Technical O2 sensor readings

[ivand]

Could someone please tell me if these Lambda graphs are OK...
The car is Stilo 1.6.

(warming up):

(warm engine):

It seems that average cycle time is arround 1.39 seconds (between two maximum peaks), and that the graph is „lowered“ as if it's getting a lean mixture.
I am having problem with LTFT&STFT values, as they are high at 25-35%, and the car consumes above that it should.
I have removed problems due to misstiming belt, also checked and verified MAP readings, cleaned throttle body, cleaned injectors, replaced spark plugs, passed MOT with good lambda results:
....................@idle................@2800rpm
CO(%).............0,006................0,021
CO2(%)............15,64...............15,64
HC (ppm)............7......................9
O2 (%)..............0,250...............0,180
Lambda.............1,010...............1,007

Lastly I did some measurements with ECUScan, and got this:
O2 sensor pre-cat average value is about 0,41 volts (warming up);
O2 sensor pre-cat average value is about 0,361-0,401 volts (warm engine);
while O2 sensor after cat stays between 0,83-0,88 volts.
O2 sensor with ignition ON, engine OFF gives 0,014Volts.
Also I have checked resistance of O2 sensor heater, and it is about 14 ohms which seems good.

Somewhere I have read that O2 sensors can prematurely loose it's ability to perform best, giving results as there is lean mixture. Is it possible that lambda was damaged when one of the coils failed, and I drove car (on three cylinders) for about 10-15 miles to service?
Is it possible to clean this sensors?
Anybody ?

 

[ivand]

Hmmm,
I took some time to read about O2 sensors and their failures.
One of the reasons why they prematurely fail (or lose sensitivity) is the presence of the oil vapors in air intake, which are leading to carbon deposit on O2 sensor itself.
So, for the first thing to do, I took car to service for draining excessive oil from engine. There was about 0.4 litres more oil then it should be. But this is after about 3000miles that I made with car, so probably there was even more oil from the start.
It seems that I have slightly better mpg now, but I should wait a bit before to be sure 100%.
Maybe the deposits would be cleaned-off from O2 sensor after some time, simply by riding the car... who knows?
Whatever happens, I'll be prepared to get new one installed.

 

[hanzs]

I think, that O2 reading are ok. From 0,1V up to 0,8V, middle is around 0,45V thats ok. You passed the MOT - that proved, that all in engine is ok.
What is your fuel consumption now? My is now 8 litre/100km - I do everyday trip to work 30km and 30km back, 1/3 of distance is citydrive.
My best consumption 6,5l - easy country-drive (cca 80km/h).
Highway drive (cca 140km/h) - around 9 litres.

Deposits on o2 sensor can be burned by hard power drive - this cause high temperature exhaust gases, that can burn the deposits.

You can better see o2 reaction time on graph taken with FES + KKL cable on max. possible frames/sec settings.

 

[ivand]

I think, that O2 reading are ok. From 0,1V up to 0,8V, middle is around 0,45V thats ok. You passed the MOT - that proved, that all in engine is ok.

No, the middle that I measured is at 3.6-3.8 Volts, which is "lean" mixture.

 

[hanzs]

When its really lean - you should have less fuel consumption... but thats not true.
And I repeat - you passed MOT - so your engine management is ok, If mixture is lean or rich, you cant pass MOT. There is a small window of ideal mixture for passing MOT.

 

[ivand]

Well, I'll try cleaning it first. I've already made socket for it.
If this woudn't work, I'll put new one.

If it doesn't work after that, guess the problem is in fuel pump pressure (but I don't beleive it's fuel pressure problem).

I don't remember if I mentioned it before, but I had excessive oil on dipstick for arround 1 year. Mechanic told me that it doesn't matter, but I dont beleive him anymore. Probably the problem started from there.

 

[ivand]

Hi again!
I managed to remove lambda sensor this morning with some kind of "tool" that I made.
Was very nervous about possible cracks and damages that can come with it, but it was
really easy to remove it.
Also I've put sensor in vinegar (9%) fo an hour. After that it drove normally, so I can assume that this acid is not doing any harm to sensor. Some of the particles came off the sensor but I'll leave it over the night. Then we shall see what will happen.
Also I prepared some extra money for new one if something goes wrong.

 

[ivand]

Just 4 an update...
After shorter cleaning I did not achieve any benefits...Maybe I'll try again and let it soak for longer period.
Anyway, also I did test with voltmeter directly from oxygen sensor (as recommended by Decks) and what I've got is range of volts from 0.090 - 0.733. In the same time, the aftercat voltage is 0.83 which is higher that it should be (compared to precat voltage).
In short, I think that precat sensor has lost it's life, it sends less voltage then it should, and the engine is constantly overfuelled (running or richer mixture).
To end my worrys I have bought new lambda sensor and allready mounted it (95USD).
Let's wait for a while to get it checked with OBD diagnostics.
From the first hand, car is performing better I can feel it. But the numbers of LTFT STFT would show am I too subjective.
I'll keep you posted anyway.

 

[ivand]

Well everybody, think I've solved the problem.
Conclusion: premature failure of oxygen sensor due to excessive oil in engine (that's what I beleive ).
After installing new precat oxygen sensor, and after a few shorter rides, I got new measurements of precat sensor.
The signal is now changing from 0.073V(min) to 0.825V(max) all @ idle after warming up engine. Previous values (before replacement) were from 0.090V(min) to 0.733V(max) (as told in previous post). That is, I beleive, significant improvement.
Also, the signal of aftercat has "dropped" from 0.83V to average 0.816V.
Here is snapshot of graph:


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LTFT is now at arround 13%. Before installing new sensor it was 40%.
Is this going to drop down after some time ??