Pico Technical Support and Discussion Forum

phreniform · Active User Joined: 13 Jun 2005 Posts: 8

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?

Autonerdz · Posted: Fri Apr 21, 2006 2:39 pm Post subject: O2

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.

mwebb · Guest

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]

ricardo · Moderator Joined: 07 May 2003 Posts: 98

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

Ric

phreniform · Active User Joined: 13 Jun 2005 Posts: 8

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.

Autonerdz · Posted: Mon Apr 24, 2006 9:35 pm Post subject: O2

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.

phreniform · Active User Joined: 13 Jun 2005 Posts: 8

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?

Autonerdz · Posted: Tue Apr 25, 2006 7:51 pm Post subject: Re: Oxygen floating ground

phreniform · Active User Joined: 13 Jun 2005 Posts: 8

Thanks for the info and downloads.

RobOnestop · Posted: Mon Dec 04, 2006 11:00 pm Post subject:

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

Autonerdz · Posted: Tue Dec 05, 2006 4:43 am Post subject: what is it

Looks like a negatively controlled saturated injector driver with the scaling wrong. Looks like a 20:1 attenuator is attached but PicoScope has not been told that it's there so the 14v circuit shows at .7v.

You will find the 20:1 selection under Settings/Probes. The way it is scaled from 0 to 1v (0 to 20) the injector kick is off the top of the screen. This is normally up to 80 volts. Select the 20:1 and then choose the +- 5v range to scale the screen to +-100 volts (with attenuator in place). Then you will see it all scaled correctly.

RobOnestop · Posted: Tue Dec 05, 2006 8:06 pm Post subject:

believe it or not its what i got from a lambda sensor

Autonerdz · Posted: Tue Dec 05, 2006 11:26 pm Post subject: strange

OK, you had me fooled. That's a classic injector pattern. You even have increasing voltage drop as the current rises. A bit noisy is all.

You need to increase the voltage scale and put some more time on the screen to get a few cycles in view and see the whole pattern. Could be some kind of pulsed O2 heater control. I don't have any info here on your application.

RobOnestop · Posted: Tue Dec 05, 2006 11:31 pm Post subject:

ive not had pico long so still finding my feet
whats the best setting for zirconia lambdas time base

Autonerdz · Posted: Tue Dec 05, 2006 11:44 pm Post subject: setup

You need lots of time on the screen to see the O2 cycles. Here is an example series at 1s/div:

http://www.autonerdz.com/cgi/yabb2/YaBB.pl?num=1114921447

These are standard Zirconia sensors pre and post CAT.

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