When I fire the Cordless nailer it makes a “POOF” sound. What is causing that?

This can be caused by several things, but a nail jam is the most common. Remove the fuel and battery then clear the jammed nail(s) from the tool. If the driver blade is in the down position the tool will not fire. With the fuel and battery removed from the tool, push the driver blade all the way up into the tool and test the tool.