Failed NCT due to high emissions

slave1

Hi all,

My 98 Megane Classic just failed NCT because

a. my back reg didnt have the county name in Irish :rolleyes:

b. emissions were 2 high
low idle 720 rpm
high idle 2860 rpm

I'm not car mechanically minded and my mechanic has said about 450/500 for a new cat. Reasonable??

Can someone put plain english on the emission results, what they should be and possible reasons why they are so high

As a matter of interest I have no problem making my car acceptable, I just want to understand it all

Cheers

mike65

If your car has a cat the emmissions are ultra-low, once the cat goes its an instant fail. The joke is that your car may still have had lower emissions than a car without a cat like mine.

The price mentioned sounds about right.

Mike.

echomadman

You're not giving enough info on the emmisions there, those are just the engine rpms

mike65

As echomadman says post the actual emmision numbers.

My non-cat Merc did the following - @ 810 rpm.

HC (hydro carbons) 308ppm

CO 0.15 volumn %

Mike.

slave1

Okay, the missus dropped the car off and I didn't have the info to hand when I posted thread, I actually have the previous results too
FYI this is a well looked after car, I don't rally drive and am not a speeder, mostly shortish trips (under 6 miles), 1.6L petrol, manual gearbox, the car was well under in all other categories

2002 results
Oil temp 70 C
Low Idle (1440 rpm) CO 0.02vol% HC 0ppm
High Idle (3170 rpm) Lambda 1.003 CO 0.02vol% HC 23ppm

yesterday's results 2 years/15k later
Oil temp 82 C
Low Idle (720 rpm) CO 0.81vol% HC 0ppm
High Idle (2860 rpm) Lambda 0.958 CO 1.59vol% HC 61ppm

Gmodified

very poor emission result for car that age. looks like Renault and Citroen have enough problems with the emissions.

I know guy with Citro Xantia which required major surgery to pass NCT car was relatively new but :

-computer had to be changed( known issues as fuel management contributed to bad combustion)
-valve guides had to be replaced
- cat was replaced

car barely passed NCT

Auslander

Hey slave.

Its quite common for cats to give up the ghost usually at @ 10 year mark

By the sounds of what you've described,
I say that more than likely its all the short trips that have done
the damage.

The engine never has time to reach normal operating temp,
the fuel mixture is always running rich.

In laymans terms all the unburnt petrol in the exhaust gasses
are passing through the cat, killing it.

This is also the reason why it is not recommended to push start cars
with a cat, since the unburnt petrol in the downpipe (exhaust) can also contribute
to premature cat failure.

Paddy