Nct emmisions fail
 

Hi all.
My1996 4.2 v8 a8 fail the nct/mot today on its emmisions.. Again... It failed previously on this and the exhaust was leaking so had part of it replaced and now the readings are even higher. Shockingly high. Now it'll be going back to the garage next week but I suppose I'm just looking for ideas...
Readings are below. These are today's readings.
Low idle:
Co 6.63 vol above 0.50 %fail
Hc 234ppm

High idle
lambda 0.82. Not between 0.97 and 1.03
Co 6.63 above 0.30%. Fail
Hc234 ppm. Above 200ppm fail


Any ideas?
Thanks

Just for info, my car recently passed the MOT test (facelift edition, model year 2000 A8L) with the following figures:

HC (limit 200) - reading was 46 ppm vol
Lambda (limit 0.97-1.03) - reading was 1.006

That's running quite rich. Any fault codes stored in ECU? My guess would be there is an air leak in exhaust system not far from lambdas letting fresh air in, lambdas read it as lean and ECU then chucks in too much fuel.

I was told that there's no codes in the ecu, and they welded in new pipe before the cats... Hopefully they've made a mess of it and that it's just that... Fingers crossed but your right does sound like it's running super rich...

Could also be the lambda sensors reading lean so the ecu is over-fuelling. Try unplugging them as a diagnostic step as the ECU will just run open-loop using the MAF. If it improves the reading then replace the sensors. If not, look elsewhere :)

Great thats a start... Will try that 1st....
Thank you.

Just following up here. Have replaced left bank o2 sensor as it seemed dead according to the diagnostic in the garage and after a smoke test 2 breather pipes from the inlet manifold were split open.
After that the emmisions in the garage recorded fine, so nct retest Tuesday... Fingers crossed.

Passed retest... Was the above. Whoop whoop!