Hello and thank you for your question.
Firstly make sure you pressure gauge on your air compressor is turned up enough for your brad nailer. I had a problem with my finish nailer and found after some investigating that my pressure was way to low for the nailer.
Secondly make sure the brads you are using are recommended for your nailer.
Lastly if those are not the issue I would guess that you have a busted seal or o-ring. and the maintenance kit is the way to go here is a schematic for your nail gun to help you replace the busted seal
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Thank you for your answers. So far I have disassembled the nailer, cleaned the inside parts (not overly dirty), relubricated all of the parts with appropriate lubricants and carefully reassembled the gun. The "O" rings have a slight amount of wear on them but are not worn out or broken as I always oil the gun before and after using. The nails are the porter-Cable 18 ga. that I use. My air hose stays coiled in a holder when not in use. I also checked the pressure on my compressor, it was about 110 which is where I usually run it for this nailer.
Thanks for the suggestions, though. Do you have any other ideas?