P0440 help 01 Z28

[Corvettejon]

Here's what I have so far:
1. new gas cap.
2. code cleared (removed fuses).
3. code returned.
4. intermittent, inability to fuel car (gas just sprays back out).
5. removed gas filler neck, pushed on check valve, pressure released from tank.
6. now able to fill car with gas.

Appears that pressure in gas tank is keeping check valve sealed even when car is off. I would assume that the Evap. Canister or its vacuum lines are the culprit.

Suggestions on which to check first.

[mrr23]

the EVAP canister could be bad.