Why my truck doesnt p the smog check?

I have a 96 Ford F150 V8 5.8 Cyl 4X4 and even though I changed the air and oil filter, m air sensor, oxygen sensors, battery, spark plugs and cables, and added several STPS to the gas tank, it will not p the smog check. Also the check engine light is on so dont know what else to do?? I just changed the m air sensor and unplugged the negative in battery but check light came up again?? Any suggestions?? I dont have money for mechanic and dont mind getting greasy to fix it.. But lack knowledge..