Posted by Mark Robins on October 21, 2011, 12:33 pm
Year of Manufacture *: 1996 Engine Size and Code *: 1.8cc 7AFE
Hi Gents,
Got me this Toyota which is on it's way to the scrap yard if it costs to much to repair! It's only failed it's MOT on emissions and according to the emissions ticket I think it's just the cat... RPM 2840 CO 0.71 HC 191 CO2 14.25 Lambda 1.012
I decided to check the lambda sensor operation and got some curious readings/images. I remember something strange about Toyota lambda sensors can anybody out there enlighten me?
This is at a steady 2500 rpm.
There is no switching at idle speed even if you introduce an air leak!
Your Lambda reading points directly to a failed catalytic converter. I think you are referring to the wide-band lambda sensor commonly used by Toyota. How many wires has it got?
I have found through experience that if the CO is above MOT acceptable levels coupled with a Lambda reading above 1.00 then it points to a catalytic converter problem. If the Lambda reading was below 1.00 as I would expect with a high CO reading then something else could be to blame. However, if the CO is at silly levels say 3 - 4%, then the cat may be faulty but there will be another fault. This is based on believing the cat will only gobble up about 1 - 1 and half % CO. This was discussed a few years ago on I think this forum and noted it to be true.
However, saying all that, I always check all the other possible causes just to make sure, but more importantly to make sure there is nothing else wrong with the management system which will curtail the life of the cat.
With regard to the Lambda Sensor waveforms, switching looks ok for a zirconia type sensor although the trough could be a bit lower at approx 0.2v. The waveform at idle is however wrong. However, I am unsure whether it is of the wideband type to which Mark alludes. Hence my question.
Hope this makes sense. I do however have the feeling that someone is going to shoot me down in flames!
Hi Pete, Like you,I would also be checking out cat looking at those readings,a check on inlet and outlet temperature at cat is usually a good guide for failing cat.
Mark, Would be interesting to see readings at low idle when no activity at sensor. Regards Christy.
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on October 21, 2011, 7:15 pm, in reply to "