AFR data logger

AFR Data Logger

I decided that i wanted to re-flash and re-map the ECU myself, so i needed a way of viewing the AFR during normal driving so purchased a Wego 111 AFR data logger

AFR data logger
AFR data logger

The WEGO III is a complete air/fuel ratio (AFR) metering system with built-in data logging. The system is a versatile tuning aid and diagnostic tool for all carbureted and fuel injected gasoline powered engines. The WEGO III unit displays AFR and can log over 2 hours data including AFR, engine RPM, and a spare 0-5V analog input for sensors such as throttle
position or manifold pressure. The ultra-bright daylight readable blue LED display features automatic dimming under low light conditions.

The system uses a low cost Bosch LSU 4.2 5-wire wide-band oxygen sensor. By utilizing miniature surface mount electronics technology, digital signal processing techniques, and a switching power supply
for the sensor heater, the WEGO III provides the same level of accuracy as lab systems costing thousands of dollars.

WEGO III units also have a 0-5 volt analog AFR output that is compatible with most data acquisition

AFR Display
AFR Display

The exhaust needs an 18*1.5mm bung welding in to install the wide band sensor.  I removed the existing narrow band sensor as i was re-mapping and I had already removed the Catalytic Converter.

I also needed to block off the PAIR valve as they introduce fresh air into the exhaust to burn off excess fuel, but this affects the readings of the oxygen sensor.

Conventional (narrow-band) exhaust gas oxygen sensors have been widely used in automotive applications since 1981.

​Conventional sensors have one to four wires and can only sense air/fuel ratio over a relatively narrow 14.5 to 15.0 range.

They are intended to be used with 3-way catalytic converters that require operation near the stoichiometric point (14.7 air/fuel ratio).

The range of narrow-band sensors is inadequate for performance tuning.  While originally developed for lab and specialized automotive, wide-band sensors are ideal for tuning. ​ The 5-wire Bosch® LSU 4.2 sensor used with the WEGO™operates over a range of 10.3 to infinite air/fuel ratio.

AFR data logger installation
Wego 111 Installation

The WEGO III display shows AFR and status data. The unit includes internal diagnostics for abnormal battery voltage (less than 11 volts or greater than 16.5 volts), sensor open circuit, sensor short
circuit conditions, and excessive temperature. When power is turned on, the display will show “CL” (cold) until the attached sensor has reached normal operating temperature. The unit will then display an AFR value,
“FA” (free air), “PC” (during PC communications), or diagnostic codes: “SO” (sensor open circuit), “SS” (sensor short circuit), “Lb” (low battery voltage), “Hb” (high battery voltage), or “OT” (over-temperature

The WEGO III will start logging data once the sensor has reached normal operating temperature and the unit displays an AFR value or “FA”. The unit will not log data when “CL” or “PC” is displayed.  The interval between samples can be set from 0.1-1.0 seconds using the WEGO Single
Channel Data Logging software. The unit stores the last 8,000 samples.


Higher AFR values correspond to a leaner (less fuel) condition. The practical operating range for most engines using gasoline fuel is from approximately 11.5 to 14.7 AFR. Combustion of a stoichiometric mixture
(exactly enough air to burn all the fuel) results in 14.7 AFR indication.

Automotive engines with catalytic converters operate near 14.7 AFR during cruise and idle. Race engines usually require a richer mixture to limit cylinder head temperature and prevent detonation.

The table below lists reasonable AFR values for engines without emission controls.