MOT emissions

[ian974]

Hi guys,

Car has failed its MOT emissions test and I'm not sure what will help it.
Lambda readings from 0.98 to 1.09 and passed, but high HC and CO readings - CO up to almost 6% at idle but came down to 3.96 then 1.24 on fast idle test. HC readings were 765-593. It did get warmed up for the test!
No apparent vacuum leaks, fan appers to be working at the correct temperature and temp senders were replaced about 2 years ago. Engine drives fine, though can be a little lumpy at idle at times.
Cataytic converter is only a year and a bit old, but a cheapy so wouldn't be tooo suprised if it's past its prime already, but would like to check if theres any other other usual suspects to try rather than replace it with a decent one and have it knackered again for next year.
Bar trying some redex and swapping sensors I'll probably end up sticking it back to the garage I think!

On the bright side though, other than that it had a pretty clean bill of health!

[robin]

If it is lumpy at idle & you get high HC/CO readings then that implies misfires which are allowing unburnt fuel into the exhaust.

If it idles cleanly then it sounds like it is overfuelling which might be the inlet air temperature sensor, the throttle position sensor or perhaps one injector being a little clogged causing the ECU to add fuel to get lambda correct (the weak cylinder will be pumping O2 into the exhaust, a bit like an air leak in the exhaust pipe).

Is it S1 or S2?

Cheers,
Robin

[ian974]

Its an S1, standard engine.
I have a spare inlet temp sensor and a couple throttle position sensors, though not brand new, I could swap them and see what difference they make to things.
Is there anything that can be checked regarding the injectors?

[SAJ]

I always make sure the car has been serviced before an MOT even if it is just an oil and filter change. Stick this stuff in, works wonders for getting cars through emissions test: http://www.camskill.co.uk/m1b13s4323p53 ... 0ml_/RS_GB

Don't use redex - pile of crap that screwed my mates Audi engine a few years back. Forte is used by most good garages and really does make a difference.

[LotusLee]

for Forte, have used it a couple of times to get the Golf through MOTs, usually just put it into 1/4 tank of fuel.