have you tried a shot of starting fluid in the tb

 

If they are spraying in the run position, then that is where you're dropping pressure. They shouldn't spray if the key is just turned to "run" and not started. Once it's started, they will spray in the run position. I could be wrong on this, but I've never see a EFI engine that sprayed fuel until the command to "start" was given.

A simple check to see if it's the check valve is do key on, key off (no start) three or four times. If it fires right up on the third or fourth time, it's most likely the check valve. If it doesn't, I'd look somewhere else for the issue.