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Club XM Forum > Petrol Specific Issues
I have an emmisions issue with my Turbo CT VSX

CO is 0.0
HC is 0 PPM
CO2 is 10.76
Lambda is 1.389

And therefore it will fail it's MOT, Should I just replace the lambda sensor? and what type is it? 1,2,3 or 4 wire?

And would this expalin why its doing 23 MPG?

Hi Stewart

So far as i understand the oxygen sensor is like a switch, it will switch between telling the ecu to run on a rich mix, for starting from cold and running under load to lambda (theoretical 'perfect mixture' of 14 to 1 by volume) for cruising and light load running. If the Lambda sensor has failed you will experience poor running of the engine difficulty starting from hot or cold and a fault code from the ecu.
Other things that can affect either the emissions or the performance of the oxygen sensor are, leaky exhaust system (especially between the oxygen sensor and manifold as this lets air into and gases out of the exhaust which gives the oxygen sensor false information, a vacuum leak would also cause problems so check the inlet manifold joints.
Is not sure how many wires your sensor will have or whether it is a heated type sensor or not, most of my experience of the Bosch engine management systems is working with the normally aspirated 8v engine but you should be able to trace the wire back from the sensor without too much difficulty.
Also who performed the gas test, was it carried out correctly with a correctly calibrated exhaust gas analyser?
The test was carried out by me!, with a crypton gas analzer (the sort that takes 20 mins to calibrate from startup) I've had one fail on a turbo 820 Vitesse rover befroe and just like this car teh engine was running fine however the Lambda was much closer to passing. I did ahve a holed exhaust on this car, which I have now fixed, howver the lambda reading is still up the wall.


Hi Stewart

I cant really help much more, But will try to explain your results, forgive me if you already know all this but if you know what the results are saying and it turns out not to be the oxygen sensor you will stand a better chance of finding the fault. The thing with your emissions results is they actually point to perfect combustion! (Gordon browns wet dream)
HC (hydrocarbons) are actually fuel or partialy burned fuel and petrol is almost pure hydrocarbons. CO Is also only produced when the combustion process is not perfect. CO2 is produced by all living things and is not very toxic. The problem is an engine does not burn perfectly because it is designed to give power, (which needs a rich mixture) economy and when power is not needed it will then switch to a lean mix or Lambda as its called for cruising when very little power is needed.
You can test the oxygen sensor and if you want i can dig out some instructions on how to do this, But unless there is anyone else here who can help further i would suggest a book like the Haynes engine management manual which should help you discover and correct any problems.

Best of luck
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