Could be the same problem I had: AKA Solenoid blown, tips to fix?
One way to find out is to remove the grip frame, and air up the marker slowly (so you only hear a small leak). Use your fingers or a few drop of oil and feel around the solenoid (or check for little bubbles in the oil) to see if you feel anything. If you do, then it's likely either the solenoid or the o-rings between it and the body. Good luck, let us know what you find out!