Re: O2 sensor readout (Air/Fuel ratio indicator)

[Scott=John=Mockry%Mktg%TM@banyan.bv.tek.com]

glen@mass.smc.COM (Glen Powell) Wrote: 
| I tapped into the O2 wiring where the sensor harness connects 
| to the computer harness, under the hood. (Some Text Deleted)
| knock-sensor wires. Easy. Though I paid like
| $65 for a _Camden Superchargers_ O2 display unit.....

Glen,

With this talk of an O2 sensor display unit, I was curious as to what 
the LED readout actually indicates. Does it have RICH / LEAN LED 
indicators or does it give the Air/Fuel ratio?

I have looked at the O2 sensor output with an oscilloscope and it 
normally oscillates between the upper voltage range (0.9 Volts- 
RICH-less oxygen) and the lower output range (0.1 volt-LEAN- more 
oxygen) at idle or steady cruising speeds. This oscillation occurs 
around 1 to 2 times per second at idle and slightly higher frequency at 
cruising speed. The oscillation is due to the fuel system being in 
closed loop operation and constantly changing the fuel mixture in order 
to keep it as close as possible to the 14.7 to 1 Air/Fuel ratio 
required for low exhaust emissions. It is my understanding that the O2 
voltage output at the high and low extremes only amounts to around a  
1% change in the Air/Fuel ratio. 

I have done some testing with a portable 4 - gas (O2, HC, CO, CO2) 
exhaust analyzer with Air/Fuel ratio readout and have found under 
sustained full throttle acceleration the air fuel ratio is closer to 
13.0 to 1 for more power instead of the ideal 14.7 to 1 ratio for 
lowest emissions. I know that the O2 sensor output is a flat DC voltage 
topped out at the upper limit (around 0.9 volts) under sustained full 
throttle on my 86 5000CS Turbo. Under deceleration the fuel ratio goes 
up to around 20 to 1 and the O2 voltage goes flat (bottoms out) at the 
lower limit (around 0.1V).  If you are trying to get accurate air/fuel 
ratio information I don't think the O2 sensor is capable of giving you 
the actual degree of richness or leaness you have.
Scott