Just another possible idea, check the fuel cap for a blockage or malfunction. As I understand the emission control requirements and fuel caps, the cap is basically a check valve designed to allow air to flow into the tank to replace the volume of fuel removed, but to block vapors from escaping into the atmosphere. I have had to replace three fuel caps over the years (not on crossfire) due to failing the local emission control checks required to renew the license plates. So if the cap is working properly, the tank can have a small pressure, but never a vacuum.

Just something to think about.