To fully understand why a high performance vehicle tuner would be better off using a wide-band O2 sensor/gauge versus a narrow band setup, we must first understand what each sensor was originally developed to do.
Narrow Band O2 Sensors began to appear on vehicles with the advent of fuel injection in the 1980’s. Their purpose was to monitor component degradation (i.e. fuel injectors, vacuum leaks) of vehicles as they accumulated miles. Their basic job was to let the computer know whether the vehicle was running at an air/fuel ratio of 14.7:1 under idle (ideal ratio for gasoline engines), moderate acceleration, and cruise conditions, and if it wasn’t, to “trim” the injector pulse-width to either slightly lean or richen the engine. When the computer is paying attention to the input from the O2 sensor, the engine is operating in a “closed-loop” capacity. Under heavier acceleration or wide-open throttle the computer ignores the O2 sensor because it requires an air/fuel ratio other than 14.7:1, which is outside the design parameters of the sensor. This is known as “open-loop” operation. The sensor lets the computer know if the engine is running above or below 14.7:1 by sending voltage to the computer in a range between 0 and 1 volt, usually sweeping between the two extremes of this scale. Traditional narrow-band air/fuel ratio gauges are simply a voltmeter for this signal. This can be seen by the repeated sweeping back and forth of the gauge in most idle, light throttle, and cruise conditions. To summarize, a narrow band O2 sensor is only able to tell a computer (or gauge, for that matter) whether an engine is operating above or below a 14.7:1 air/fuel ratio.
Wide Band O2 Sensors where developed in the early ‘90s as vehicle manufacturers began looking to obtain air/fuel ratio information under all circumstances. This ranged from WOT to varying ratios, for example running air/fuel ratios leaner than 14.7:1 under cruise conditions. Volkswagen and Honda pioneered the development of the wide-band O2 sensors to provide accurate air-fuel ratios under these varying circumstances. They did this by broadening the voltage range in which feedback from the sensor was provided and making a linear scale that provided a fixed voltage that correlated to a specific air/fuel ratio. While the narrow-band O2 is still the most common type of O2 sensor installed on most new vehicles (for cost reasons), OEMs will still use wide-bands on many forced induction applications (or, in Honda’s case, on their “lean-burn” Civics).
High performance vehicle tuners discovered that wide-band O2 sensors are very helpful when accurate air/fuel ratio readings are required to maximize power, reliability, and mileage on modified vehicles.
This is my wideband gauge:
