I have a goodman 100-4 rev8 and believe it was born in 1993. I have cleaned the flame tubes and replaced the flame senser and I have also bi-passed the rollout switch's trying to diagnose why it ignite's but will not stay fired.all my knowledge tells me it's a faulty safety issue.What am I missing and the code light is a continueous blink. Can someone help?

The furnace has a flame sensor (Repair Clinic # 2645136). It tells the control board if the burners lit.
If the burners do not lite, then check the igniter.

I can't find the blink codes in my Goodman manual but I believe a contstant blink to be reversed polarity but in reality it often indicates a bad board.