How should a Lambda printout look?

[First Alfa]

So on the way home from work in the GT 3.2, I had the OBD reader hooked up and I was monitoring the O2 sensors on bank 1 and 2. The readout is for 1/2 hour on the Warrego Hwy heading east into Toowoomba although I pulled up for a few seconds half way to reset the program. (I only have the free version)
I believe these are the 2 sensors in the exhaust manifolds upstream from the Cat?
I've had SS exhaust manifolds fitted to my GT so there's no pre-cats in the manifolds.
My Lambda sensors are coming up to 200000 kms and apparently they should've been replaced about 40000 km ago?
Trouble is I don't know what the ideal readout would look like.
I know they're supposed to oscillate but I would've thought put together they should look almost identical?
They are similar but there's also a few anomalies. Does this indicate one is dying?
Which one? Both?
I've read about putting fakers in but wouldn't this lead to a constantly rich mixture and much worse fuel economy?
Any advice appreciated.

[Ascari32]

As the engine is a V6, the plots will not overlay as alternate banks fire, giving a time delay between the two channels displayed - I would have thought? And your display kit is probably not that sophisticated, so there must be some doubt about accuracy.   

They don't oscillate as such, they track the fuel/air ratio of the "After - Burn", enabling the ECU to re - adjust the fuel injected to track the Stoichiometric figure embedded in the ECU as closely as possible. There will be differences/tolerances as it is impossible for the condition of the cylinders, rings, valves, spark plugs, inlet ports et - al to be identical and have aged/deteriorated by identical amounts. However, best get it looked at by people who are expert at these things - the engine at least deserves that.

If your economy has not nose - dived and power seems to be normal, I would ignore your plots. It may be entertaining to look at them, but not if it scares the hell out of you. Otherwise, get into research mode and buff up on everything regarding Lambdas, MAF's, Air flow ratios, sensors, etc, etc.

And to fit fakers implies you feel things have deteriorated. If so, it is better to solve the problem, rather than hide it.

One has to be very unlucky for components not to outlast what the manufacturers quote. Generally they last well beyond their apparent working lives. 

[bonno]

Not sure this helps but I found this  Youtube video that explains typical lambda (02) sensor readings and what readings identify a faulty sensor.  The difference in wave form values between left and right banks is not unexpected as differing rates of deterioration of the injectors over time. The typical values on your graph should read in the region from 0.1 – 0.9 Volt.   
https://www.youtube.com/watch?v=npShfd7raoc
cheers
bonno

[Ascari32]

Good call - good video, very informative.

[First Alfa]

After watching the video I'm a little/lot less concerned now.
Still the readouts are an interesting snapshot.

[Colin Edwards]

Hi First Alfa,

What's the vertical scale and horizontal time base values?

[First Alfa]

The vertical (Y) axis is in mV from 0.85-1.15
The horizontal (X) axis is Time.
Total time is 31 minutes although the OBD will give a reading every few milliseconds depending on how many parameters you're measuring. In this case only 2.

[bonno]

Hi First Alfa
From the figures quoted, I would suggest your car is running a rich mixture. I have included below links to some useful videos in helping to understand the workings of a Lambda/(O2) sensor, together with diagnosing a bad sensor.
How it works Lambda sensor (refer to screen @ 33 sec mark for rich and lean mixture)
https://www.youtube.com/watch?v=ybLuvPw5BME&t=13s
Testing using multimeter and replacement of Lambda O2 Sensor.
https://www.youtube.com/watch?v=_Kr-c8eBl5E
How to know if Oxygen sensor is bad demonstrated on BMW using OBD2 scanner 
https://www.youtube.com/watch?v=O-UNkev5HWM

[Colin Edwards]

Hi First Alfa,

All things being pretty much equal, the O2 sensor for each bank should "see" pretty much the same thing. 
Not 100% certain on the O2 sensors on your GT, however O2 sensors typically compare the oxygen in the exhaust with ambient oxygen.  The output of the sensor is proportional to the difference between the two O2 levels.  The ambient oxygen can reach the sensor internals via a breather on the body of the sensor or via the space between the copper conductors and the insulation.  Ambient air will enter this space via the connection between the sensor wiring and the car wiring loom.  If the breather hole in the sensor body is blocked or someone has sealed the connector in an attempt to keep out water thinking moisture is a problem, the O2 may function out of range.  The O2 in the ambient air is essentially the reference.

The voltage should "dither" around an ideal set point of about 0.45V.  Voltage may rise to say 0.9V then decay to say 0.1V.  IF the O2 output is doing this at a fairly constant frequency, fair chance the sensor is reasonably ok.  The frequency the trace dither is set by the bandwith of the EFI.  Its not unusual for this frequency to be say 5 < 10Hz.  It is important the O2 sensor reliably responds to the regular mixture changes set by the EFI.

I used to use O2 sensors to tune Kart race engines.  Fed by a carby, the O2 output looked nothing like you would see on a four stroke car engine, however the sensor can be tested for response to O2 levels.  Whip out the iffy sensor and connect it to a high input impedence meter or even better an Oscilliscope.  Stick the sensor probe in a gas flame.  Butane works well.  When the sensor heats up, moving in and about the flame should resulting in predicable output changes.  Part of the flame will have lots of O2 in it - some with little to no O2.  Moving the sensor about the flame will reveal where the O2 is and where the O2 is not.