air assist on the shocker is exhaust gasses.
the shots from a 1.9l 3000 psi is higher than bruce said, i get about 1300 shots. i did this last week and when i cam off the field i noticed that i only had about 150 psi left, lucky as i only had about 50 shots left.
also see if there is a crack or break in the firing piston, my cracked just after christmas and leaking gas and mis firing made me realise that some thing was wrong.