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Goz

can post-cat lambda sensors be removed?

24 posts in this topic

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

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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

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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

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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

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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.

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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!

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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.

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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.

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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.

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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!

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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?

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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.42draftdesigns.com/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.

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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.

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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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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.

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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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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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Goz

This info should also be on the sticker inside the service book or the spare wheel well.

Aren't the angle block things working for you? I just got mine from Wayne and had them fitted yesterday.

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Hi Sutherland,

Wayne's blocks are working just fine, I kept the trip meter on, so far over 400 miles with no CEL and thats on 100cell cats.

I want the damn things (lambdas) removed because I want to put more silencers in after the x-pipe, the car drones at 1600 - 2000 revs at the moment, and if I can get rid of the lambdas perhaps I can have standard silencers fitted rather than custom ones. Also, I like the idea of simplifying the car electrically, so when the rear lambdas fail I wont have to replace them, I hear they are expensive. Also I just dont like the idea of anything cat-realated, if I could remove the cats too I would have.

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Sorry Tobes, I got the trans code wrong. I looked in the service booklet as Sutherland suggested, and sure enough there is a sticker in there:

Engine Code: AVP

Trans. Code: EUU FBG

Model Year: 2001

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