Possibley alternator?

I have a 1989 camaro RS that i bought last summer. The car was stored for a couple years and has never seen winter. Last fall and still this spring the service engine soon light starts flashing occasionally. I ran the car for codes 3 different times with a diognostics machine but nothing ever came up. I replaced plugs, wires, cap and rotor, and the fuel filter. I actually changed the fuel filter 2 or 3 times, after everytime i did it the car was fine for awhile. I don't know if it was a coincidence or if i just have a bunch of crap in my gas tank that is plugging my injectors. I was just wondering if any of you guys out there have had any similar problems and if so, if it could be the alternator.
Thanks alot,
Chris

check your oxygen sensors

read the codes when the check engine light is on

already replaced the O2 sensor and no codes come up