Lamder Sensor DE-CAT FAO BENR

[Steveold]

Hi all

I want to know how replacing the exhaust and or de-cating your car will effect the lamder sensor? On 1.2 16v the sensor is after the Cat so its going to cause problems??? It would end up knocking the whole mixture thing out and not run right. going back to a stored default and run with an engine light wouldnt it??

So how you fit one then???

 

[orlandopaulo]

not sure, but here in portugal, some told me to get the sensor out and put some isolation tape arround it.. dont know if it is necessary to do anything else..

somebody??

 

[BenR]

tape the sensor up......um, ok......

If its after the cat and there is only one, i wouldnt start fiddling with it. I can affect the way the ECU sees how the engine is fueling.

However, i have not decetted my 172 for this, and others have tried with no real problems......cheack and see

 

[BlackClio16v]

i got mine decatted and after a week the engine management light came on. I took it to a garage to get it tuned and his main suggestion was to put the cat back on cos u dont get that much of again from a 1.2 n e way. he is ordering a cd o that he can muck around with the settings on a chip ecu i think and to see if he can override the mode that it is in the now think it is called limpmode or summat that sounds like that i.e the engine knows summat is wrong but cannot place where the error is. He also advised me that cos the cat is off running it with the light on ie something wrong it causes the lambda sensor to sense abnormalities and make something switch in the engine that causes it to ware alledgedly... sorry for such a vage response check out http://www.edinburghcruise.co.ukwww.edinburghcruise.co.uk in the feature car section u can see ma motor if yer bored

 

[HILLY]

Yes, ive got a decat pipe and full one off system from ascar (sheffield) and after a week the emissions light came on. I have got Renault to take it off but a few days later its back on oh well!!!

As re to the sensor it idles a bit erratic but when running its great

Pics to follow soon as out of bodyshop

 

[Simon]

One way to stop the light coming on is to fit a resistor inline between the ECU and downstream lambda sensor - this then places the reading in the range that the ECU is happy with.

I had this done on my 172 - however they had to remove the downstream lambda sensor as they couldnt tap in near it and they tapped in closer to the ECU. This introduced new problems on cold start so in the end had it all put back and stuck the cats back on.

 

[Steveold]

So really in other words we are stuck with a CAT..... tut

 

[Simon]

One way would be to modify the ECU program to ignore the downstream lambda sensor. I reckon it is possible.

I did look at buying a kit that plugs into the Diagnostic port and then allows a PC, Windows Based PDA, Palm to be connected and you can then monitor loads of variables and even alter stuff.

On the phase 1 172 they introduced the two lambda sensors around december 2000 time and therefore the ECU must be slightly different between 1 with two and 1 with one lambda sensor. I was thinking of sticking the earlier ECU in but then found out it isnt as simple as that. The ECU has to be configured to take into account the immobiliser codes I was told.

Apparently the group N ECU will fit and isnt bothered about the downstream lambda - however im not sure how that effects the immobiliser.

So gut feeling is it is possible to run decat pipe but requires someone with electronic kit and knowledge of the ECU and program to make changes to ignore downstream lambda sensor.

 

[Nick Read]

My opinion is that if you dont want a cat and dont want any hassle, just buy an older car. If you buy a new car with a weird lamda sensor after the cat then its obviously there for some emissions control reason, and it will go wrong if you change the system upstream. On a valver the lamda is in front of the cat so it makes no difference to the ECU whether the cat is there or not

 

[Simon]

Majority of vehicles before end of 2000 will probably only have one lambda so early MK1 172s dont have the problem and will benefit from a decat pipe.

The downstream lambda sensor is used to check that the CAT is doing its job properly - e.g. working. The ECU checks the O2 reading before and after the cat and thus determines if the cat is working.

 

[Nick Read]

Yeah thats what I thought Si; in other words, take the cat out and it knackers it.

 

[BenR]

using a resistor will only lower the voltage reading it send to the ECU, so it thinks its running far cleaner than it is. So startup will be odd and part throttle runing could possibly be lean. Id not bother, gains are minimal....

 

[BUTRE]

hum... you can try a POT.

 

[BenR]

sorry, but i find a well rolled doobie is the best....