Is there a difference with the o2 sensor that plugs into the header and the one that is before the exhaust??? they are both pre-cat mine is a 97 and its on the exhaust and i saw one thats on eBay that is one that plugs in the exhaust manifold.

Will this one work for me???

 

The only thing the 02 does after the cat is determine if the cat is doing it's job. If I'm correct that 02 only has 1 wire while the 02 before the cat is a 4wire

 

i dont belive you are correct on all obd2 cars both o2 sensors should be 4 wire the difference is the computer is programmed to see switching voltage at the precat one and steady voltage (around.5 volts) on the after cat sensor that shows its doing tis job if tis not switching