I've recently been throwing a CEL#1 (which is a primary O2 sensor) on my 00 GSR. I'm running a OBD1 P28 chipped ecu. I recently swapped out the stock header, cat and exhaust with a profab 2.5" header, test pipe, and buddy club spec II exhaust. The weird thing is that I've never thrrown a code prior to replace the whole exhaust setup. Since I am running OBD1, I did not utilize the second O2 sensor which goes in to the cat. I have my primary O2 sensor plugged in to the test pipe because I could not fit it in to the header. Due to the position of the O2 bung on the Profab header, the O2 sensor hits the sway bar and cannot plug in at all. I've tried out three different O2 sensors and have always had the samew results after resetting the ecu. I constistently am throwing this cel code #1. Another strange thing is that the cel comes on randomly, usually when the car is fully warnmed up and has been driven for awhile. Again, when I try and decode the cel, it flashes once and is very dim that you can barely see the code. My question is, Am I reading the correct code or is this another issue. I am now in high oubt that my O2 sensor or ECU is bad. I have re-checked my grounds and they all seem perfectly fine. Any help or input would be greatly appreciated.