I see this on a lot of post.... and i have a 1997 XJ6 L 4.0 american beauty... what is this and what are some of the symptoms of its failure?

tks jake

 

Those are your oxygen sensors.

Bad ones lead to poor gas mileage and failed emissions.

 

Knealy2 is bang on, as well as bad mpg and poor emmissions, they can also lead to idle problems, engine hesitation / stuttering and generally down on power.

They're usually not overly difficult to change and not too expensive.

They are a replacement item that is all too often ignored

 

The Lambda Sensor (exhaust gas oxygen - O2 sensor) is the key sensor in engine fuel control management. The ECM (Engine Control Module) uses the O2 sensor’s input to balance the fuel mixture, making it leaner when the sensor reads rich and richer when the sensor reads lean.

Lambda Sensors produce a voltage signal that recognises the amount of unburnt oxygen in the exhaust. The voltage varies according to the amount of oxygen in the exhaust compared to the ambient oxygen level in the air. The bigger the difference, the higher the sensor’s output voltage.

Sensor output ranges from 0.2 volts (lean) to 0.8 volts (rich). A perfectly balanced or "stoichiometric" fuel mixture is 14.7 parts of air to 1 part of fuel. This gives an average reading of around 0.45 volts.

The Lambda Sensor’s output voltage doesn't remain constant but cycles from rich to lean approximately once per second. In a new sensor, this transition takes around 100 milliseconds. As the sensor ages, the transition takes longer which is why sensors need replacing at around 100K miles.

Lambda Sensors only operate when hot (above 250 deg C). To reduce the warm-up time of the sensor, an internal heating element is used. These are Heated Oxygen Sensors (HO2S) which can reach an operating temperature of around 500 deg C in less than 10 seconds.

Shorter warm-up time means the system goes into closed loop faster which reduces emissions and improves fuel economy.

Graham

 

Graham:
Great write up except the part defining the voltage levels for the sensors. The article you posted is , I assume. referring to zirconium lambda sensors. The X-300 uses titania sensors which are resistive devices that operate in substantially the same way as zirconium ones, but at different signal levels.

 

Lambduh=small furry animal related to lambs but very stupid and rarely seen as they do things like walk across freeways, jumps off cliffs etc...
Youll often see a chuppakabra before youll spot a lambduh....

 

Ross,

Absolutely right.

I was trying to keep it as simple as possible to illustrate the basics of why the sensors are there, what they do and how they do it.

This thread could (and should) progress into a lot of detail.

Graham

 

Thank you for posting. This saves me a bunch of time.

 

Tks guys..... i will change them

 

And here I thought a lambda was a new born sheepda. I guess I should have listened a little closer when Genesisda sang about A Lambda Lies Down on Broadwayda.

 

Rather than just changing them, why don't you get yourself a cheap (~$20!) OBD2 dongle so that you can have a look at how well your lambdas are working?

I use a bluetooth one paired with my android phone and a couple of free apps, but there are various wired and wireless dongles that can be used with laptops etc. You can draw graphs of direct sensor output, look at the resulting fuel trims, log all the info you like onto a spreadsheet...

Everyone (I assume it can't just be me!) loves new tools & this must be the best value tool I've ever bought... well that or my favourite (biggest) hammer, anyway.

 

Is this why when you go get your car emissions tested they recommend that you get the car hot and leave it running while in line waiting your turn? I guess this applies to all cars not just Jaguar?

 

Where did you find one? My '95 XJ6 is it OBD1 or OBD2?

 

You can find these pretty cheap on the internet, search 'ELM327' the one I have.

The American market 95 is an OBDII

 

The HO2S get up to temperature very quickly but you also want the Cats hot before an emissions test and this takes a bit longer.

This is the main reason it's a good idea to have the vehicle tested with the engine up to temperature.

Graham

 

95 jags are OBD2. when running a inspection I have to lie and say its a 96 to get it to run a regular plug n play OBD2 test since OBD2 were not required till 96 and state machines here in Texas still list 05's as OBD1 which is a longer more PIA test. Jaguar came out with OBD2 a year before required in the US