There's a setting change in the software to make the change to timing control.
When you change that value, you NEED to key off and wait ~60 seconds before keying back on.
Only THEN will it try to fire. I did the same thing you did after doing a full reset. The backfire didn't come from the fitech trying to fire though, but it was loud and scared me shitless.
I forget the name of the setting at the moment, but its in the instructions.
