No, I don't think bad gas will throw a CEL....but like I said, there might be a problem and you should find out what the ecu says is the problem. These things happen from time to time with parts.
I thank my lucky stars each time I start my car and arrive at the destination without something STRANGE happening. That's just me though. I'm always under the suspicion that something bad could happen cause I've almost died in the damn car, and that kind of makes a person paranoid.
You know what....don't listen to anything I said except to check for error codes.
To answer your question about the gas tank, I don't know about csm gas tanks that well. I did drain all the gas from a car once and there was a bolt on the bottom of the tank in the center which I took out to drain the gas.....and I've never been so high in my life!