Audi S8 D2 misfire Lambda sensor fault

[H24k]

My 1999 facelift 40v Audi S8 has a serious misfire which is very noticable at tick over and the car shakes quiet violently! Ive changed spark plugs, Coil packs, checked injectors etc etc and still the same however the car recently threw up some fault codes one of which is 16534 Check Oxygen (Lambda) Sensor Heating Bank 2 Sensor 1, found the info here http://wiki.ross-tech.com/wiki/index...ible_Solutions

Just wondered if anyone knows where this actual sensor is located so I can change it to see if its the cause of the misfire, my car is a UK right hand drive, Thanks

[The_Laird]

Surprised no-one has come along with a definite answer on this yet. I think these are before and after the catalytic converters, roughly below the handbrake IIRC

[richyb66]

Assuming it's similar to the 40v S6, the post at lambdas are below the handbrake but the pre-cat ones are in the exhaust downpipe close to the cylinder head.

The pre-cat lambdas aren't easy to get to in-situ, there might well be a special tool to get to them but I've not got it, the post cat ones are fairly easy to get to though. Personally, if I was swapping the pre-cat sensors, I'd drop the down pipe off the car.

This is how I did it on my S6, S8 should be broadly similar??

http://forum.a8parts.co.uk/showthread.php?t=4834

[mikes2]

I replaced the driver side pre-cat lambda on my 3.7 by removing the secondary air kombi valve which is directly above it

[H24k]

Thanks for the info guys, I was hoping the pre cat sensor was easy to get to so I can change it over myself, but with regards to dropping exhausts etc, thats something I cant do myself!! I was wondering if this could be the cause of a misfire, I mean would the lambda sensor cause this if its completely gone? Ive currently got my car listed on ebay but if I could diagnose the misfire then i would sort out the other problem which is the oil cooler and most likely keep the car instead of selling it as is cheap!!

Ive changed sparks, changed coil packs, done compression check on all cylinders checked injectors etc etc and kind of gave up!! lol

[The_Laird]

I'm not sure if that would cause a misfire (someone here will know and be along soon!).

But to get it changed, just find a decent independant local exhaust specialist and give them a call. Ask for a quote - I'm sure they could sort it in less than an hour.

[richyb66]

I'm not convinced that the lamba fault would cause a misfire either.

You say the misfire is noticeable at idle but are there any other symptoms when it's running normally? I had a "misfire" at idle and the car felt a bit down on power - no relevant codes were stored. After swapping a few bits and having a bit of a think, I finally tracked it down to a faulty fuel pump. The old pump was causing a fluctuation in fuel pressure that was causing the car to run poorly and it had seemed more noticeable at idle for some reason.

[Architex_mA8tey]

I was just going to say check the fuel system and pump! good call

[Goran]

As Mike says, front lambdas can be reached from above the engine by removing the Secondary air injection kombi valves (metal mushrooms on back of engine block). My local mechanic changed both of my front labmdas this way in less than 1 hour. No exhaust dropping necessary.

[ainarssems]

The fault code is for heating element of lambda sensor, very unlikely to cause misfires. The sensor in question is precat on the downpipe. Not sure about 40V but on 32V it's fairly accessible from the top if you have lambda sensor socket also there is not much space.

If you have VCDS check the measuring blocks for misfires to see if they are random or mostly on 1 cylinder or on 1 bank.