Oxygen sensor ground connection

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Oxygen sensor ground connection

Postby phreniform » Fri Apr 21, 2006 11:52 am

What is the correct ground connection for an oxygen sensor test? Battery ground or sensor signal return. On my Renault Clio (4 wire sensor) the signal return has a small reading above 0v so I opted for the battery ground. The results are attached. I thought the frequency was rather sluggish and also there is noise on the wave crests. A gas test showed 0-.5 % Co at idle. Any ideas?
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Renault Oxygen Sensor.psd
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O2

Postby Autonerdz » Fri Apr 21, 2006 2:39 pm

Nice capture. In most cases, you would reference the scope to vehicle ground. Looks like that worked fine there. However some O2 applications use a floating ground with a significant difference to vehicle ground. In those cases you have to dedicate one channel to the test and place the scope ground on the sensor ground.

The switch time is a function of the vehicle programming unless you force a lean to rich switch with a snap accel or added fuel. This is how you would test the O2 for range and response. It should switch 90% of full range in <100ms. The snap throttle is good for this as it is initially lean on the gulp and then you get the sudden enrichment. Then simply measure the response time and range.

The hash is normal. If you want to filter it out you can use the current filtered mode.
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o2 sensor renault

Postby mwebb » Sun Apr 23, 2006 10:27 pm

Fiat 124 spider red 2k rpm w o2 spark X.psd [img]

that hash is not always normal , the ace misfire people use waveforms like this to identify misfire .

how do i upload psd files to this forum ?

[/img]
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Postby ricardo » Mon Apr 24, 2006 10:47 am

You cannot upload files logged in as 'Guest'. You will have to create an account to do so.

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Renault Oxygen Sensor

Postby phreniform » Mon Apr 24, 2006 8:47 pm

I connected my hand held scope ground to the oxygen sensor ground with only a slight increase in frequency.(Results not downloadable). Here is another psd file showing the same Renault Clio at fast idle (2000 rpm). I was somewhat surprised to see the frequency still above 1Hz and the DC at the same level.
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Renault Oxygen Sensor 2.psd
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O2

Postby Autonerdz » Mon Apr 24, 2006 9:35 pm

Changing the ground location will not affect the frequency. However, if your sensor has a floating ground, referencing the scope to vehicle ground will make it appear to float above the ground level, averaging a higher voltage that it really has.

It's normal for frequency to increase at RPM over idle.

Attached are an idle and a cruise RPM example from a 2001 Ford Windstar 3.8 V6. These are 3423 four channel captures so you will need to change converters in PicoScope to view them. There are four O2 sensors. Two upstream from the catalytic converter and two downstream. The downstream ones are mainly to monitor CAT efficiency. They have very little activity. The upstream ones are cycling.
Attachments
2005_04_20_058.PSD
Idle
(204.33 KiB) Downloaded 766 times
2005_04_20_061.PSD
Cruise RPM
(230.65 KiB) Downloaded 711 times
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Oxygen floating ground

Postby phreniform » Tue Apr 25, 2006 7:30 pm

It's interesting what you say about the floating ground of an oxygen sensor. I checked my hand held scope and there was no shift of DC with scope ground connected to battery ground or oxygen sensor ground. Pico states in their installation guide (Page 5) "Take care to avoid connecting ground input of the product to anything which may be at some voltage other than ground". This would mean connecting the scope ground to oxygen sensor ground and scope ground to battery ground. The effect of this would be to link the oxygen sensor ground directly with battery ground. Would there be any danger to the ECU in doing this?
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Re: Oxygen floating ground

Postby Autonerdz » Tue Apr 25, 2006 7:51 pm

I checked my hand held scope and there was no shift of DC with scope ground connected to battery ground or oxygen sensor ground.


That's because it is not a floater.

This would mean connecting the scope ground to oxygen sensor ground and scope ground to battery ground. The effect of this would be to link the oxygen sensor ground directly with battery ground. Would there be any danger to the ECU in doing this?


Because the scope grounds are common, one must use care not to feed current through the scope grounds. Therefore the warning. You can put a single channel signal and ground across a floating ground sensor, but then you cannot use any other channels or you will crossfeed through the grounds. Other sensors employ floating grounds too, for example, some VR magnetic sensors.

When using multiple channels, all should be referenced to vehicle ground.
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Oxygen sensor connection

Postby phreniform » Sun May 07, 2006 10:40 am

Thanks for the info and downloads.
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Postby RobOnestop » Mon Dec 04, 2006 11:00 pm

anybody exsplain this pattern on M reg 1.2 clio[/img]ive added waveform but cant see it here?
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clio_senlac_M696_SRR_90_dgrees.jpg
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