1997 blazer qustion on oxygen sensor.
 

one of the 4 oxygen sensor are bad, or more. using my code reader it doesn't tell me which one so i might have to ohm them all out to see. I was thinking of buying 2 new ones. one before the cat and one after the cat. is it possible to tie the 2 other oxygen sensor from each bank into the oxygen sensor before the cat. basically having one oxygen sensor sending information to all 3 wires back to the PCM? Also what is the typical mpg for blazers iv been getting an average of 18 hwy and around 15 city. Thanks

What is the code?

Mileage sound right to me. I get 16.5 to 19 MPG on the avg combined. Sometime in the summer months I have gotten as high as 22 MPG on the road.

The other codes went away after i replaced the exhuast from the cat back i have a deffrent code now The code is P0340 i had a friend read it camshaft sensor. How does one go about fixing this?

A search for "CMP+sensor" or "camshaft+position+sensor" should turn up the pertinent details.