Failed MOT on emissions... help

[danger S3]

Hi everyone,
Sorry in advance for the long post. I'm having an issue with my 2001 S3 AMK, it failed it's MOT on emissions saying the CO levels were too high. Also my MPG had dropped from 27 to 24mpg at the same time the fault appeared:
Fast Idle Test:
CO - limit 0.3 - actual 0.77 (FAIL)
Lambda - limit 1.03 - actual 1.01 (PASS)

2nd Fast Idle Test:
CO - limit 0.3 - actual 0.21 (PASS)
Lambda - limit 1.03 - actual 1.05 (FAIL)

Natural Idle Test:
CO - limit 0.5 - actual 0.17

there is also a fault code:
16804 - Catalyst System Bank 1
p0420 - 35-10 - Efficiency Below Threshhold

That fault code started off with intermittent after it but after a week changed to the one above and then a week after that the engine warning light came on and that was the only fault listed.

It's still in the garage at the moment, there was a blowing from the front of the exhaust which turned out to be a cracked exhaust manifold, that's been replaced now and because the turbo seals had gone I got another from CR Turbos to replace that.

At the start of the year it had new cats and downpipe (oem equivilent). The garage have replaced the cats as a test to make sure they were not at fault but the fault remained so they have put the other ones back on. It also has a new Milltek cat back resonating exhaust. We were hoping that the fault was because of the cracked manifold but the exhaust is now not blowing from anywhere and the fault still remains.

The garage is going to try new lamda sensors tomorrow but they are not convinced it will fix the issue.

They told me they can hear the cam chain rattling a bit which probably means the cam chain tensioner is on its way out and there is some weaping around where the injectors go into the manifold, but we're not sure if either of them would cause that fault.

I have also tried giving it a good "Italian Valet".

The car got a new MAF about 5 years ago. and the car has done a total of 160k miles.

Anyone got any ideas for if the new lamdas don't fix the issue?

Cheers

 

[desertstorm]

As I was reading it I was thinking Lambda sensor. As they age the response slows and when they go faulty the kind of issues you are having now are present. The Italian tune up is always worth a go when cars have emissions issues.

 

[Gavin thyvhhh]

Find a new friendly tester
my s3 has never had a cat since I've owned it
Has straight through pipe
Like many people have



Sent from my iPhone using Tapatalk

 

[superkarl]

Your second test says pass on CO
First says pass on lambda.

Keep trying

 

[danger S3]

Thanks for your help guys, it has now passed it's MOT.
The garage doing the work replaced both Lamdas and then took it to their local test centre and it passed.
I went and picked the car up and took it to my local garage to get it's MOT retest done, it passed there too although they did say it took a while to get a good reading and they were worried it wouldnt pass, the CO was up at 0.6.
The garage that did the MOT still suspect the cats are at fault but the lamdas are now working, (they were faulty for sure)

Could the excess fuel getting dumped into the exhaust and the oil leaking from the turbo into the exhaust over the last few months damage the cats beyond the healing power of a good few weeks of 'spirited driving'?

 

[danger S3]

ok, another update
when driving with my brand new MOT and a smile on my face the 30 miles back to the garage to pick up the car i had borrowed from my old man the ****** engine light came on.
When i got home (after swearing a lot) i scanned it with VCDS and it was the same fault as before Catalyst System Bank 1 - Efficiency Below Threshhold.
I cleared the fault code and went for a drive but the fault never came back.
I called the garage this morning to see what they thought, they said the cats are 100% ok and that there is another problem with the car.

Is there anything i can do to try and investigate what the other problem clould be?
if the Injectors are scerwed thus dumping too much fuel in that's causing the high CO levels.
or what else could cause this?

stupid cars....

 

[superkarl]

What is the spec of the car?
Do some logs so the data geeks can have a look

 

[danger S3]

It's a standard(ish) AMK 2001
Only sort of non standard is the milltek resonating cat back exhaust.

What sort of things would be useful to log?

 

[Stuart B]

your EML error is 99% likely to be P420 it has a sports cat fitted hence the difficultly passing emissions - either keep clearing the fault or get it coded out next time its mapped. its normal for these cars once the exhaust is modified.

mine used to come on when sitting in traffic etc.

-- to be fair the changing of the lamda sensors probably didn't fix anything - they just heated the cat up enough to pass the MOT and charged you an additional 200 quid for new sensors.

your drop in MPG is more likely the sunny weather innit.. broom-tish

 

[danger S3]

Thanks for the reply Stuart but the car has not been mapped and it's oem equivilent manifold, downpipe and cats. It's just the part after the cats that's Milltek.

 

[Stuart B]

P0420 is the cat not up to temp within a timeframe = there are about 100 youtube videos about it. sounds like you have replaced the CATs (even if oem standard) - I bet they are not both 400 cel - they are maybe 200 cel

the original setup only has one post cat lamda sensor does your dual cat setup have 2 sensors?

https://www.youtube.com/results?search_query=p0420+catalyst+system+efficiency+below+threshold+bank+1

 

[Retroman]

High CO is usually either an overly rich combustion mix or faulty/failing cat(s). It sounds as if your post cat lambda sensor is suggesting the cat is not operating properly for some reason. If your combustion mix was wrong, the pre-cat lambda sensor would be switching like crazy and struggling to correct the mix and probably throwing a code. Decent garages should be able to observe all of this with their MOT/diagnostic equipment. If the pre-cat lambda is relatively inactive but you are producing high CO it is likely to be a faulty cat. I have experienced several aftermarket cats which have failed within 1 year (not on my Audi) and each time it was a high CO issue.

