I've got a 2000 Explorer with a CEL and Check gas cap light. I replaced the Cap and solenoid valve. I reset the codes and they come back after a few driving cycles. I took the vehicle in for a smoke test and he said it was leaking at the solenoid I just replaced! He said it is probaly in the wiring.

What voltage should I have to close the solenoid?
What voltage should I have to open the solenoid?
What resistance should I across the solenoid coil?

Thank you in advance for your help. If I can't get it I am taking the vehicle back to the mechanic next weekend.