need help on error code

[lulu44321]

hey guys i in a bit of a bind countless trips to autozone and with the code reader i get to codes a soft knock code and a fuel trim malfuinction change o2 with the universal type o i have an 95 240sx stock ka but a gutted cat anyways i get the code erased and not more then 5 hours later it comes back on but with no hesitation from the motor no knocking and under normal driving conditions please any help will be aperaciated

[lulu44321]

nobodys came into this problem before