Emissions stopping me pass mot

MarKagei

Hello people,
I have taken my car for an mot I am reading 1.97 Co but it needs to be 0.3 I have changed my spark plugs and changes the cat. My air filter is in good condition will I need anything else to help pass the mot because it's still failing Oh and a computer said my lamber is working fine

Can and think of what I need to do

motorguy

I had virtually the same problem last week.

I've a Clio 2.0 172 and the HC emissions were off the end of the scale (2,000 something)

High Hydrocarbons are a sign of unburnt fuel.

Unburnt fuel tends to be a sign of a weak spark somewhere.

I changed the plugs on the Clio which were rather old and worn, then we checked the leads with a multimeter and they were fine.

Next step was the coil pack. It turned out that the old one had a hairline crack with evidence that water had got in, so we changed it.

Finally, I put a Cataclean cleaner into the tank when it was half full.

On the retest, emissions were down from 2,000+ to approx 595 with the pass rate being below 1,200. Still high, but its a modded car and next steps would be to look at cylinder compression, valve wear and injectors.

If you think your coils / coil pack are fine, then the only other thing i'd be doing would be a Cataclean treatment - Halfords £15.99

Silver-Surfer_2

How near is your test centre? Is it fully up to temperature when it's tested?

arcon5

How do you know your lambda sensor is fine?

MG,
Before compression etc you should be checking sensors.

motorguy

arcon5 wrote: »

MG,
Before compression etc you should be checking sensors.

Yeah, fair comment actually - though no error codes makes me think its something ominous.

Not hugely concerned on mine - its through MOT and I'm going to punt it on soon - i've found out the hard way i'm too old to tolerate coil over suspension!!

SailorSam

Before you go for a test, go for a fast run up the motorway and blast it.
It's better having a test with a warm engine.

motorguy

SailorSam wrote: »

Before you go for a test, go for a fast run up the motorway and blast it.
It's better having a test with a warm engine.

And for the sake of £15, stick a cleaner in the tank before you do it.

[Deleted User]

When I was always trying to get my old bangers through the test my garage used to tell me to change the oil and filters that usually worked. Oil change was the most important.

facade

High CO means it is running rich.

Pre-cat oxygen sensor is most likely culprit, especially as "The computer" says it is working fine- it should be reading that it is too rich.

arcon5

motorguy wrote: »

Yeah, fair comment actually - though no error codes makes me think its something ominous.

Not hugely concerned on mine - its through MOT and I'm going to punt it on soon - i've found out the hard way i'm too old to tolerate coil over suspension!!

Sensors won't always flag up an error code mate. Not until the feedback from them is outside the set range or until the misinformation is so bad the engine starts missing or something in which case the error is usually initiated by a different sensor such as knock sensor.

In my experience emissions failures is usually one of two things: a sensor or two; or rings and its dumping oil. Although I've seen many cars with the latter still scraping through.

As for coil overs, well, don't get me started on them!!

poppasmurf_bewdley

How is your oil?

Dirty oil will give a high reading.

Nice clean oil will help reduce the reading drastically.