Warm DRIVEABILITY Test 9 - O2 Feedback System Check

1. Disconnect the 12-way connector from the computer. Connect a voltmeter to connector cavity "4" and ground. Voltage reading should be within one volt of battery voltage. If there is zero volts, repair wiring to connector cavity "4" for an open circuit to the battery.
   Fig 1: Computer 12-Way Connector

   
2. If voltage reading is okay, check the terminal in connector cavity "4" to ensure it is not spread apart causing a poor connection. Connect voltmeter to the O2 solenoid connector (Green wire) and ground. Disconnect and plug the vacuum hose from the computer.
   Fig 2: O2 Solenoid Connector & Ground

   
3. Connect a vacuum pump to the computer and apply 14 in. Hg vacuum. Start the engine and wait 4 minutes. Raise the engine speed to 2000 RPM. Voltage reading should be varying between 4-14 volts. If voltage reading is okay, remove the air cleaner lid. Close the choke plate. Voltage reading should drop toward zero.
4. If voltage drops, connect a tachometer to the engine. Connect a jumper lead to the O2 solenoid (Green wire) and ground. Engine speed should drop. If engine speed drops, proceed to WARM DRIVEABILITY TEST 10. If engine speed did not drop, replace the O2 solenoid.
5. If voltage reading in step 3) does not drop, disconnect the O2 sensor connector. Hold the O2 sensor harness terminal in one hand and touch the battery positive with the other hand. Voltage should drop. If voltage drops, replace the O2 sensor.
   Fig 3: Oxygen Sensor

   
6. If voltage does not drop, return engine to idle. Turn ignition off. Disconnect the 12-way connector from the computer. Connect a voltmeter to the connector cavity "11" and ground. Turn the ignition switch to the "RUN" position. Voltage reading should be within one volt of battery voltage.
   Fig 4: Computer 12-Way Connector

   
7. If voltage is okay, check the terminal in connector cavity "4" to ensure it is not spread apart causing a poor connection. If terminal is okay, replace the computer. If there is zero volts, repair wiring in connector cavity "11" for an open circuit to the carburetor 4-way connector.
8. If there is zero volts in step 3), turn the ignition off. Disconnect the 12-way connector from the computer. Turn the ignition switch to the "RUN" position. Voltage reading should be within one volt of battery voltage. If voltage reading is okay, replace the computer.
9. If there is 0-1 volts, turn the ignition off. Disconnect the O2 solenoid connector. Connect an ohmmeter between the O2 solenoid Tan and Green wires (between the solenoid terminals on 4-Bbl. models). The ohmmeter should should some resistance.
   NOTE: The amount of resistance is unimportant. Just ensure there is some resistance.
10. If there is an open circuit, replace the O2 solenoid. If there is resistance, connect a voltmeter to the O2 solenoid connector (Blue wire) and ground. Turn the ignition switch to the "RUN" position. Voltage reading should be within one volt of battery voltage.
11. If voltage reading is okay, repair the Green wire to the computer for a short to ground. If voltage reading is not okay, repair the Blue wire for an open circuit to the ignition switch.
12. If there is 1-3 volts in step 3), disconnect the PCV valve hose and plug it with your finger. Gradually allow air to enter PCV hose. Voltage reading should increase. If voltage increases, check for fuel contamination in the crankcase. Change oil and filter as necessary. If there is fuel contamination in the crankcase, repair the carburetor.
13. If voltage does not increase, disconnect the O2 sensor connector. Hold the O2 sensor harness terminal in one hand and touch the battery positive with the other hand. Voltage should increase. If voltage increases, replace the O2 sensor. If voltage does not increase, replace the computer.

Fig 5: Battery & O2 Sensor