lambda sensor problem

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lambda sensor problem

Postby chrisehogan » Thu Apr 08, 2010 10:55 am

hi i am trying to test a cat and would like a little help on the following capture
http://www.theimageboard.com/uploads/94cyn0nm.jpg

in the lower (blue) trace there is a lot of vertical lines what does that mean is it interferance if so how do i clean it up ! thanks Chris
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Re: lambda sensor problem

Postby Matt Fanslow » Fri Apr 09, 2010 7:46 pm

My knee-jerk reaction was to say you had a connection issue. You may still but what is interesting to me is that it only happens as the signal moves up in amplitude.

You have to verify connection integrity first, which I think is a given. Is this a multi-wire sensor? I would be interested what the ground is doing. This could be just a failed sensor.

As a side note, I wouldn't test a cat using pre vs post cat lambda sensors.

Later, Matt.
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Re: lambda sensor problem

Postby chrisehogan » Mon Apr 12, 2010 12:09 pm

thank you for the reply a little more info i checked the connections and i also switched channels the close lines still remained on the post cat sensor i also did a gas check the c0 was high suggests the cat has gone never seen it before .
thanks

chris
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Re: lambda sensor problem

Postby Matt Fanslow » Mon Apr 12, 2010 2:43 pm

Did replacing the cat "fix" the hash on the post cat lambda sensor?

Thanks.
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Re: lambda sensor problem

Postby chrisehogan » Mon Apr 12, 2010 4:00 pm

cats £600.00 +vat customer is still thinking about it this is why i was so interested in the hash do not want to make a misdiagnos.
on the same subject why is it not a good idea to test the cat with pre and post sensors .
thanks

chris
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Re: lambda sensor problem

Postby Matt Fanslow » Mon Apr 12, 2010 4:23 pm

Are we so sure we know what the PCM is looking for to gauge conversion efficiency? Switch-rate is rarely used, even though service information may have you believe that. There have been examples of pre vs post cat sensor waveforms that would insinuate a bad cat yet the PCM passes them and bank to bank comparisons where they look the same (post cats switching) yet one bank passes and the other fails.

Later, Matt.
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Re: lambda sensor problem

Postby chrisehogan » Mon Apr 12, 2010 4:43 pm

so how does the pcm tell if the emmission is wrong after the cat it only has the post sensor and the fault codes available to the post sensor is limited ie heater fault or bad wiring or slow response.
thanks for the reply

chris
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Re: lambda sensor problem

Postby Matt Fanslow » Mon Apr 12, 2010 5:20 pm

chrisehogan wrote:so how does the pcm tell if the emmission is wrong after the cat it only has the post sensor and the fault codes available to the post sensor is limited ie heater fault or bad wiring or slow response.
thanks for the reply

chris


It uses the post cat lambda sensor but it doesn't necessarily compare switch ratio. Newer vehicles often use intrusive testing where the PCM, under certain conditions, forces fuel mixture rich and/or lean and monitors post cat lambda sensor reaction. The issue with using scan data or scope data on the sensors is we really have little idea what the PCM is looking for so how can we make a judgment call? If the PCM is making corrections to extend the life of a degrading cat, can we make that assertion based of the output of the post cat lambda sensor?
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Re: lambda sensor problem

Postby chrisehogan » Tue Apr 13, 2010 3:55 pm

thank you for the info more reading to be done on my part only trouble is the brain is nearly full :D

thank you again

Chris
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