Hi
Took the wife's Punto (98/R) Mk I 1.2 16v Sporting in for an MOT yesterday. Noticed last week that the front section (down pipe) of the exhaust was blowing and lack of power, so bought this section. Gave it to the MOT garage at same time, asked them to fit for me and carry out MOT. Car failed, but only on the emissions. Basically the chap said that the co2 was reading high/the hydrocarbons were extremely high but the lambda test was fine. Car sounds as if it is running on 3 cylinders, very lumpy and got to say that I did sense it was using more fuel last week, strong petrol vapors etc. They cant look at it til next week. I suggested lambda, but they said it passed the test. Also, have never managed to change 1 x spark plug in last 3 years as it is basically solid in there!! They will try to see if it is possibly this next week. Not sure if a dodgy spark plug/old plug would cause these massive emission readings? Not likely to be the front pipe they have fitted that is letting in air? Really grasping at straws here as I could spend money on (a) plugs, (b) HT leads (c) lambda sensor (d) filters (oil,fuel) or even worse (e) new cat??!?? Any advise you can give guys is very much appreciated. By the way, have noticed that the oil level is below the min on the dipstick, so will be replacing/topping up today but doubt it could be that? Cheers

Anything other than looking at codes is a waste of time until that plug is replaced.

Presumably the garage have put a scanner on the ECU and read the lambda switching trace

Ask the garage to get the plug out and you'll have a chance. Running with an ancient plug will have heavily stressed the catalyst. It may well have given up.

Many thanks for your response. Not sure what the garage did to check, other than told me that the co2 emissions were high/lambda was ok and the hydrocarbons (which they said should be no more than 200) were almost 1,000!!! They will take the plug out on Thursday and see what happens. Actually, it is plug 3 and 4 that are both 'stuck' there. I took off the HT leads one at a time and on each time the engine running changed (for the worse), so I assume the HT leads are ok? But, as you said, not much point in spending more money until they have checked and replaced the plugs. If it does end up being the cat, where is best price on the internet? Also, is there any simple check I can do with the cat? Thanks again !

One coil drives plugs 3&4, the other coil drives 1&4. If one plug is fouled it can stop both on that coil from sparking. They must all be renewed at the same time.

If you are not confident with those stuck plugs leave it to a good mechanic. If a plug shears off, the cylinder head will have to be taken off to remove the broken plug.

Thanks again for your sound advice. Yes, will definitely leave it to the mechanics to sort for me! Fingers crossed that this is the problem. Will keep you posted.