I recently purchased a b18b swapped 1990 Crx. In it's current state it has no oxygen sensors or catalytic converter and guzzles fuel at an obscene rate. I am looking to install new sensors and a cat (along with a few other exhaust modifications). Do I need to do any tuning or calibration after I install these new sensors, or can I just "plug and play", if you will, and let the ecu do all the adjustments?

--- Any info you may have regarding where the plug location may be on the wiring harness would be very helpful as well (this is my first car and the previous owner sort of hacked together his own harness so I'm having trouble locating anything)

 

Hmmmm... let's talk tuning theory. IF your tune was really good... you should get fairly good fuel economy without a primary O2 sensor, especially on a day where conditions are similar to those when the car was tuned. Adding an O2 sensor should improve fuel economy, but fixing the tune will optimize it. A second O2 sensor and a cat will NOT improve fuel economy at all... just help you meet federal emissions requirements.