I've got the symptoms of a bad oxy sensor (hesitating, poor power, ect.) and I've decided to take the plunge and replace it. Bently says that the sensor is in the *** system prior to the cat. I can't find the thing. what do I look for and where should I look fo it (under the car, down from above the engine, ect.)? The car is an 80q. Mike Stump