yea i instaled headers on my 96 accord lx and a high flow cat and my cel light came on the code is po420 and problem says catalyst efficiency low bank 1 any ideas thanks....

 

The OBD2 system is insisting on the presense of the Secondary O2 sensor as well as the Primary O2 sensor. The Primary should be installed in the header collector, and the secondary in the outlet pipe of the converter.
it's either:
A Missing O2 Sensor
A Defective O2 Sensor
A harness / wire defect

 

While waiting for your answer I will throw in a little theory. If the primary O2 sensor is not reading the exhaust from all 4 cylinders (in the header collector) then the computer cannot properly compensate for poor emissions. If poor emissions get into the Cat, the emissions may be so bad that even a good Cat cannot clean them up. Thus the secondary O2 sensor will have too much activity and tell you that the Cat is not doing its job, which is a lie.

 

well im sure ur familiar with the non fouler the one i got the 02 sensor fits id say tight and id say there wouldent be enough air for it to be reading cause you look at it and it seems its suffocating it and my the second o2 sensor is brand new and is placed right before the flange at the end of the header and the first o2 sensor is at the top of the header i dno im going to try another non fouler that looks allitle bit different thanks...

 

You just answered your own question (or at least pointed it out).
The primary O2 Sensor goes where your secondary is mounted (end of the header and before the converter).
The secondary O2 Sensor is to be mounted AFTER the Catalytic Converter, preferably near the flange.
You may have to abandon the primary pipe mounting location and weld a mounting bung to the Converter outlet pipe for the secondary O2 sensor
Obviously, your OBD2 isn't going to be fooled.......

P

 

I would say that the first hole would be good for a extra setup to read exhaust gas temp, I have seen some aftermarket set ups for this, racers use exhaust gas temp readings to tune their engines but they normally get the temps from all four pipes.

Your setup is completely wrong my friend, this would not be a legal header in California and just does not work if you leave it like it is now. P Adams has the correct info.