aTOMic

I think I need to do both "upstream" or "pre-cat" sensors. Bentley says it's necessary to remove the intake manifold. I wondered if it's possible to avoid this, since I'm a lazy American

Precious little info here and hard to search since it's variously called O2 sensor, Lambda probe, Oxygen sensor, B1S1 & B2S1, as well as HO2S and G108; but I am an eternal optimist.

TIA,
Tom

ohsigmachi

I have exactly the same question and concerns! It is surprisingly hard to aggregate the info through the search function and google is worthless since you have to wade through 11 million different parts houses trying to sell you an Oxygen sensor.

aTOMic is yours a 4.2l?

Mine is an '05 quattro base and I want to change out all four.

aTOMic

Yes, 4.2 "PETROL" as opposed to the 4.2 diesel offered in Europe; you can go to Google Advanced search and limit searches to Audiworld.com or A8parts.com, or use the "-shipping" in your search to almost eliminate shopping/ad results; but you'll see there is not a lot of info. I'm afraid there is no way to do it without removing the manifold.

halik

Ooooh clever! Google has been getting crazy spammed lately.

aTOMic

Has anyone done the pre-cat sensors (DIY) - even going by the book and removing the manifold - that can provide me any tips?

PaulW

I can tell you that you can do both pre-cat sensors on a D2 A8 40v motor from the top of the engine bay. You just need a good O2 sensor wrench and some patience.

aTOMic

Thanks Paul!
Does the D2 manual procedure call for removing the manifold?

What do you mean by "Good" wrench... crowfoot, flex/wobble extension, or just the socket with the slot for the wire?

On the D3 I cannot even see the left one even with all the vac and other hoses d/c'd... but I have not removed the main intake hose I confess...

Thanks again,
-Tom

MP4.2+6.0

PaulW is presumably right on the D2's. Same thing on my 2000 A6 4.2; I did both sides with basically everything in place, essentially up on top of the intake crouched under the hood reaching down. Pretty much done by feel/blind.

BUT, this knowledge may not be transferable to the D3. It's why I didn't respond earlier. Plus, obviously w/ a W12 it's different. Smog regs changed after 2003 in the US. It basically forced Audi to move the first cats up close in to the head instead of way downstream like they used to be. It's why there was never a 2004 RS6 in the USA, even though they shipped more in Europe. Thus, I expect the D3 4.2 to be like that since they would have complied it to the newer rules, and then probably change the O2 set up and exhaust manifold some.

If you search over on QW D3 board BTW, one guy says he did it w/out pulling the intake manifold. No details in the post though. Having pulled my C5 4.2 manifold a few times, I don't think it's that big a deal either, plus a chance to check things out more carefully--valve cover gaskets, oil vapor system, intake multistage vacuum system (prone to gumming up over time), etc. From my C5 4.2 experience, issues will likely be found among this stuff as car gets to 100K. Having pulled my W12 intake recently to get to the spark plugs, it was also easy--maybe more so than my C5 4.2 at the margin.

aTOMic

Thanks for the reply, MP. I decided to quit being such a whiny baby and ordered the gaskets yesterday, but your reply bolsters my confidence. I'll probably give it a go without removing it first just to see; got the set of three O2 sensor wrenches on loan from O'Reilly's.

PaulW

Gabor did mine at the transmission shop years ago, I stood and watched him. He used the big black crowsfoot one, I think it might be a harbor freight tool.