http://www.forparts.com/BoswidebandO2.htm

"The newest generation of oxygen sensors are being called "wideband" lambda
sensors or "air/fuel ratio sensors" because that's exactly what they do.
They provide a precise indication of the exact air/fuel ratio, and over a
much broader range of mixtures - all the way from 0.7 lambda
(11:1 air/fuel ratio) to straight air!

The Bosch LSU 4 wideband oxygen sensor is a 5-wire sensor that reads
oxygen in much the same way as a traditional oxygen sensor.  but it uses
the latest "planar" construction with a special two-part sensing element
to measure how much oxygen is in the exhaust."

End of quote.

Now all you need is the senor and a cheap digital voltmeter.
http://importblowoutsales.com/
http://www.action-electronics.com/panelmeters.htm

A wide band O2 sensor is essential for tuning any fuel
injection system.