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Oxygen Sensor Signal Check

  1. Remove ECM from instrument panel without disconnecting coupler. (Connect coupler if disconnected.) Warm engine to normal operating temperature and keep at idle.
  2. Connect voltmeter between terminal Nos. 10 (oxygen sensor signal) and 9 (ground). If voltmeter indicator deflects between zero and .8 volts when engine speed varies from idle to 1500-2000 RPM, feedback system is operating properly.
  3. If voltmeter indicator remains at zero, check for oxygen sensor lead wire disconnected, intake system leak, air/fuel ratio too lean, second air constantly sent to exhaust, voltmeter inner resistance too small, or faulty oxygen sensor.
  4. If voltmeter does not deflect and indicates about .8 volts, check for engine not warmed up (choke operating), defective coolant temperature sensor, defective WOT microswitch, or disconnected mixture control solenoid lead wire.
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