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can post-cat lambda sensors be removed?


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#1 Goz

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Posted 07 March 2009 - 11:03 PM

Hi,

I have decided to get a custom exhaust, I was also hoping to get some high-flow cats fitted at the same time but it turns out I have pre-cat and post-cat lambda sensors :flush:

What are the post-cat lambda sensors for, and more importantly can I get rid of them? Is it as easy as telling the ECU to ignore them using VAG-COM?
Has anyone done this before?

Thanks

Goz

#2 A8_Tony

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Posted 08 March 2009 - 07:27 AM

Not sure on this one fella.

There are a lot of people out there who've had custom exhausts fitted. Myself included. Who haven't worried about any sensors after the cat. What year/model is yours?

Tony

#3 Goz

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Posted 08 March 2009 - 10:24 AM

Hi Tony,
Its a 2001 S8. I asked a few places and they all said you can have the high-flow cats, but you will need a re-map because of the lambda sensor after the cat. Its a lot of money to do a new exhaust, sport-cats and remap all in one go. So I was hoping maybe there is a way to disconnect these lambda sensors without needing a re-map. then I can get a re-map later if I want it.

Thanks

Goz

#4 A8 Doc

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Posted 10 March 2009 - 03:10 PM

Or you can use spark plug extenders to mount them further out of the exhaust which works a treat.

The americans love 'em.

#5 A8 Doc

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Posted 10 March 2009 - 03:11 PM

Or you can use spark plug extenders to mount them further out of the exhaust which works a treat.

The americans love 'em.


Here ya go the idea:

How to install the spark plug anti-foulers to remove the ses or cel light - evolutionm.net

#6 Tobes49

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Posted 10 March 2009 - 07:59 PM

Depending what ECU software the car running, You might be able to recode it to a 2 probe system. I did this with my S4 engine.

Get someone to check with VAG-COM if you can recode the ECU to EuroII standards

#7 sutherland

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Posted 11 March 2009 - 08:13 PM

I asked about changing to sport cats on various forums, but didn't get any responses to my queries about the effect on post-cat lambda sensors, so I've decided to go ahead and get them fitted to my 02 S8 anyway and see what happens. I was told the same about remaps, but the exhuast place said they've done it on other 4.2 Audis with post-cat probes and it hasn't caused CELs. I am getting this done tomorrow so I'll report the results.

It would be good to find out about recoding the ECU in case that is necessary--I do have VAGCOM.

#8 Goz

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Posted 11 March 2009 - 10:00 PM

Thanks guys, good info. I'm really hoping I can re-code it to a 2-probe system like Tobes suggested.
In the meantime I'm going ahead and fitting the high-flow cats anyway like Sutherland. I'm booked in for Monday.

I have also done some searching and asked the guys over on AudiWorld.com they came up with the spark-plug extender as well, but also this one:

VWvortex Forums: DIY: Wayne Angle O2 Sensor Block
42 Draft Designs

which I have gone ahead and ordered. but if I dont get a CEL, I'll be even happier.
Sutherland let us know how you get on with your cats.

Also, just to confirm, even if you get a CEL from the post-cat Lambdas, it doesnt affect engine running at all? They just monitor the operation of the cat?

Cheers!

#9 Goz

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Posted 11 March 2009 - 10:04 PM

Here is the spark plug extender / anti-fouler post from AudiWorld forums incase its usefult to someone.

AudiWorld Forums: possible solution for those running race cats or test pipes (provided by gesTTalt)

#10 sutherland

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Posted 12 March 2009 - 05:25 PM

Well, I've now got two highflow cats on my car (200cpsi not 100). So far it's going perfectly and the CEL is now staying off. It's also going more smoothly and sounds a lot better, but there's a reason for that--when he removed the left cat he discovered it had been smashed out so one side was de-cated. The noise I was hearing was therefore not a rattly cat, but an empty one resonating in a rather unpleasant rasp. I imagine the uneven backpressure may not have been helpful either.

