Mitsubishi Eclipse 1990-1998 Repair Guide

Non-Heated Oxygen Sensor

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OPERATION



See Figures 1 and 2

The oxygen sensor is usually located on the gathering area of the exhaust manifolds. All exhaust gas leaving the engine flows past the oxygen sensor. The oxygen sensor produces an electrical voltage when exposed to oxygen present in the exhaust gases. Where there is a large amount of oxygen present (lean mixture), the sensor produces a low voltage. When there is a lesser amount of oxygen present (rich mixture), the sensor produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich/lean switch. The voltage from the sensor is transmitted to the Engine Control Unit (ECU), which changes the fuel injection ratio accordingly. On later models, the oxygen sensor may be electrically heated internally. This allows for faster switching during cold engine operation.



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Fig. Fig. 1: Oxygen sensor location-1.8L engines



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Fig. Fig. 2: Early 2.0L engines were equipped with a non-heated oxygen sensor. Later models utilized a heated one

TESTING



If the oxygen sensor has failed, the driveability of the vehicle may not be influenced. Since the air fuel mixture ratio shifts toward the rich side, the driveability of the vehicle may become better. However, levels of hazardous components such as HC, CO, and NOx emitted out the tailpipe will be elevated. This is because the ECU is not controlling the air fuel mixture.

1.8L Engine

See Figure 3

  1. Before testing, make certain the engine is fully warm. Coolant temperature must be around 176-194°F (80-90°C).
  2.  
  3. Detach the oxygen sensor electrical connector.
  4.  
  5. Connect the positive probe of a digital ohmmeter to terminal 1 of the sensor connector. Attach the other meter probe to chassis ground.
  6.  



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Fig. Fig. 3: Use a DVOM to test the oxygen sensor-1.8L engine

  1. Repeatedly race the engine; measure the voltage output of the sensor. As the mixture becomes richer from repeated racing of the engine, the sensor output voltage should register 0.6-1.0 volts.
  2.  
  3. If the voltage output is incorrect, the sensor will require replacement.
  4.  
  5. Shut the ignition OFF, disconnect the test equipment and reconnect the sensor to the wiring harness.
  6.  

2.0L Engine

See Figures 4 and 5

  1. Detach the oxygen sensor electrical connector.
  2.  
  3. Measure the resistance between terminal Nos. 3 and 4. Correct resistance is approximately 12 ohms at 68°F.
  4.  
  5. If there is no continuity or if the resistance is not approximately correct, the sensor must be replaced.
  6.  
  7. Operate the engine until fully warmed up. Coolant temperature must be at least 176°F.
  8.  
  9. Using jumper wires, carefully connect terminal 3 to battery positive voltage and connect terminal No. 4 to a known good ground.
  10.  



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Fig. Fig. 4: Testing continuity of oxygen sensor-early model 2.0L engine



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Fig. Fig. 5: Measuring the oxygen sensor output voltage-early model 2.0L engine

Use extreme care when connecting the jumpers. Incorrect circuiting will destroy the sensor.

  1. Connect the probes of a digital voltmeter across to terminal No. 1 and terminal No. 2.
  2.  
  3. Repeatedly race the engine; measure the voltage output of the sensor. As the mixture becomes richer from repeated racing of the engine, the sensor output voltage should become 0.6-1.0 volt.
  4.  
  5. If the voltage output is incorrect, the sensor must be replaced.
  6.  
  7. Shut the ignition OFF, disconnect the test equipment and reconnect the sensor to the wiring harness.
  8.  

REMOVAL & INSTALLATION




CAUTION
The temperature of the exhaust system is extremely high after the engine has been run. To prevent personal injury, allow the exhaust system to cool completely before removing sensor from the exhaust system.

  1. Detach the negative battery cable.
  2.  
  3. Raise and safely support the vehicle.
  4.  
  5. Detach the electrical connector from the oxygen sensor.
  6.  
  7. Using socket MD998770, or equivalent oxygen sensor socket, remove the oxygen sensor.
  8.  

To install:
  1. If installing old oxygen sensor, coat the threads with anti-seize compound. New sensors are already coated. Take care not to contaminate the oxygen sensor probe with the anti-seize compound.
  2.  
  3. Install the oxygen sensor into the exhaust manifold. Tighten the sensor, using the correct tool, to 33 ft. lbs. (45 Nm)
  4.  
  5. Attach the wiring to the sensor.
  6.  
  7. Carefully lower the vehicle.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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