gOOOOran

Hello,

Just popping over from the Tyresmoke forums to ask a question.
Is it possible, without getting a new ECU chip, to re-program (using ROSS-Tech?), or trick the ECU into ignoring the second set of Lambda sensors (the ones after the cat) so I can remove them completely and install a pair of sport-cats?

sorry, forgot to say, its a 2001 S8, so 4xlambda sensors unfortunately.

My understanding is if I leave the post-cat lambdas in there, because of the improved flow of the sport-cats they will think the cats are failing and the ECU will register a fault code.

diogeniS8

I have never seen a chip for our car, and I doubt you can VAG the ECM to make the changes you need.
But if you must install the high flow cats use some black electrical tape to cover the CEL.

jazbo123

try to install a default siganl for the post-cat sensors. The rear sensors are really to monitor the health and function of the cat-converters, and they generate a much more stable signal than the front ones (assuming the cat is working). Substituting a regulated 500mV signal could elimiate the rear sensors with a little tweaking and work without setting the CEL. There might be more involved since another circuit might be checking the heating elements for proper continuity, but in theory, resistors could also substitute for that.

Overall, probably not worth the hassle!

jazbo123

Sounds like it works. Easier than my solution ;-)

pkrasusky

duno - BUT - puleese report back to us HERE your findings thanks good luck

gOOOOran

Thanks guys! That was quick!

I like the Wayne Angle solution best. I have found a similar solution here on audiforums which uses sparkplug anti-foulers, it was this post:
https://forums.audiworld.com/tt/msgs/1393818.phtml

If I was a bit more confident at electronics I may even try the resistor mod, as that way I can get rid of those pesky lambdas altogether.

I guess the ultimate option is chipping, MTM or AMD or Superchips, I guess they can make the chip so that it doesnt use a signal from those secondary lambdas at all so they can just be disconnected.

For now I'll try the Wayne angle, I'll let you know how I get on.

Cheers!<ul><li><a href="https://forums.audiworld.com/tt/msgs/1393818.phtml">https://forums.audiworld.com/tt/msgs/1393818.phtml</a</li></ul>

CalG

To replace a "missing" O2 sensor.

tozoM8

You can install pre-cats for an 02' or 03' A8.

sutherland

I answered this on Tyresmoke, but I'll answer here as well because I asked the question on here a couple of months ago and nobody had an answer.

I have switched to highflow 200cpi cats on my 02 S8 which has post-cat sensors and so far all is well--no CEL lights. I wouldn't like to guarantee that 100cpi cats would not cause a CEL.

At £400 fitted for two cats it was massively cheaper than the near £2000 Audi were quoting.

gOOOOran

I put the Wayne Angles on the pipes, now over 400 miles later all is well. No CEL light even though they are 100cpi cats. Two thumbs up for Wayne Angle!

However, I still want to remove the rear lambdas completely if possible. Just have to find out if there is a valid ECU code for Euro II emissions for the S8.