Multiecuscan - pre-cat Oxygen sensor output voltages - Alfa 2L JTS engines - Alfa Romeo Forum
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(Post Link) post #1 of 7 Old 29-03-14 Thread Starter
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Multiecuscan - pre-cat Oxygen sensor output voltages - Alfa 2L JTS engines

I have a borderline high CO (Carbon monoxide) level which can be caused by numerous factors such as simply an old air filter, or worst case... fuel injectors. Before I touch anything, I would like to compare Oxygen sensor output voltages with another 2.0 litre JTS owner to establish whether my sensors are getting tired! Any contribution at some time will be appreciated.

To avoid confusion, I'm directing this message to members using Multiecuscan as opposed to other diagnostic software.
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Not sure about the JTS..
But I understand that most lambda sensor voltages should swing between 0.1V and about 0.9V with a frequency of about one second.
If the voltage is stuck LOW.. or swinging low.. eg. between 0.1v and 0.5V (lean) it will lie to the ECU which will force the engine to run rich.
can be measured using software or just a good old fashioned multimeter.
I would fit a new air filter first.. and then check the voltages..

EDIT.. read Sensingsys post below

Last edited by seadart; 31-03-14 at 13:50.
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Thanks for your reply seadart.

What a coincidence, I've just got in after replacing the air filter! in case it hadn't been done by previous owner.

Strangely though when I was playing with multiecuscan a few months ago I recall readings of around 1.5volts from both precat sensors which I thought were too high. Then recently I had a high CO level which may equate with a rich mixture. However, in view of this I would expect the lambda voltage readings to be below 0.5v.

I'll check readings again when I get my OBD lead back. If they are high, then it's multimeter time.
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I do have quite a bit of info about this, but only at tick-over, the info however is on my desktop PC and now I am on my laptop, I'll post tomorrow morning. Not as seadart said though, the JTS has completely different pre-cat lambda sensors than the TS.
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The JTS has wideband lambda pre-cat sensors, some info is here

A couple of graphs from my JTS is here, remember this is for tick-over only. 1.5V at tick-over is incorrect.

I had problems with Multiecuscan 1.8 showing false drops to zero voltage on the graphs due to 'latency too high' errors and so reverted to the earlier FiatECUScan 3.3 which worked OK.
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Thanks sensingsys.

I will take new readings probably over the weekend, compare with yours and post back. Now going to read up on wideband pre-cat sensors.
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very interesting thread! any news on that?
how do you know, that 1.5 V is incorrect for tick-over.? I read the Lambda readings of my JTS and they are also both just around 1.5 at idle. (under de-acceleration the voltage raises over 4 volt, which seems ok I think?)
2 graphs are attached. curious on doing more, as I have a random lack of torque in around 3k rpm without any error recognized.
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