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Using A Wideband O2 Sensor In Your Car, Pt.1

This Wideband Controller is intended to be used with a Bosch Wideband LSU4.2 oxygen sensor and our Wideband Sensor Display to accurately measure air/fuel ratios over a wide range from rich to lean. It can be used for precise engine tuning and can be a permanent installation in the car or a temporary connection to the tailpipe of the exhaust.

By John Clarke

Main Features

• Accurate lambda measurements
• Pre-calibrated sensor
• S-curve output
• S-curve response rate adjustment
• Heat indicator LED
• Data indicator LED
• Engine started detection option
• Correct sensor heat-up rate implemented
• Heater over-current and under-current shutdown
• Optional fast heat-up if correct conditions are met

For precise engine tuning and mod­ification an accurate air/fuel ratio meter is a “must have”. An engine that runs rich will use excessive fuel and cause air pollution while an engine that runs too lean may be damaged.

Click for larger image
Fig.1: what's inside a narrowband zirconia oxygen sensor. It consists of a zirconia ceramic sensor element with thin platinum electrodes on both sides.

Unfortunately, trying to diagnose engine mixture problems with the standard narrowband oxygen sensor fitted to all cars is quite difficult. While it is good enough to indicate the stoichiometric mixture for use by the ECU, it is only accurate over a very narrow band; that it why it is called a narrowband sensor.

Typically, most engines should run with a stoichiometric mixture except when accelerating where the mixture may go richer. Alternatively, during cruise conditions and engine overrun, the mixtures might go lean. In contrast, some engines run at stoichiometric continuously, regardless of engine load.

So why do you need a controller for a wideband oxygen sensor? In brief, it’s because a wideband sensor is very different from a narrowband sensor. In its most basic form, a narrowband sensor has only one wire and this is the sensor output. There is another connection via the metal frame of the unit. Other narrowband sensors have an internal heater and these units may have three or four wires. Fig.1 shows a cross-section of a typical narrowband sensor.

By contrast, a wideband sensor has six wires. This is because it comprises a narrowband oxygen sensor, a heater and an oxygen ion pump which diffuses oxygen ions into or out of the chamber which is monitored by the narrowband sensor.

Fig.2 shows the basic set-up for a wideband oxygen sensor installation. At left is the wideband sensor with its six leads which are all connected to the wideband controller module. The controller module then has two outputs. First, there is an S-curve output which simulates the output of a narrowband sensor and can be used by the car’s ECU to control fuel delivery to the engine. Second, there is a linear 0-5V output which drives the Wideband Display Unit (as published in the November 2008 issue of SILICON CHIP).

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