MoTeC PLM - Manual (Page 10)

10 Meter Operation
At the end of its life the sensor becomes slow to respond and does not read
rich properly. The NTK and LSU are designed to be accurate for 50,000km of
operation in a road car, so the above figures are a conservative estimate.
Sensor lifetime will be reduced by contaminants such as lead, silicon, oil, etc.
Thermal cycling will also age the sensor more rapidly, along with exposure to
exhaust fumes without any heating control active (ie: not connected to the
PLM). Regular performance of the Free Air Calibration will maintain the
accuracy of the sensor over its lifetime.
Sensor Temperature
It is important to ensure that the sensor is not overheated due to incorrect
placement in the exhaust as this significantly reduces the sensor life. The
sensor impedance (Zp) is measured by the PLM, and this is a reasonable
indication of sensor temperature. Zp should be approximately 80 Ohms in
normal operation. If Zp is less than 60 the sensor is being overheated by the
exhaust and the sensor life will be reduced.
Lambda
Lambda gives a measure of Air Fuel Ratio that is independent of the type of fuel
being used.
Lambda 1.0 corresponds to the stoichiometric ratio i.e. when there is no excess
fuel and no excess air.
Lambda > 1.0 => Excess Air (Lean)
Lambda < 1.0 => Excess Fuel (Rich)
Lambda may be directly converted to Air Fuel Ratio for a specific fuel using a
multiplication factor. The PLM will display Air Fuel Ratio by loading the
appropriate configuration into one of the output tables. For more information,
see Setup | Display in the PLM Setup Software section.
A table to convert Lambda to Air Fuel Ratio for various fuels is given in Appendix
A – Lambda to Air Fuel Ratio Table.
Engine Tuning
The desired Air Fuel Ratio (or Lambda) is dependant on the tuning objective i.e.
Power, Economy or Emissions. Normally at full load the engine is tuned for