The O2 Sensor


 

The O2 sensor should be a four wire unit on the 94 80s. Therefore it has a two wire heater element in it to quickly bring it on line and keep it there,  A signal return wire (Info to ECU) and a earth return to the ECU
for the absolute correct signal. The older 1 and 2 wire O2 sensors relied on exhaust gas to heat the O2 sensor/s to bring them to operating condition at approximately 350 deg Centigrade (slower to bring online). The 1 and 2 wire units are normally located close to or in the actual cast iron manifold and not in the engine pipe, the LC has its O2 sensor in the engine pipe well away from the manifold. The precious metal as used in O2 sensors are Titanium or Palladium.

The effect on engine performance is negligible in as much to say that the O2 sensor is a fuel trim device and is used/observed by the ECU in a closed loop mode for fuel economy and emissions. The closed loop mode (also called feedback correction mode) occurs above idle, ie: small throttle opening. This being normally in cruise mode when the ECU will look at the O2 sensor and the ECU will then adjust the millisecond duration (opening) of the injectors according to the signal received from the O2 sensor. Eg: rich signal 0.75~1.0 volt, Lean 0.10~0.4 volt. The O2 sensor must have a crossover voltage past approx 0.5 Volt each 1.25 seconds approx or less at high revs to correctly work within the parameters of the ECU. IE: a trouble/fault code will be logged.

The ECU fitted to our Cruisers have the ability to learn different parameters due to driving conditions, engine wear, sensor deviation within certain parameters and O2 information in general.

Some problems associated with O2 sensors. Not in any order of importance.
1. Bad mechanical connection to exhaust.
2. Blocked external air passage into sensor.
        (air does not enter to exhaust at all under any circumstance)
3. Bad electrical connections at the sensor.
4. Contaminated O2 sensor, IE: coated with leaded gasoline.
5. Carbon coated Sensor.
6. Physical damage.

As a another by-product of a flashing Eng check lamp the ECU could go into limp home mode (all parameters locked at base, ie: nil timing advance and fixed injection duration)

Regards
TJL
Syd
OZ