Lambda Temperature Comp

[stevesingo]

Is there any requirement for Temperature compensation for Bosch Lambda sensors?

The issue is that the installed lambda (LSU 4.2) reads the same as a tailpipe lambda meterv(NTK type, unknown manufacturer) when the engine is idling, but as the engine is loaded and the returns to idle there is a discrepancy in Lambda value.

Any thoughts.

Steve

[Scott@FP]

Under certain conditions the tailpipe unit may be getting outside air sucked back upstream of the sampling tube and skew it lean.

[stevesingo]

If that is the case, then the tailpipe sensor would be lean all the time. In this case the LSU 4.2 in the sensor reads rich after load has been applied and the temps are high.

Steve

[RossB]

You do not need a compensation for temperature, the sensor heater control keeps the sensor cell within its opperating range of 700-800 degrees. You can check that it is doing this by looking at (logging)the duty cycle of the heater. If the sensor cell reaches 850 degrees the duty cycle will be zero. You can also log Lambda Zp which is normally around 80 but will go down to about 60 if the sensor is too hot. At 50 the sensor will fail. If the sensor has been coled down too much, which can happen with some fuels, Zp will go up. If it goes to 200 the lambda readings will not be acurate.
If the sensor is getting too hot you may have to re-locate it or mount it on to a thicker boss. If it is opperating within normal limits you may be seeing the effects of temperature change in the exhaust gas mixture.

[Martin]

Ross,

What is the ralationship between Zp and Lamda sensor temp? ( I know La sensor temp and EGT are not the same thing)
Is it constant?

[RossB]

Zp is normally maintained at 80 which is an indication that the sensor is at its optimum temperature (about 780 degrees). If you look at Zp in a log file it will normally be a straight line and can be used to confirm that the sensor is working correctly. The duty cycle of the heater is an indication of how much external heating is required to maintain the constant temperature of the sensor with a lower duty cycle providing less heat and indicating a higher exhaust temperature. The duty cycle will reach zero at about 850 degrees.