Emissions MOT fail

[Chrisgti6]

Not on a Clio, this is on my MR2 Roadster.

Sent it for an MOT yesterday but it failed on emissions. HC and Lambda were a pass but CO was over. Picture of the results below. It did previously have an engine that was burning a whole lot of oil, so there is potential for there to be some residual oil in the cat & exhaust system - would this cause high CO or am I best off looking elsewhere? I have a spare cat and exhaust I can swap over and some spare lambda sensors if needed, although I do have a decent diagnostic tool so might check out the lambda readings before swapping them out.

Obviously I only get one shot at a retest so is there anything I can look at in my diag tool to indicate if I've reduced the CO? Post cat lambda readings maybe?

 

[Mr Trailer Man]

High CO suggests a rich fuel mixture, but then the HC (unburnt fuel) is way low 🧐

See what your lambda readings are.

 

[Chrisgti6]

High CO suggests a rich fuel mixture, but then the HC (unburnt fuel) is way low 🧐

See what your lambda readings are.

Yes the lambda and HC results being where they are suggest a good fuel mixture, but high CO says otherwise which is slightly confusing!

What should I be looking for on the lambda readings? It has 2 precat and one post - would I need to be looking at all 3? Looking at voltage fluctuation I assume? I know my tool can record the results so i'll have to risk taking it out without MOT and get some readings done

 

[Mr Trailer Man]

Yes the lambda and HC results being where they are suggest a good fuel mixture, but high CO says otherwise which is slightly confusing!

What should I be looking for on the lambda readings? It has 2 precat and one post - would I need to be looking at all 3? Looking at voltage fluctuation I assume? I know my tool can record the results so i'll have to risk taking it out without MOT and get some readings done

Yeah the precat should be fluctuating steady wave up and down.

Post cat should be a steady line/voltage.