1 FMF

iTrader: (1)

Can someone explain or provide a link as to how the whole air/fuel ratio thing works, and how it is measured.

As far as I know, 14.7 is the AF ratio you shoot for. Higher than that is rich, less is lean?

All the OEM O2 sensors do is output a voltage, based on the Air/Fuel condition? What voltage range do they operate over?

I was looking at an A/F guage, by cyberdyne. It has a LED bar to indicate the AF condition, and says it can be used with existing O2 sensors. So does the guage just monitor voltage output of the O2 sensor, like a typical voltmeter would?

In my search for more info, I came across widebando2.com. And they explain wideband measuring vs. narrow band. Is the definition of wideband only a sensor capable of measuring air/fuel ratio further away from 14.7? Where in the exhaust is the measurement taken? On the LS1, there are 4 O2 sensors, correct? Two on each side, before and after each catalytic converter, so where/how do you perform an Air/Fuel measurement? That is what has me most confused.

Windy City

OEM narrowband O2's send a 0-1V signal that's proportionate to the A/F ratio.


That's exactly what they do. The gauge display is really just a reading of the 0-1V that the O2 puts out.


A wideband 02 can detect A/F ratios further beyond stioch and the output is 0-5V. Standard 02's become very inaccurate at A/F ratios for max power. That's why our PCM's go into open loop when at WOT. It can't accurately monitor the proper A/F ratio at WOT with the narrowband O2's.

The first set of 02's detect stioch and are used for conditions at or near stioch such as cruise, idle and part throttle. The rear set of O2's are used strictly to monitor the cats. In fact, if you remove the rear O2's, the car will still run OK and you'll only throw a SES light.

Hope this helps.

Camaroholic

iTrader: (1)

To expand a little...

A Narrowband is only linear with respect to air fuel ratio across a very narrow voltage range. Approximately 400-500 mV. The 'switching point' is 450 mV - this is supposed to be 14.7:1 AFR. Beyond these ranges, the response of a narrowband O2 sensor is nonlinear - and therefore unpredictable. 13:1 may be 900 mV. It may be 880 mV. It may be 920 mV. It's out of a "narrowband's" range. Think of a narrowband as a rich or lean indicator. Above or below 14.7:1. Nothing more.

The wideband O2 has a linear response (predictable) across a wide voltage range. For example, 10:1 to 20:1 may be represented from 1V to 5V. You can plot a graph of voltage vs AFR and it is a line (linear) and you can therefore make an accurate measurement of a wider band of AFR.