NCT Emmissions Question

richardw001

Looking for some quick advice:

Okay car is 01 Megane - Just failed NCT The Exhaust Emission results were as follows:

Engine/Oil Temperature 89 degrees celsius

Low Idle CO 0.49% vol
(1070 rpm ) HC 261 ppm

High Idle Lambda: 1.01
(2720 rpm) CO 0.49% vol
HC 112 ppm


Only Fail on the report is beside "above 0.30%" - FAIL/REFUSAL
Everything else says PASS or N/A

My question is - is this a big deal or a small difference that should be fixable cheaply (or can someone tell from this ?)

We've just put a new timing belt in it so wondering whether we are facing another big bill or new car scenario ?!

Thanks in advance.

1. Does the engine use lots of oil? 2. Did you notice any performance difference before and after the belt job?

If answer to both of the questions is "no" it looks like the cat may have had it, I'm afraid.

PS. Looks like the NCT tester tried to help you by raising the idle to 1070 rpm to make the low idle to scrape through.

Chimaera

Yey, another emissions thread (/me thinks we need a sticky on this at this stage).

So you've failed on CO and HC. Excessive CO results from poor combustion which would be backed up by increased HC levels also. This can be from a few things.

Poor fuel atomisation: any idea how well the fuel injection system is performing? A 13 year old car could have carbon deposits around the injectors at this point, so a good quality injector cleaning fuel additive might be worth a shot along with an Italian tune-up.

Poor ignition: when were the plugs changed last? If they're old/worn, the spark won't form properly and it'll take longer for the fuel to ignite, meaning it won't burn completely within the time window available during the engine's operating cycle.

These two are the cheap DIY fixes and probably worth a go regardless of what else you do.

Lambda or MAF sensor failure: the lambda sensor reports back to the ECU on the level of combustion achieved (by measuring remaining oxygen levels) and comparing to what entered the engine (measured by the Mass Air Flow sensor). This allows the ECU to control fuelling to keep emissions in check. If the sensors are faulty, the ECU doesn't have this feedback and reverts back to a default map which will be suboptimal.

Solving this problem will require some diagnosis (that doesn't just involve buying parts and swapping them blindly). If you know what you're looking for you can do this yourself, otherwise I'd suggest a good mechanic who knows these cars.

Another possibility as Samih pointed out above is that the engine is burning oil. Has your oil usage been high recently? If this is the case, there's not a lot to be done as this results from worn cylinders or piston rings. You're into rebuilding the engine with new rings and possibly pistons to correct this and that's an expensive job.

Chimaera

Chimaera wrote: »

Another possibility as Samih pointed out above is that the engine is burning oil. Has your oil usage been high recently? If this is the case, there's not a lot to be done as this results from worn cylinders or piston rings. You're into rebuilding the engine with new rings and possibly pistons to correct this and that's an expensive job.

Spot on. I also asked about the timing belt as incorrect engine timing would increase emissions too.

richardw001

Thanks for the responses - I guess the answer isn't clear without diagnosis (well thats what I take away from youre all saying) - However at least I know now that the difference isn't so low or high (from the pass marks) that its clear cut that its going to cost loads or is something small (if you know what I mean!)

I hadnt even considered emissions to be honest as it was fine in the last NCT - so it would have been cold going in and had no prep work regarding that (last service was about 2 months ago)

The next plan is for it to go to a fairly decent mechanic - so I'll let you know then.

Just as an aside - an NCT sticky would probably be a good thing - so that it doesn't clutter up your forum !

Thanks again for your replies.