 

[danger S3]

Thanks guys, that's very interesting information. i didnt think of searching youtube, it ended up being a late night on youtube last night
My car has one pre and one post cat sensor. I hope they're not 200 cel cats, I'm betting it's sods law it wont say on the cats the model number.

This evening i tried to log the different sensors to see if i could narrow things down but i couldnt seem to find the correct blocks to measure.

I was having a look at these sites to try and determine what they all meant but wasnt getting the results i was expecting.

http://www.ross-tech.com/vag-com/m_blocks/
https://sites.google.com/site/1810martin/vcds-data-log

Any ideas which ones i need to log to check the pre and post lamdas and fuel trims?

 

[Stuart B]

there are a few threads (I think on VWVortex) with this P0420 error and on a totally standard car - it is often the aftermarket cat - I assume on my updated ECU they simply coded the threshold out to stop the EML - but I always got it after getting a 3 inch downpipe and 200 cel cat with a standard stage 1 map. some people manage to get a 100 cel cat through an MOT but mine took 10 minutes at 4000 rpm to get through. to be fair the amount of diesel used in vans and lorries towing stricken S3s nowadays the CAT hyrdocarbons are the least of peoples worries

 

[badger5]

Thanks guys, that's very interesting information. i didnt think of searching youtube, it ended up being a late night on youtube last night
My car has one pre and one post cat sensor. I hope they're not 200 cel cats, I'm betting it's sods law it wont say on the cats the model number.

This evening i tried to log the different sensors to see if i could narrow things down but i couldnt seem to find the correct blocks to measure.

I was having a look at these sites to try and determine what they all meant but wasnt getting the results i was expecting.

http://www.ross-tech.com/vag-com/m_blocks/
https://sites.google.com/site/1810martin/vcds-data-log

Any ideas which ones i need to log to check the pre and post lamdas and fuel trims?

031 is lambdas
001 is real time lambda adjustment
032 is adapted learned lambda offset

 

[danger S3]

Thanks again guys,

I logged those blocks out to a csv and had a look and i think it all seems normal, I've put a link to the csv file if anyone fancies a look, also if anyone fancies explaining it a wee bit, it would help me and might help others too

https://drive.google.com/open?id=0Bz362eoByRXIRlhtYm5nLVZEa3M

Please let me know if I've logged the wrong thing or if i should try logging something else.

Much appreciated.

 

[danger S3]

Time for a wee update,

So, I took the car to Bradbury Motor Group in Prestonpans to get the injectors serviced as part of my investigation into why the fuel economy had dropped a lot, they came back and said two of the injectors would only just pass and two of them were screwed and letting in a lot of extra fuel, they uploaded a video of my injectors on the test rig which you can see here, They were really good and helpful.https://www.youtube.com/watch?v=8cjLm4wH3n8



So the result was they were beyond servicing, so I got 4 new injectors and it made a huge difference to my mpg, on the longish motorway drive to the garage I got 29mpg, driving home with the new injectors I got 35mpg.

Anyway back to the p0420 code, it still keeps coming back and the CO emissions are still too high.

I don't think there's anything else it can be apart from the cats, the garage that fitted the cats at the start of the year told me recently that they are 200 cell cats but insist they're still ok. They also offered to map the code out.

The thing that's confusing me is the fault code didn't appear for the first 3 or 4 months the cats were on, could excess fuel from the dodgy injectors and oil leaking from the old turbo have broken the cats in a few months?

I'm now at the point where I'm going to get a price for genuine cats, and make sure I'm sitting down at the time

 

[Stuart B]

just code it out and enjoy your car mines out of MOT - I am looking for some tarp

 

[danger S3]

yeah unfortunately my brain wont let me just code it out.
It doesnt really matter if the fault code is coming back or not, the CO levels at an emissions check are still too high, 0.6 rather than below 0.3

There is something wrong with the car, just need to find out what it is.

 

[mrsingh2u]

looks like cats are failing... could use this as a good time to swap downpipe and cat out for something better, if you currently are running stock downpipe and cats - funds permitting of course...

 

[Stuart B]

I think they have already changed the downpipe and cats - but used standard dual twisting downpipe and dual cats rather than 3 inch DP and single cat.

 

[danger S3]

ok, so I now have not p0420 fault code
Iit looks like it was the CATs, i got a guy to have a proper read of all the sensors and confirm that there was nothing else that he could see that could be causing it and also that there was nothing else that would damage the new cats.
then i just forked out for new OEM CATs.

he was saying that pre 2004 the after market cats dont need to comply to some standard and thus are just a bit pish.

so to fix one wee fault code all i had to do was:
replaced exhaust manifold that had a crack in it.
replaced turbo because the seals had gone and oil was getting dumped into the exhaust.
replaced the injectors as they were sticking open a bit and dumping too much fuel in. (combo of the oil and extra fuel probably pushed the rubbish cats over the edge)
2 x new lambdas
I also replaced the rest of the exhaust at the time because it was on its last legs, at least i now have a new block back exhaust system.

Thanks very much to anyone that helped out with advice and suggestions.

 

[Stuart B]

blimey - well at least you don't have the error any more and a new exhaust pipe