#11 Goz

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Posted 13 March 2009 - 09:23 AM

thanks Sutherland, thats good news. Unfortunately I went over the top and bough 100cpsi cats, so I'm still a bit worried. I need to get myself VAG-COM soon.

#12 sutherland

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Posted 13 March 2009 - 11:33 AM

Perhaps even the 100cpsi will be OK--the CEL was not coming on immediately in my car even although the cat on bank 2 had been smashed out by some villanous traders in London.

#13 Goz

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Posted 13 March 2009 - 09:05 PM

good point! i didn't consider that. perhaps these post-cat lambdas are quite insensitive. Fingers crossed, will let you know when the new cats are in.

Cheers!

#14 sutherland

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Posted 16 March 2009 - 08:05 AM

Perhaps I replied too soon. The CEL came on yesterday and VAG-COM gave fault of emissions beyond threshold for both cats, so it doesn't like 200cpsi cats either.

I reset and since drove 40 fairly hard miles and so far they haven't come back on, but I guess they will. How do I recode to Euro II standards? I can't find anything precise for an S8 on the web. Does this affect other things like fuelling?

#15 Goz

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Posted 20 March 2009 - 05:47 PM

Hi Sutherland,
I ordered a couple of these cat blocks 10 days ago from the US ($78 in total inc. shipping). They arrived on Thursday so I took them down to Hayward&Scott and they fitted them on whilst they where working on the exhaust.
I picked my car up today from H&S, the exhaust is done and is really nice (sorry, forgot to take pics in all the excitement), I drove back home (about 35 miles), and so far no CEL light. Maybe its too soon to be sure, or maybe these cat-tricking blocks really work, I'll let you know if anything changes.

Here is the site:
http://www.42draftde...om/faq.htm#test
basically you just email wayne92SLC@yahoo.com he makes them himself, he replied really qickly, within a few hours, and it only took 8 days for them to arrive.

Although I would first see if someone with VAG-COM can have a look and see if your car can be programmed so it doesnt need them, thats the best and cheapest option in my opinion and as soon as I can get hold of a VAG-COM I'm going to do the same.

good luck.

#16 sutherland

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Posted 23 March 2009 - 09:49 AM

Thanks Goz. I've actually got VAG-COM, but I cannot find adequate information on how to reprogram for a different emissions standard or to make it ignore the post-cat probes. Any help would be appreciated.

#17 Goz

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Posted 01 April 2009 - 06:42 AM

Hi Tobes,

I got a copy of VAG-COM, and had a go at finding the emissions settings. I went into Engine > Coding and Engine > Basic settings, unfortunately I dont have a clue what I'm doing. Perhaps naively I was hoping there would be a field labeled 'Emissions'. Am I looking in the right place, what should I look for that would indicate Emissions can be re-coded?

Many thanks

Goz

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#18 Tobes49

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Posted 07 April 2009 - 12:35 PM

Hi Tobes,

I got a copy of VAG-COM, and had a go at finding the emissions settings. I went into Engine > Coding and Engine > Basic settings, unfortunately I dont have a clue what I'm doing. Perhaps naively I was hoping there would be a field labeled 'Emissions'. Am I looking in the right place, what should I look for that would indicate Emissions can be re-coded?

Many thanks

Goz


Can you please post your: Car year, Engine code and gearbox code

the recode screen is the correct place but I cant match your coding.

#19 Goz

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Posted 07 April 2009 - 10:24 PM

Hi Tobes, thanks very much for helping me out. I almost changed the code to 05753 without checking if its valid (would it have done any harm even if it wasnt?)
I think I found the engine and trans code by going into the adaptation screen:
Model Year: 2001 (S8)
Engine Code: AVP
Trans Code: LBL

Extra info (VIN + something else?): WAUZZZ4DZ1N011123 AUZ7Z0Y1748242

Cheers!

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#20 Goz

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Posted 07 April 2009 - 10:47 PM

sorry, just realised, LBL is the file type extension, not the trans code, doh!!
I will have a look for the trans code tomorrow.




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