dont understand this lambda pattern

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dont understand this lambda pattern

Postby jmolnar » Wed Sep 03, 2014 8:46 pm

hi

I took this pattern from a 1998 Bentley turbo r

it has a 4 wire zirconia sensor

The engine was warm when taken and engine was running perfect,no faults

I cant understand why the transitions from rich to lean are so slow and the waveform is so ecstatic

thanks
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jmolnar
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Re: dont understand this lambda pattern

Postby tode » Thu Sep 04, 2014 7:42 pm

Hello "jmolnar," I try to give an answer .... the oxygen sensor, which thou hast made the measurement is installed on a vehicle that meets an old anti-pollution legislation, which allows more emissions, a sensor so slow is not a big problem at least until the idle speed does not fluctuate according to the signal of the sensor (sensor too slow), it is certainly lambda with many miles of work, the important thing is the deltaV or l 'excursion between minimum and maximum, which must be at least 0.7V.
The signal is so "ecstatic", perhaps due to the connection of the black test probe, where you have it connected?
If you connect it to the battery or to the chassis can enter the noise, I saw that also added to the filter to clean the signal.
For a correct measurement should use the negative wire of the oxygen sensor is an electronic mass.
Sorry for my english .... :D
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Re: dont understand this lambda pattern

Postby jmolnar » Fri Sep 05, 2014 8:20 pm

Hi.
Thanks for your reply
.the signal does move by 0.7 volts.
Do you mean i should connect the black lead to sensor earth?

Thanks
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Re: dont understand this lambda pattern

Postby tode » Sat Sep 06, 2014 8:00 am

If the sensor has only one wire you can just connect to battery negative or chassis, but if the oxygen sensor has four wires,
two heating,
one signal,
one is an electronic mass, where the unit cleans the signal with the electronic filters, the signal that appears with the Pico is the one that also reads the engine ECU.
I think, that this signal is not linear, because the sensor is functioning good and is capable of measuring the small variations of oxygen in the exhaust gas, the oscillation is slow because it is the engine ECU that slowly adjusts the injection timing, if you expedite the oscillations should be much more rapid.
greetings
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Re: dont understand this lambda pattern

Postby ianboyle » Mon Sep 29, 2014 8:27 pm

Hey,

Just thought I'd throw an opinion in here if your still interested in the movements of the oxygen sensor. Now I'm still learning myself so please feel free to educate me I'm wrong.

But it looks like the sensor is reading correctly and the transitions are occurring quickly enough but shows an incorrect operation at the same time, due to there being a possible turbulent supply of rich and lean exhaust gases around the oxygen sensor. I have seen a similar pattern caused by an engine with slightly low compression on 2 cylinders, this caused the oxygen sensor to read erratically as fresh air made it into the exhaust through the exhaust valves on the compression stroke.

Why I think the oxygen sensor is good is that it is responding quickly enough but just not how you would expect it to. It can be seen to drop from 0.6V to 0.3V within 50mSecs that is by far the movements of an active and responsive sensor.

Also there is clearly very little noise in this image, you have correctly connected the scope probe it is just not what you would expect to see. Seeing the unexpected will become a common occurrence the more you explore vehicle electrics. Enjoy
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