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Hi,

I am soon having a custom pipe put on the B6 ....precats out and race cats replacing mains. Can anyone please let me know where all the lamda sensors need to go with respect to the cat on each bank to prevent any problems with the engine management etc.

http://jhmotorsports.com/shop/catalog/e ... _56_61_240

Hi,

I've got exactly the same set-up.
The front lambda sensor goes in front of the "new" cat and the rear lambda sensor goes behind ( after) it.

Regards Chris.

I only relocated the main cat sensors. Oddly enough, I did not do this for about 1yr and in that time never had a CEL or problems getting through the MOT.

In order to get the most out of the exhaust tweak the ECU will need to be tinkered with.

BlingBling wrote:I only relocated the main cat sensors. Oddly enough, I did not do this for about 1yr and in that time never had a CEL or problems getting through the MOT.

In order to get the most out of the exhaust tweak the ECU will need to be tinkered with.

Can I ask then why you moved them if they weren't causing you any problems ?

TBH it was always my intention to relocate the sensors, because it is the norm, I just never got around to it. I thought it was purely luck going so long without a CEL. It may be due to the remap being performed with the sensors in the pre main cat position. I just do not know.

Oddly enough since relocating the sensors I have had regular CEL. Again I am at a loss to explain why. Not sure if it is related but they started to occur after my battery died a death and was not replaced for about 1 month. Before then no CEL. I did pass the last emissions test but it was not straightforward. There were many failures before eventually passing 2 of the 3 tests. I've checked the wires and they are not in the best of condition, chaffed, deterioration due to heat, so my intention is to install new sensors and see how things progress.

BlingBling wrote:TBH it was always my intention to relocate the sensors, because it is the norm, I just never got around to it. I thought it was purely luck going so long without a CEL. It may be due to the remap being performed with the sensors in the pre main cat position. I just do not know.

Oddly enough since relocating the sensors I have had regular CEL. Again I am at a loss to explain why. Not sure if it is related but they started to occur after my battery died a death and was not replaced for about 1 month. Before then no CEL. I did pass the last emissions test but it was not straightforward. There were many failures before eventually passing 2 of the 3 tests. I've checked the wires and they are not in the best of condition, chaffed, deterioration due to heat, so my intention is to install new sensors and see how things progress.

Did you have any issues on lambda cable length when you did move them?

The cables were slightly extended, possibly too much. This was due to me having custom downpipes and 200 cell main cat so the system grew a bit in length. When JHM talk about un-clipping and extending using the available slack it is based on a modified stock system. Getting to the cable ties is fairly straight forward although one is a right bi-yatch. IIRC Somewhere near to where the bell housing and gearbox intersect. If you search the net I am sure you will find an image showing how the cables are looped.

The rear lambda sensors are used by the ECU to set the fuel trims and are important.

I would check your fuel trims with VCDS ( Vagcom) - I think it's measuring block 32, off-hand.
If you are failing the MOT emission then something is wrong.
Like I said I have custom downpipes and exhaust with only one CAT ( 100 cell) in each exhaust side.
I've gone through 3 MOT's with no problem at all - the Hydrocarbon and CO2 emissions well within tolerance.

Also, use VCDS to check if your rear Lambda sensors are actually working - they do age and last approx 50,000 miles.
I had to replace my 2 rear lambda sensors at 45,000 as the CEl would come on and VCDS reported the problem.

Hoep that helps a bit.

Regards, Chris.

Forgot to mention - I'm on 65000 miles now and the 2 front lambda sensors are on there way out - VCDS is reporting that they are right on the tolerance limit.
It was hard enough replacing the rear ones, so I might get a garage to do the fronts.

nihc wrote:The rear lambda sensors are used by the ECU to set the fuel trims and are important.

I would check your fuel trims with VCDS ( vagcom) - I think it's measuring block 32, off-hand.
If you are failing the MOT emission then something is wrong.
Like I said I have custom downpipes and exhaust with only one CAT ( 100 cell) in each exhaust side.
I've gone through 3 MOT's with no problem at all - the Hydrocarbon and CO2 emissions well within tolerance.

Also, use VCDS to check if your rear Lambda sensors are actually working - they do age and last approx 50,000 miles.
I had to replace my 2 rear lambda sensors at 45,000 as the CEl would come on and VCDS reported the problem.

Hoep that helps a bit.

Regards, Chris.

Thanks for the info. What should I expect wrt to fuel trims? Also what are the limits for the sensors when you view the measuring block module?

I will be changing the sensors shortly which should improve things considerably. Both are logging either "slow to response" related errors.

BTW, here's a good article explaining the fuel trims:

http://wiki.ross-tech.com/wiki/index.php/Fuel_Trim_Info

The spec for fuel trims is +/- 10%

Regards, Chris.