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

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  #1  
Old 28th July 2019, 02:20 PM
jt racing jt racing is offline
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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
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  #2  
Old 28th July 2019, 03:02 PM
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johnny_quattro johnny_quattro is offline
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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
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Old 28th July 2019, 05:17 PM
ainarssems ainarssems is offline
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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.
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  #4  
Old 28th July 2019, 05:41 PM
jt racing jt racing is offline
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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...
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Old 28th July 2019, 05:57 PM
MikkiJayne MikkiJayne is offline
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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
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Old 28th July 2019, 07:38 PM
jt racing jt racing is offline
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Great thats a start... Will try that 1st....
Thank you.
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Old 8th August 2019, 09:00 PM
jt racing jt racing is offline
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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.
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  #8  
Old 14th August 2019, 08:35 PM
jt racing jt racing is offline
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Passed retest... Was the above. Whoop whoop!
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