getting CEL warnings after recently fitting new O2 sensors and Eurocup GT cats so Im thinking I need to fit some extenders to the sensors.
Do I need to fit extenders to all 4 sensors or only the two post cat sensors?:

 

Just the post two cat sensors. I bought mine from pep boys. they're the 18mm ones and I think its was less then $5 for the pair.

 

thanks

 

They're actually called spark plug anti-fouler. If you go in there and ask for a sensor extender they will just stare at you with a stupid face and ask you ten million questions as what you actually want to do and why.