got a jdm p73 with my b18c spec r, and passed everything except HC tailpipe test,
any thoughts on what could be wrong?

 

sounds like your ecm its jdm u said right, also have you given it a tune up sparkplugs and also check that your gas cap is good , also ur cat and before you go retest drive the car for about a hour before testing i have a friend that has given me some tips when going too get smogged doesnt hurt too try,also when pulling out the plugs keep them in order and look at each one and youll see if there is any issues with each cylinder.

 

if this is still an issue advancing the timing can give lower hc readings but will raise co so depending on the readings there is room for adjustment. and also leaning out the fuel ratio

 

so first things first, i should check my spark plugs