O2 voltage measurement with Select Monitor
18 January 2002, 10:33 PM
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Today tested the 02 reading (MY99 European spec. Turbo Impreza) with the Select Monitor. I saw a voltage of about .05 Volts less as measured with a multitester. (or Lambda Link) These .05 Volts are quite a lot when used for mapping! (I use a wire for ground which is connected directly to the down pipe)
Did somebody outhere had the same experience?
Mark Verhoeven.
Did somebody outhere had the same experience?
Mark Verhoeven.
19 January 2002, 09:42 AM
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I have had similar issues. I thought my car was very lean when testing with a 3Hz digital multimeter. Made no difference how I spliced into the cable or where I go my earth, but originally I thought these were issues - seems not.
On a Lambda link type system I see about 0.05V HIGHER - mainly I think because the signal is not particularly steady and the multimeter does not see the peaks, whereas a fast flashing LED does. I go off the most brightly lit LED to read mine.
Don't know about the select monitor, but there is a delay. I would have thought it should be accurate as the signal is going through an ADC in the ECU and being put out through the serial port. Perhaps the sample rate is too low? If the ECU only uses the sensor at stoich then it does not need to be able to pick up little flickers at higher voltages? And it probably doesn't have to be very accurate either just to see stoich.
I would think to pick up the best of the signal like a Lambda link it would need to sample at over 10Hz.
Hope this helps.
Stephen Done has been doing a project to interface to the diagnostic port, and knows all the codes for the select monitor and their frequencies etc - might be worth asking him.
Mail me if you don't have his address, and I could also attach that estimate TD04L 9B compressor map if you want also.
[Edited by john banks - 1/19/2002 9:45:47 AM]
On a Lambda link type system I see about 0.05V HIGHER - mainly I think because the signal is not particularly steady and the multimeter does not see the peaks, whereas a fast flashing LED does. I go off the most brightly lit LED to read mine.
Don't know about the select monitor, but there is a delay. I would have thought it should be accurate as the signal is going through an ADC in the ECU and being put out through the serial port. Perhaps the sample rate is too low? If the ECU only uses the sensor at stoich then it does not need to be able to pick up little flickers at higher voltages? And it probably doesn't have to be very accurate either just to see stoich.
I would think to pick up the best of the signal like a Lambda link it would need to sample at over 10Hz.
Hope this helps.
Stephen Done has been doing a project to interface to the diagnostic port, and knows all the codes for the select monitor and their frequencies etc - might be worth asking him.
Mail me if you don't have his address, and I could also attach that estimate TD04L 9B compressor map if you want also.
[Edited by john banks - 1/19/2002 9:45:47 AM]
19 January 2002, 09:45 AM
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John,
I get the same results with Lambda Link and Multimeter. Only the Select Monitor shows a lower voltage. I am a little confused now, as it is a "simple" DC voltage to measure.
Mark Verhoeven.
I get the same results with Lambda Link and Multimeter. Only the Select Monitor shows a lower voltage. I am a little confused now, as it is a "simple" DC voltage to measure.
Mark Verhoeven.
See my edit re Stephen Done.
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