire like the tank was empty (rapid cycle) or just dead, like no tank attached.  Recock the gun & try again - same results.  Took it apart again & cleaned & oiled everything and got my tanks refilled just to make sure.  Tried testing again with the same results.  I could fire as many as 20 - 30 shots without having to recock or I might have to recock after every shot.

My money is with Monk and Bruce .

The most likely cause is a piece of debris inside your CVX valve (power valve) , maybe even a bit of the sealant from where the hose screws in may have dislodged and caused your problems .