Wideband Air/Fuel ratio meter guide

Warning !!!

This wideband air/fuel meter must be installed by a certified mechanic. 

Koso North America is not responsible for any damages that might be cause to the vehicle or its users during of following the installation.

  • Do not cut or modify the sensor or wiring harness
  • Do not connect or disconnect the sensor when the instrument is working
  • Do not apply voltage above 18 volts DC
  • Do not open or modify the instrument or sensor
  • This instrument should be used as a tuning tool or race instrument.
  • Connect the instrument only on 12 volts DC power
  • Due to the nature of its use, the BOSCH LSU4.2 sensor is not covered by any warranty.
  • Koso air/fuel ratio instrument is covered for any manufacturing defect for a period of 6 months following the date of purchase

Wideband Air/Fuel ratio meter facts

The first role of and oxygen sensor is to communicate to the ECU or the gauge if the engine is running lean or rich. The goal is to have the motor run at 14.7 parts of air for 1 part of fuel (Lambda 1). Having the engine running at 14.7 to 1 would represent the optimal exhaust combustion.

O2 sensor facts

The Koso wideband air/fuel ratio meter is currently using the BOSCH LSU4.2 sensor. The 5 wires wideband oxygen sensor is the most accurate sensor on market. This sensor is able to read from10.0 to 24.0 to 1. The operating temperature of the sensor should not exceed 1 700 degree F. Using the sensor with leaded fuel or on 2 strokes engine will shorten the life of the sensor. Using a sensor bung adaptor will help extend the life of the sensor.

Calibration of the instrument

Each BOSCH LSU 4.2 oxygen sensor is individually laser trimmed with is own value for better results. The LSU 4.2 sensor is using a unique ‘’breather’’ system located on the connector (figure 1) to calibrate himself. This mean the sensor is self calibrating with the ambient air so there is no need to calibrate the sensor. This process replace the ‘’free air’’ calibration procedure when changing the sensor or using the unit on another exhaust system was needed. It would be very important not to block the cap above the breather (figure 2) due to the fact that the sensor is self calibrating by ‘’breathing’’ air from this hole.

Fig2-AFR sensor location-02Figure 1
Fig1-AFR sensor location-02Figure 2 O2 Adapter-04
Figure 4

Oxygen sensor installation

According to the oxygen sensor manufacturer, for better results, the sensor should be installed at the warmest location on the exhaust system. This would usually represent the first part of the exhaust which would be 300 to 500 millimeters from the piston skirt (figure 3). On a 2 strokes engine, it is strongly recommended to use a sensor bung adaptor to lower the impact of oil contamination (figure 4) on the O2 sensor. The sensor should be assembly with high temperature non permanent grease and tighten at 40-60 Nm. The use of cleaning fluids at the sensor plug is not permitted. Avoid any water or condensation on the tip of the sensor otherwise it might damage the internal components. Sensor must be installed with an angle of at least 10 degree (figure 5). Thus preventing the collection of liquids between sensor housing and sensor element during the cold start phase.

Fig3-AFR sensor location-02Figure 3 Fig5-AFR sensor location-02
Figure 5