[V8] O2 Sensor Readings

[cobram at juno.com]

I don't know if there is a discernable difference in the signal with or
sans the meter.  The O2 sensor output will tell you there is a problem
somewhere in the fuel system long before the car throws a code, or the
problem kills the O2 sensor.  Helpful on pre-OBD cars.  No BTDT on a V8Q,
but I know a few guys who've been able to narrow down fuelish problems on
XJS's that were driving them crazy...but then again, they were already
half way down that road since they own a Jag.  ;-)  

BCNU,
http://www.geocities.com/cobramsri/
We come into the world naked, screaming and covered in blood. Why should
the fun end there?

"urq" <urq at pacbell.net> writes:
> I don't see any mention of the input impedance of the unit ... so I'd 
> advise
> caution.  As was correctly pointed out earlier, the output impedance 
> of the
> OXS is very high, and connecting a low impedance meter will change 
> the
> reading.  
> 
> Over the years I've realized that there is very little value to be 
> gained
> from monitoring the voltage output of the OXS.  If you suspect it 
> is
> malfunctioning, make sure you've eliminated all other possible 
> culprits, and
> then simply swap the OXS out for a new one.  The ECU varies the 
> mixture all
> the time to validate stoichiometric, so any sort of messing with the 
> FPR or
> adding HC to the intake just becomes a variable the ECU deals with 
> as it
> drives the mixture to stoich as best it can.  
> 
> The best tool for figuring out what is wrong with the engine is to 
> use
> VAGCOM or equivalent.  Unfortunately it appears that ProDiag has 
> died ... so
> unless you already have one it is no longer an option.  With ProDiag 
> I can
> read out and clear the ECU codes, and I can take a test drive and 
> log the 10
> parameters the ECU provides.  I suspect VAGCOM has the same 
> capability.  You
> can tell right away if the ECU has decided that it cannot control 
> the
> mixture effectively (generates a code) or if it is responding to an
> erroneous input (like an incorrect coolant temp).  
> 
> Steve B
> San José, CA (USA)
> 
> -----Original Message-----
> 
> This is exactly the tool you need - short of an oscilloscope.
> There
> are also volt meters with similar functions (bar graphs) built in, 
> but
> they will set you back a good $300 for a nice Fluke or equivalent. 
> The
> cheapo meters are not worth much in this application.
> 
> Dave
> 
> 
> 
> > Here's one that you can mount inside the car.  
> It fits with 3 wires
> > (+12v, signal wire on O2 sensor, and
> Ground).
> > 
> > http://tinyurl.com/39bfnd
> > 
> > MikeL's V8Q was going through O2 sensors, the temp sensor was
> the
> > culprit.
> > 
> > He wrote to the u.washington
> list:
> > 
> > "It's easy to test.  let car sit
> overnight, then measure the resistance
> > between the 2 pins on the
> sensor.  Should be between 1.5 to 3 ohms.
> > 
> > Mine was at
> 4.5 and it made the car run so rich that you got a huge black
> >
> cloud when you stepped on it.  As well as a pile of soot under the
> > tailpipe
> > if you let it idle for 5 minutes.....
> >
> 
> > BTW,  This is what ruined my 02 sensor :-("
> > 
> > 
> > "d saad"
> <dsaad at icehouse.net> writes:
> >>
> >>
> >> I am not sure you can deduce much at all from this Scott.
> >>
> >> The
> >> O2 sensor is not easy to read.
> To do it right, you really need an
> >> oscilloscope.
> >> A nice digital volt meter with a calibrated bar graph
> >> would also work OK - as long as the response time was fast
> enough.
> >> The
> >> problem is that the sensor is a
> very high impedance device - so
> >> just
> >> hooking
> up your meter affects the output. And the output is not a
> >>
> steady
> >> state voltage - unless you are at extreme rich or
> lean condition. It
> >> is a
> >> non-linear device with
> the usable range being a very narrow band
> >> around a
> >> air/fuel mixture of 14.7. For most practical purposes, the
> sensor
> >> can only
> >> tell you if you are above or
> below this number.
> >> If you look at the
> >> signal
> with a o-scope, you see something like a square wave - with
> >>
> the
> >> duty cycle of the waveform indicating the mixture. A
> volt meter can
> >> give
> >> you a rough idea of the
> duty cycle - because it averages the
> >> readings, but
> >> it is a very rough indication.