Emissions - is there any way to fix this?

[squiggers]

Hi there,

I'm writing in the hope that someone might be able to shed some light on the problem I have:

I have a '96 Megane RT and I've been at the NCT (that's the Irish equivalent of the MOT) four times since November and every time it failed on the emissions. To combat the problem, I have had:

- a new cat fixed
- a new lambda sensor fixed
- petrol tank cleaning liquid put in the tank
- a new back box installed
- the air filter changed

Now only the low idle emissions seem to be the problem. All readings were fine as I left the garage last time but by the time I got them tested at the NCT centre just a couple of hours later, the high idle emissions and the lambda readings were OK but the low idle CO levels were up at a whopping 3.47 vol % again (the limit for my car is 0.5 %).

My mechanic doesn't know what to do. He rang the Renault guys in Dublin and they couldn't give him any pointers either. I rang an emissions specialist and he said he is having a Megane coming in sometime soon that seems to have exactly the same problem - it's been to various garages and all standard things have been looked at, still the emissions are fluctuating arbitrarily. He said he hadn't come across something like that before and he'll have to experiment.

Would anyone have any suggestions at all? I've only had the car for a few months and didn't see this coming as it is otherwise running perfectly!

Many thanks,
Squiggers

[AlexB]

Read this first:
https://meganedoksi.uw.hu/MEGANE_I/MR312MEGANED.PDF
https://meganedoksi.uw.hu/MEGANE_I/MR312MEGANE1.PDF

I suggest to start testing with simple things -- check the condition of the spark plugs. They may tell you an interesting story... How high is oil consumption?

[mintyman5]

could try forte petrol treatment , worked a treat when my old laguna had high emmisions , also check the testers are getting the engine up to full working temperature before taking the readings , its a requirement in uk i believe

[squiggers]

Thanks, AlexB and Mintyman5, I very much appreciate your help!

[Deano16v]

give the car a good caining before you put it in for the NCT, if the CAT has a lot of heat in it the car will run more efficiently. also check your other sensors that would affect the fuel mixture, the Lambda has already been changed so check things like the CTS (coolant temp sensor). if thats faulty then it the ECU could be chucking too much fuel in.
I'd change the plugs, check the sensors, run a whole bottle through of the forte additive and then give it a go.

[AlexB]

It is not just about changing the spark plugs. The condition of the spark plugs indicates the condition of the cylinder-piston group and valves with valve stem seals. Don't forget that it's a 96 car!

If there is any oil on them, the next step will be to check compression.

[squiggers]

Thanks guys,

I'll run all suggestions via my mechanic and let you know how I got on!

Regards,
Squiggers

[squiggers]

Hi there,

I managed to pass my NCT...finally! Although my emissions still seem to fluctuate. I got my sparkplugs changed and more tank cleaning stuff mixed with the petrol - the CO levels read fine at the garage yet lo and behold, at the test centre both my high and low idle emissions were too high again. I then told the NCT guys what had been done to the car in order to fix the problem and said that the mechanic doesn't know what else to do; they took mercy on me and said they are going to test the car at a different lane...and it passed there.

So, unfortunately the problem still hasn't been solved but at least I do have my NCT...

Thanks for all the replies!

Regards,

Squiggers