Replacing the oxygen sensor on the 1987 Mercury Cougar with a 5.0-liter engine requires you to work under the vehicle to access the sensors and wiring. The 5.0-liter engine uses four O2 sensors, two in the catalytic converter bodies and two in the exhaust pipe. The process for changing them is identical for each of the four, except that they are in different locations. To determine which sensor needs replacing, have a garage or parts store plug the code scanner in and retrieve the codes from the computer that will pinpoint the faulty sensor.
Tools Used: Jack, Jack stands, O2 sensor socket, Ratchet, Torque wrench
Change O2 Sensor
Raise the front of the car off the ground, using a jack and position a set of jack stands under the front suspension to support the car while you are working under it. Lower the jack, allowing the car to settle onto the stands and remove the jack from under the car.
Locate the O2 sensors from under the car. The catalytic converters are between the engine and the mufflers in the exhaust system, and the two sensors mounted in the exhaust pipe are in the down pipe just below the exhaust manifold.
Disconnect the wiring harness connector on the end of the pigtail from the sensor you are changing. Position an O2 sensor socket over the sensor and turn the sensor and socket counterclockwise with a ratchet until it is free. Remove the sensor from the pipe or converter and discard it.
Thread a new sensor in place by hand and slide the O2 sensor socket over it. Using a torque wrench, tighten the sensor to between 26 and 34 foot-pounds and remove the socket and torque wrench.
Connect the electrical connector from the new sensor to the connector on the car's wiring harness. Push the two connectors together until the locking tab snaps in place.
Move out from under the car and raise the front off the jack stands with a jack. Remove the stands from under the suspension and carefully lower the car to the car to the ground.
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