A8 Parts Forum  

Go Back   A8 Parts Forum > A8 D2 > D2 - Fuel and Exhausts

D2 - Fuel and Exhausts Everything to do with getting fuel into the engine, and fumes back out again

Reply
 
Thread Tools Display Modes
  #1  
Old 28th July 2019, 02:20 PM
jt racing jt racing is offline
Member
 
Join Date: Oct 2015
Posts: 67
Default 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
Reply With Quote
  #2  
Old 28th July 2019, 03:02 PM
johnny_quattro's Avatar
johnny_quattro johnny_quattro is offline
Senior Member
 
Join Date: Sep 2012
Location: Wallington, Surrey
Posts: 555
Default

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
__________________
2010 B8 S5 Sportback quattro 3.0 Supercharged in Sprint Blue (current girlfriend)
2000 D2 A8L quattro 4.2 in Audi silver (my ex-girlfriend)
Reply With Quote
  #3  
Old 28th July 2019, 05:17 PM
ainarssems ainarssems is offline
Senior Member
 
Join Date: Aug 2010
Location: Rushden, Northants
Posts: 3,799
Default

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.
__________________
Currently 8less
2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D

8 history:
2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
Reply With Quote
  #4  
Old 28th July 2019, 05:41 PM
jt racing jt racing is offline
Member
 
Join Date: Oct 2015
Posts: 67
Default

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...
Reply With Quote
  #5  
Old 28th July 2019, 05:57 PM
MikkiJayne MikkiJayne is offline
Senior Member
 
Join Date: Jan 2012
Posts: 5,017
Default

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
Reply With Quote
  #6  
Old 28th July 2019, 07:38 PM
jt racing jt racing is offline
Member
 
Join Date: Oct 2015
Posts: 67
Default

Great thats a start... Will try that 1st....
Thank you.
Reply With Quote
  #7  
Old 8th August 2019, 09:00 PM
jt racing jt racing is offline
Member
 
Join Date: Oct 2015
Posts: 67
Default

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.
Reply With Quote
  #8  
Old 14th August 2019, 08:35 PM
jt racing jt racing is offline
Member
 
Join Date: Oct 2015
Posts: 67
Default

Passed retest... Was the above. Whoop whoop!
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 02:07 PM.


Powered by vBulletin® Version 3.8.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.