Anybody ever have a major headache involving a 3rd generation Civic Si Oxygen sensor?

I need advice:

My PGMFI light is coming on - code 1 indicating bad O2 sensor. I installed a brand new NGK sensor but the light is still coming on. I didn't know what else to do so I took it to the shop and paid them $159 to tell me the O2 sensor was bad. They recommend installing a new "direct fit" Honda sensor and quoted me $340 for the part.

Just to make sure, i installed another new NGK sensor and it still didn't help.

Why aren't these new sensors solving the problem?
What could cause new sensors to go bad almost instantly?
My research is telling me that the original part IS an NGK. Is there any point in trying the factory part?

Any advice could save me a lot of money.

Thanks

code 1 is not necessarily bad O2 sensor, ( i am surprised the shop didn't tell you this) If your mixture is too rich or too lean you can get a code 1. Check the tailpipe, is there black carbon excessively, then its too rich. If you are getting normal MPG's i would just ignore the light, especially if there are no emissions regulations where you live. Trying to pinpoint why the mixture is not going to be worth it.

Thank you very much for the reply.

Yes, the car is running very rich - 22mpg, carbon at tailpipe, carbon on spark plugs.

I didn't know that the code 1 could just mean it is running rich;the manual doesn't even say that. What you are saying makes a lot of sense. So the O2 sensor is probably fine but what are the most likely causes for it running rich?

This all started immediately after putting in remanufactured fuel injectors. The tech at the shop said that if putting in a $340 O2 sensor didn't work then he would suspect the injectors because remanufactured injectors suck. Does that sound right? It runs really rough for a couple minutes after it has been sitting for a while. But the PGMfI light doesn't come on until I've been driving it for 10 minutes or so.