Emissions MOT Query

[pvsmark]

Right my car has now failed three times on the emissions part of the MOT and its driving me nuts!

A few months back i fitted a decat and whilst doing this i damaged the manifold lambda sensor bringing the light on and poor mpg/running etc.

Now i replaced this and everything was fine, the light went out but then re-appeared a few weeks later but this was probably because of the decat as the car ran perfectly and mpg was normal.

I then swapped back to my Cat for MOT time and the light has stayed on since, the readings from the MOT are as follows:

CO 0.00% PASS
HC 5ppm PASS
Lambda 1.110 FAIL

I have checked for leaks and there are none so I'm unsure about what could be causing it, does the cat lambda affect this reading in anyway as that's the only thing left to try as the lambda i replaced has not been touched at all?

Also from time to time my temp gauge will fluctuate up and down would the temp sensor effect the emissions reading?

 

[Jay Payne]

yes temperature sensor would make the fueling incorrect.

Also are you sure you have no exhaust leaks?

 

[pvsmark]

Well no leaks apart from small hole in backbox somewhere but tester told me it wasn't enough to affect it but I will double check the size of it later and bung it up.

I shall test the sensor later or just get a replacement for it but would this only affect the lambda reading or would it screw all three?

The problem is their are so many things that affect this i'm just trying to eliminate the cheaper options first!

 

[Scrooge]

Give the tester £20 to hold the probe at a distanca Viola, a pass!

 

[pvsmark]

Give the tester £20 to hold the probe at a distanca Viola, a pass!

Yeah thats the next option, just want it sorted properly really as its doing my head in not being able to drive anywhere!

Can anyone tell me if the Lambda in the Cat will affect this reading or is it the pre-Cat sensor?

 

[Sean6545]

Give the tester £20 to hold the probe at a distanca Viola, a pass!

But all that would do is sense more oxygen?

 

[lemonnobby]

id be giving it a very good drive, did you fit a genuine one? maybe just faulty also check the plug where it plugs into

 

[pvsmark]

Think I have sorted it, there was a hole where the exhaust meets the backbox on the pipe so sealed that up and it should pass as the probe would have been right over the hole when tested. New exhaust time soon I think!

 

[st3ve]

Even the smallest hole in the exhaust effects the running of the car.

 

[Dunn]

As a future tip buy some emissions cleaner from Halfords for about a fiver
Works wonders and recommended by vosa for MOT
My Clios have always been a b*****d at passing emissions

And also the lambda in the cat does not control fueling for your future reference only the pre cat one does

 

[bunzee]

At the last MOT mine failed on emissions, replaced both lambdas as they were acting up, but I also had temp issues where the gauge tended to read either much higher or lower than it had originally so the temp sender was also replaced and then it passed no problem - and as a bonus the MPG also increased considerably.