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Is that a dead cat?

pooga

Well-known member
Joined
3 Aug 2014
Messages
125
My 2003 C4S @166k failed emission test - running rich!

There are no engine faults or OBD2 codes

Running rich at idle - post-sensor mirroring pre-sensor - is this a sign that CATs are not doing their job?

I have plotted the o2 sensors (pre/post cat) reading from both banks. MAF reading and have tried to compare the data.

Can anyone help?
 

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Just to add....

I am running IPD plenum + BMC Air filter / high-flow 200 CELL cats / DMS Remap

AOS went and was replaced week before the initial MOT, ran cat-clean though and re-mot a month later - no difference to the emissions.
 
Both banks and pre cat lambda sensor is being mirrored by the post cat sensors.

That indicates both cats are not working .

There is normally a reason for 2 cats to fail though and thats a misfire or a rich mixture ie maf fault.

The pre cat sensor switching looks pretty poor to me .. that may or may not be a fault as it might just be the scope thats slow ..

It should look more like the attatched image although not quite that precise !
 

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Thanks for the response deMort

I just checked the temperature pre and post cat on both banks ~230F (i.e. in and exit of the cat) - assume this also confirms the cat!

I have order pair of Topgear Cats and the sensors/MAF are original so also ordered 4 sensors and MAF.

Thanks for your help!
 
is this normal for a cat??
 

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