hope i spelt that right hi im after some info on what these are, and what they do? and are they worth fitting? getting my exhaust done soon and ive heard about people welding these in, or a thread in so i can fit one at a laterdate,places were to buy would be usefull aswell
thanks in advance

 

lambda sensors come on all cars made after 1992/3 as standard - they are used to tell the ecu how much oxygen is in the exhaust gas so that the fueling can be adjusted accordingly - this is to keep the air fuel ratio at 14.7 - stoiciometric (i hink thats the spelling) which is the perfect combustion - commonly known as "Lambda 1"

thats in a nutshell

 

in addition to Gracelands post the reason people retro fit these is for closed loop running when off boost/part throttle. This helps with emissions and more importantly on a cossie off boost economy

forgot to add stu @ MSD offers this conversion and supplies the lambda sensors too

 

or to run a air/fuel ratio gauge obviously, narrow (pointless) or wideband (expensive)

 

and to add more - Stu's closed loop lambda conversion is THE way forward - 340 miles to a tank of fuel on the motorway with plenty of "adverturous" driving above 100mph

thats with T34 and greens, but even if you had greys, you'd see this similar economy too - maybe more around the 300 mark tho

 

Al there are two sizes of boss,
i have both, large for my wideband and narrow for my genuine cossie one which is connected to my p8 ecu
the small one is m12 x 1.25mm thread

not sure of the large one.
later 4x4 turbos have a small type boss in the exhaust housing of the turbo

 

Well ... the common size such as you buy from Factors is Spark plug thread.

The theory is .. At around Lambda1 (near the point of the theoretical stochiometric ratio - 14.7:1) the sensor (which ideally, should be as close to the burn as possible ... even in it ... that will come soon enough) becomes very sensitive to the oxygen content in the gases. The output signal follows the ratio of the burn almost instantaneously. The signal, by design may be a (+) one (for lean ratio) or (-) for rich. The ouput voltages vary by design .. Some (like the 4.6 Rover with GEMS) are 5v.
The sensor consists of a precious metal "foil" protected by a permeable porcelain cap .. Design varies slightly, but most are built with the same principles.
Also, design can denote the mumber of connections .. The first (in the Yank motors way back) was a single wire type. Earth is through the body .. This is improved by a separate earth (2-wire) then an internal heater element (3 and 4 wire) On the latest sensors, there are generally 2 earths, 1 heater, and a signal. The reason for heaters is to get the sensor heated up quickly helping emissions during warm-up. To add something else, many modern management systems allow the addition of extra oxygen during the warm-up, which gets the cat heated up quicker to working temp. To some extent, the 02 lambda signal is ignored or modified to help.
Most current Euro4 emission spec. cars will have a twin lambda system .. the front one basically works as described above, the rear (post-cat) monitors the output gases and picks up failures/problems. This will trigger an event in the management ECU.

That's most of it, I think!