Re: [doc] Cat replacement / Lambda-sensor

[Martin Gutkowski <webmaster@xxxx>]

The lambda system reads the emissions* through the lambda sensor 
upstream of the cat, so getting rid of the cat will not affect the 
lambda system.

Getting rid of the lambda sensor will put the lambda computer into "limp 
home" mode and set the mixture a bit rich. You could dial this back 
down to anywhere between 1% and 2% and still pass a UK MOT and not 
damage the engine (1.5% is the setting for non-lambda european Volvo and 
Renault PRVs) but you'll still be relying on the lambda computer and 
frequency valve. The correct way to remove the lambda system is to fit a 
metering head that doesn't have a frequency valve port. However, once 
this is done, you've still got ignition timing appropriate for a leaner 
mixture. So unless you plan on changing Metering head, ignition 
distributor and control pressure regulator, there's not a lot of point 
in getting rid of the lambda sensor.

The cat bypass reduces load on the engine so it does make a noticable 
improvement.

Martin

* it actually reads the oxygen in the exhaust but this is used as an 
indicator of how complete the burn is in the engine and therefore what 
the emissions are

Stian Birkeland wrote:

> Hi,
>
> If you swap the cat with a crossover pipe, would this effect the Lambda-system?
>
> Would the Lambda sensor not be necessary any more?
>
> Would this also effect the actual CO2 emissions testing / passing on the MoT?
>
> Best wishes
> Stian Birkeland
> Norway
>
> VIN # 06759