My hitachi nv45ab2 roofing coil nailer misfires and only shoots every third nail

Hitachi coil roofing nailer will skip nails if the piston oring is worn, the feed spring is weak or lower bumper is cracked. Easy to check. Remove nails and air supply. With side door open point nose of gun up then down again. If the piston moves up and down in the cylinder, replace the piston oring. If piston does not move and is in the up position, check the feed spring for tension. With air supply removed and door open, slide feeder back and press on feeder from door side to check tension. It should spring back to position against rails.If is feels loose, replace spring and retainer pin if the pin is worn. If piston oring is good, and the feeder has good spring tension, suspect lower bumper and the plastic part below the bumper called the "sheet". Remove head and pull the cylinder to examine lower bumper. Parts are available at www.toolpartsdirect.com. Good luck with your repair

Feeder spring broken , missing , worn. also check to make sure the tip of the driver is flat, it will look rounded if it is worn

Very common problem usually solved by a new feed spring. Also inspect the two small "ears" on the feeder where the legs of the spring go as they can break off.