Are 02 sensors at cat. conv.

Rebuilding 97 Taco exhaust, and previous owner removed cat and now has sensors before and after muffler. I'm pretty sure the sensors should be before and after the cat, so do I buy a 12" or 18" cat. Thanks

 

If you have to weld in the cat then it might not make any difference, but my cat is bolt on and is about 18" total. 12" seems a little short to me for rear cat.
Did he make an extension for the sensor?

 

They should be before and after the cat. If you have them both before the cat, you will get a CEL.
The point of having a post-cat sensor is to check the operation of the cat. If the cat is burning waste fuel, the signal will be different than the pre-cat sensor. If they are both before the cat, the signal will be identical. It will look, to the ECU, like the cat is not working=CEL.

 

Yes he cut out the cat and welded a muffler between the sensors. Looks like I need to order a cat and move the sensors back to the cat. Thanks