Honda Civic Forum - vtec/o2 sensor question

:_doh:hey guys and gals, im kinda new to honda but im having an issue with my car and for the life of me cant figure it out. first i will tell you what i have.
i have a 96 coupe 5 speed, its got a D15B motor. the computer is the stock 96 5 speed. it apears to have all the stock wiring. the check engine light is on due to the code for the o2 sensor. it only has one in it below the header, cant locate a pigtail for the lower one even though the 96 should have one... when i got the car it was having a cooling issue turned out to be the radiator, got that all fixed. but because im shipping this to germany to be safe we changed everything, water pump, hoses, radiator, thermostat and we changed the head gasket.
now my problem, before all this even with the CEL on and overheating the vtec worked perfectly. upon reassymbly i have no vtec. ive ran through all the tests, the solenoid clicks when power is applied, oil level is perfect, operating temp is fine,i cleaned the screen and the solenoid itself and checked for blockage and free movement of the piston inside of it....i have no clue why after removing the head it wont work. i compaired the gaskets and they were the same, as the parts store showed the same part number for the d15 as the d16 original motor. what else could i be missing? could it finaly just need to have the o2 sensor addressed? also when i got the car it had no cats and no simulators, but like i said the vtec worked, i have sence added a cat and cleaned the upper o2 sensor but the CEL is still on and i have no clue, i ran out of time before having to ship the car so im trying to get ideas and maybe parts together before i meet up with my car in 2 weeks so i can fix it. any help? thanks in advance!