2007 subaru impreza 2.5i MISFIRE

I have a constant misfire in all my cylinders when i plug my code reader. i
have changed distributor,spark plugs,spark plug wires. The basic stuff for
misfire now some backstory about it I head people say it was a fuel injector
or a bad ecu. the reason being a fuel injector is because when i went to utah
i use there gas and for some reason the check engine light was gone and
then when i drove to back to las vegas and refilled at my gas station the
check engine light comes back. the reason for ecu is because i go to
autozone and the code reader does not work but at oreilly it does autozone
said it was my ecu but i head that is really rare please help!