See Figure 1
The oxygen sensor is a spark plug shaped device that is screwed into the exhaust pipe. It monitors the oxygen content of the exhaust gases and sends a voltage signal to the ECM. The ECM monitors this voltage and, depending on the value of the received signal, issues a command to the mixture control solenoid on the carburetor to adjust for rich or lean conditions.
The proper operation of the oxygen sensor depends upon four basic conditions:
- Good electrical connections. Since the sensor generates low currents, good clean electrical connections at the sensor are a must.
- Outside air supply. Air must circulate to the internal portion of the sensor. When servicing the sensor, do not restrict the air passages.
- Proper operating temperatures. The ECM will not recognize the sensor's signals until the sensor reaches approximately 600°F (316°C).
- Non-leaded fuel. The use of leaded gasoline will damage the sensor very quickly.
- Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
- Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (O 2 S) and battery ground.
- Verify that the O 2 S voltage fluctuates rapidly between 0.40-0.60 volts.
- If the O 2 S voltage is stabilized at the middle of the specified range (approximately 0.45-0.55 volts) or if the O 2 S voltage fluctuates very slowly between the specified range (O 2 S signal crosses 0.5 volts less than 5 times in ten seconds), the O 2 S may be faulty.
- If the O 2 S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a high float level. These types of mechanical problems will cause the O 2 S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the O 2 S test repeated.
- Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the O 2 S to detect a lean mixture condition. Reattach the vacuum hose.
- Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the O 2 S to detect a rich mixture condition.
- If the O 2 S voltage is above or below the specified range, the O 2 S and/or the O 2 S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.
REMOVAL & INSTALLATION
See Figure 2
The oxygen sensor may be difficult to remove when the temperature of the engine is below 120°F (49°C). Excessive force may damage the threads in the exhaust manifold or exhaust pipe.
- Unplug the electrical connector and any attaching hardware.
- Remove the sensor using an appropriate sized wrench or special socket.
- Coat the threads of the sensor with a GM anti-seize compound, part number 5613695, or its equivalent, before installation. New sensors are usually precoated with this compound.
The GM anti-seize compound is NOT a conventional anti-seize paste. The use of a regular paste may electrically insulate the sensor, rendering it useless. The threads MUST be coated with the proper electrically conductive anti-seize compound.
- Install the sensor and tighten to 30 ft. lbs. (40 Nm). Use care in making sure the silicone boot is in the correct position to avoid melting it during operation.
- Engage the electrical connector and attaching hardware if used.