Try disconnecting the vtec solenoid and measuring resistanec between the terminal in the plug (on the solenoid side) and body ground. Is there 14-30 ohms? If not then the solenoid is bad if there is 14-30 ohms the remove the solenoid and there is a filter between the VTEC solenoid valve and the cylinder head, check to see if this is clogged. If not then try pushing the plunger on the solenoid and see if the movement is free and that it does move. If all of this checks out then There must be some kind of problem between the ECu and the solenoid, I would take it to a shop if you really feel the VTEC is not functioning and the tests above check out.