MoT fail on CO reading

[100SRV]

Hello, my 1996 1 litre Ax has an MoT fail on emissions, data as follows:
rpm 2355
CO 0.585
HC 116
Lambda 1.027
Mileage 126215

I regularly get 55 to 60mpg and it doesn't burn oil excessivly...

The following have been suggested as possible causes:
coolant temperature sensor out of limits
Lambda sensor fail
catalyst fail

I have not long changed engine oil and filter but not the air filter (this I will do now).

Have missed anything?

[paintman]

Not had a cheap replacement cat has it? They might get you through an MoT when new but not likely to do it the following year - guess how I know that one!
Had this twice with two 1.6 306's. One with a 12 month old pattern cat just couldn't get the CO low enough & the HC was about the same as yours. Fitted a used genuine one which we happened to have from a scrapped 306 & the emissions went to virtually zero!
The second one JUST scraped through this year. It came fitted with a pattern cat identical to the first car. These pattern cats are half the size of the real thing.

According to the BET test, your HC is fine - less than 200ppm, your lambda is within the limits (should be between 0.97 and 1.03, which it is).
More in the flowcharts you will find on this link: http://www.motuk.co.uk/manual_730.htm

Edited by paintman on Monday 20th September 21:13

[fatjon]

That's so close to a pass that I reckon an air filter and a set of plugs may well see it scrape through for another year.

[davepoth]

Clogged air filter and dodgy plugs would easily do that. CO is usually down to an excessively rich mixture, which you'll get if the air filter isn't letting enough air through.

[100SRV]

Hi all,
thank you for responses, the air filter is used but not excessively dirty - you can see that the paper is yellow but the base of the pleats are dark. The spark pugs are a dark biscuit colour.

Motor factor shopping list now has:
front position light bulb
air filter
spark plugs
number plate (spacing incorrect)

[jagracer]

Take the air filter out and try again.

[russell_ram]

I think I'd be replacing £10 or so's worth of engine ECU temp sensor first if it were mine. High HC, lambda in spec, very high CO - running on cold start settings even when fully hot?

Edited by russell_ram on Tuesday 21st September 23:27

[100SRV]

russell_ram said:

I think I'd be replacing £10 or so's worth of engine ECU temp sensor first if it were mine. High HC, lambda in spec, very high CO - running on cold start settings even when fully hot?

Edited by russell_ram on Tuesday 21st September 23:27

Thank you russell_ram, less than £20 saw me fit a new temp sensor and air filter.

there are two sensors on the 1 litre engine, one in the block the other in the thermostat housing before the thermostat. Guess what the haynes manual doesn't tell you?

I changed the sensor in the 'stat housing as this had two terminals whilst the sensor in the block only had one - no temp gauge only a warning lamp so I guessed the block sensor is for the lamp.

Engine run, disconnect sensor I just fitted and idle speed rises, reconnect and it drops in stages - sounds like I changed the wrong one.

Fingers crossed!

[Simon says]

Good luck with that

[100SRV]

Simon says said:

Good luck with that

You were correct Simonsays...what next?

[100SRV]

All fixed now - catalytic converter had failed so a new one of those and a replacement Lambda sensor were fitted. The car now has an MoT and is ready for a further 20,000 miles of commutin (I hope!)

thank you for suggestions!

100SRV