Emissions Failure - Help!!!

[marleyp]

Hello,

Had my car MOT'd today and it has failed on CO emissions. can anyone shed any light on why, before I start changing things.....

A6 2.4 auto 1998 (AGA Engine). No faults found using VAG-COM??

Fast idle Test
CO level = Fail 3.81% (pass 0.3%)
HC = pass 142ppm
Lambda = fail 0.90 (pass 0.97 - 1.03)

Second Fast idle
CO= 4.34% fail
HC= 185ppm pass
Lambda= 0.88 fail

Natural idle Test
CO= 5.35% Fail (pass 0.5%)


Any help on this would be gratefully appreciated

Cheers

[paul b]

It might be the lambda sensor. This fault has been known to happen these days.
Paul

[lonky]

Provided you have new plugs & air filter, lambda sensor would be a good next bet.

If you have vag-com you can watch each of the sensors.

You can also check if either bank has fault codes.

The MOT just takes an average of both banks, so one side could be perfect while the other is bad.

lambda sensor normally effects your CO, while the CAT looks after the HC.

[marleyp]

Thanks for the info....

I think you are right. I have bought a CO tester and the next thing I need to check out are the Lambda outputs on VAG Com. I'm sure there are 2 of these on my car, but not sure??.. need to check that one out. I also have the workshop manual with all the Factory settings required.

I'll post more info when I try it all out, won't be this weekend as it is ******* down, probably next.

By the way got a price for 2 Cats - £650 + Vat from local dealer.

Best price I found however was on www.buypartsby.co.uk , £175 inc VAT

Cracking price..eh

Cheers

[lonky]

I paid £103 inc vat for one of my CAT's - 2.4 V6 AGA

Try this site
http://www.cats-direct-shop.co.uk/

or
http://www.europeanexhausts.co.uk

I got mine from eurocats, they supplied the wrong one to start, so make sure you measure the length of your exhaust before buying, saves swapping it !

Best way of changing is to jack up one side only of the car. I used a big ramp at the front and a smaller one at the back.

To undo the lambda sensor it is best with the exhaust undone so you can get the angle for the spanner by moving the exhaust. - Best with 2 people though I did it on my own.


You have 2 lambda sensors not 4. each one is next to the flange by the engine in front of the CAT.

A few years later they put one after the CAT as well.