Well i've taken the plunge and got myself a new cat and the best part is it comes with a pre cat where the usual standard aftermarket crap doesnt ....... now im praying im going to finally get shot of my cat efficiency code when i get it fitted some time next week ...... other thing is do i need a gasket set for it as it says you musn't use exhaust paste upstream of the cat ....

If so mate,can you please take ALL details from it...i.e maker,part numbers etc......i emailed the one on ebay but he pushed for my registration number so i didn't bother,i beleive it was made by a company in Nottingham
Also can you tell me for definate if the front sensor bolts directly into the pre-cat? i have a explanation for the codes

I got mine for less than £130 all in including postage ..... getting it put on for £30 .... i just hope it cures my P0420 code 

Ok,i did a bit of online research and also spoke with a guy over here who makes stainless systems

The first sensor is effectively no use because...... on the factory set up the first sensor takes the measurement from the 'swirling' gases from within the pre cat box.
After it has been through the main cat and treated the measurement is then taken from the 2nd sensor.

As the aftermarket pipe has no pre-cat the gases travelled too fast 'past' the 1st sensor for it to take an acurate measurement.....

Both sensors measures in voltage so because the first sensor doesn't get an acurate reading the voltage fluxuates too wildly to be 'within tolerance' for the system of the car...

The set up should be...

1st sensor....voltage with rise and fall wildly
2nd sensor......voltage will be more constant

Because the 1st sensor is not getting a proper reading then the 2nd sensor will rise and fall wildly because it has nothing to compare it with (from the 1st sensor)

The EML will come on because the car's system registers that there is an emmision problem due to the fact that the first sensor is not getting a proper measurement reading,however it wont flash up a fault with the sensor because it is there and it itself is functioning properly

MonzaIain wrote on 29. May 2009 at 20:53:



The original set up has lambda before and just after the pre-cat so hopefully on this set up its going through both before the second sensor so should be nice and clean 

MonzaIain wrote on 29. May 2009 at 21:02:


The second sensor is behind the main cat on this one but i belive on the original spec fitted at production the second was just after the pre-cat .... but i may be wrong  ..... maybe one of the admins would know what the original set up would have been

I thought it was the pre cat that did the main cleaning up of the gasses and the main cat cleaned up anything that was left ..... one sensor before the pre and one after then gave the pre cat code when it lost its peak efficiency ......
Anyway on my new one the second lambda is after the main cat so it should be "cleaned " twice and hopefully stop the P0420 

There was a long thread on here a while ago about moving the second lambda to behind the main cat to help as well so thats why im sure the second was just after the pre cat on original set up 

MonzaIain wrote on 29. May 2009 at 21:14:


Should be sometime this week coming so i'll let you know