2008 S6 - O2 sensor or something else?

A6 All/ S6 All
#14

I realize that a new intake might indeed be what is needed to remedy this. Just the nature of the beast, I suppose.

Confirmed that the RTV I smothered in between the two mating surfaces does indeed work. I sprayed it down with some brake cleaner at idle and it didn’t increase/decrease RPMs. Showing some promise there. If this works I will take it apart again and put a thin bead of RTV on both sides of the gasket so it doesn’t look like complete crap.

I did have a lean code that was stored in the ECU but did not produce a CEL. Though I’m not sure if it was before or after the application of RTV. I should have broke out my laptop and pulled the freeze frame data but was lazy and used my cheapo Bluetooth scanner to pull it. I’ve cleared it and will see if it returns during the next few drive cycles.

#15

Drove about 75/80 miles and checked for any pending codes and didn’t get any - this is good news!

My theory is that yes, carbon cleaning was done on the car prior to me taking ownership of it this past June @ 100k miles, but the down side is they weren’t really careful in reassembling the intake.

I will continue to keep an eye on any pending codes/CELs, but hoping this was indeed the issue. I will wait another several hundred miles before taking off the throttle body again and doing a proper application of RTV so it doesn’t look terrible in the engine bay.

Once the weather gets nicer in the spring I will still take off the intake to verify my thought process around carbon cleaning. I’m one of the lucky few that get to work from home so it’s not a HUGE deal as I will only put on maybe 1k miles between now and then.

Thanks for all the input thus far - much appreciated. If anything pops up I will be sure to keep this thread updated this way we have a record for future people who may possibly run in to the same issues as me.

#16

Its nice to hear the RTV might have fixed the leaking issue for now.

When it comes time to do the clean or more work let us know. If we can help we are happy to

#17

Sorry to bring up an old thread, guys… But I figured this is the best course of action in case there’s someone else out there with a similar problem as mine they can see everything documented in one thread.

I’m pretty sure you hit the nail on the head, SIX6SIX.

So I bit the bullet and pulled the intake off to do the carbon cleaning that every one of us S6 guys has to do at one point or another. Sure enough I found a piece of the intake wedged into one of the intake ports. I went ahead and ordered a new intake (Ugh!) from JHM (I did not opt for the intake spaces this time due to cost restraints) and installed it last night after work.

So far so good. Car seems to idle fine and doesn’t appear to have the sluggish idle after the SAI pump turns off after a cold start.

I still have a few odds and ends to do on it tonight as I ran out of daylight. I will report back my findings afterwards and will be sure to update this again after I’ve gone through several hundred miles to see if the CEL comes back.

Just super excited to get this out of the way… been a long time coming! ;D

#18

Glad to hear everything worked out great. Hopefully nothing but happy motoring from here on. The intake spacers, not mandatory, but good if you ever do track time or do a lot of sports mode driving in warm weather. Outside of that, hope all is great for many thousands of miles to come.

#19

So unfortunately there are still some kinks to iron out. I am still getting 2 codes:

The above was taken from ECU1. There were no codes stored in ECU2. I believe there was another thread where Justin covered how different ECUs monitor different banks of O2 sensors since our cars essentially have 8 sensors, or 4 banks. Just to be clear, can anyone chime in on the above? Is my car throwing codes for the passenger side (I’m in the US) bank of cylinders since this was pulled off of ECU1?

Where do you guys suggest I go from here?

Is this the hallmark sign of injectors sticking open/closed? Could one of the high pressure fuel pumps be on their way out? Some kind of crazy hard to find vacuum leak?

Really kind of stumped on this one… any help would be appreciated at this point guys!

#20

…Always seem to post again like 10 minutes after my update.

Re-reading the above replies the common theme are injectors. Is there any way in vagcom to verify for certain that the injectors are on their way out? When I had the intake out I could clearly see that the previous person who was in there before me left a bunch of the blue o-rings in there from when they swapped/serviced the injectors. I bought the car with about 95k miles on it and she has about 105k now. I held off on getting injectors from JHM because of the evidence I saw when I had everything taken apart. I assumed the previous owner had the injectors changed around 60/70k miles and thought there was no way they could have gone bad already between now and then.

I have a funny feeling I will be taking the intake off again soon. That’s what I get for trying to save another $600-ish.

#21

All the stuff you posted sounded like my situation. I put brand new injectors in at 91k and it’s been smooth sailing since then (now have 103k). Prior to that it was constantly chasing my tail. I did discover a few issues here and there that needed fixing, but ultimately the injectors were the root cause for me. Seems like that is the case for others too.

I am actually thinking about changing all the injectors at carbon cleans 50k apart just to deal with this issue proactively going forward. I have the old injectors that I pulled. Maybe I’ll send those out to JHM for cleaning and swap them in at 130k or so when I plan to do the next carbon clean.

#22

Its a hard call. You can look at the LTFT but the car is giving a rich code and then a lean code. So that is hard to get to the bottom of. Regardless of what the situation is injectors are a major thing you really want to make sure you know 100% are good. Your in a tough spot not knowing if they are good or not.

You got the code for lean and rich on the same day so its hard to tell. You almost want to clear the code and see how long before it comes back.

#23

I bit the bullet and ordered injectors from JHM. $600 after the core charge isn’t the worst thing in the world. Plus it’s obvious that this is just one of those things that literally HAS TO BE DONE to every C6 S6 on the road. Stupid me for thinking the previous owner actually replaced them.

Justin - as a side note, I did drive around last night with VCDS in hopes of seeing anything out of the ordinary. I did notice at one point the short term fuel trim (ECU 2, group 33, I believe)did jump up to about 25%. I did not think of viewing the long term fuel trim. Also, I did not see consistent misses on any of the cylinders. I think #5 had 2 misses during the 10 or 12 mile run that I did. The misses did not correspond to the lean condition, BTW.

The CEL seems to come back on after 10/20 miles after clearing it.

#24

[quote=“Nebuchadnezzar,post:23,topic:8810”]
And lean is what you’d think if it was bad injectors.
Yeesh. These cars can be frustrating at times.

#25

Ok from what you mentioned thats a VERYVERY big deal that means that your car is maxing out the additve for fuel support.

when it comes to the injectors from JHM its worth the money 100x over. I have been really looking into a S6 and I have been working with a lot of FSI guys over the past 6 years and injectors are the quickest way to wad up a motor and the other injector cleaner service is a half ass way of cleaning injectors.

A quick example. There was a big hp Golf R car that was running a stage 3 turbo kit his motor blew but it was just one cylinder that was damaged. He thought it was a bad injector that did the damage. So he sent his injectors out to the typical injector cleaning service only to have them tell him the injectors were fine. Thinking that the injector was still the case even tho the first typical test said it was fine the typical test only tests at 5bar MAX thats 70psi thats what the car idles at. JHM tests the injectors at over 1400psi… needless to say when the guy with the golf R sent his injectors to JHM… JHM found the bad injector told the customer. The cusomer had numbered the injectors and the number of injector JHM found to be bad was the same cylinder that was bad on his motor.

Moral of the story. you can save a few dollars getting cheap injector testing and cleaning but whats the point on saving a few dollars when it costs over 10 thousand dollars for a new motor. knowiing what I know now and knowing that the standard injector cleaning service tests and flows injectors at 70psi and JHM cleans flows and tests them at 1400psi to me it would be foolish to get your FSI injectors cleaned with the standard service. 70 psi clearly isnt enough

#26

Yea, in hindsight I should have just done the injectors when I had the intake off. Like you said… the cost isn’t necessarily that bad given you send your old ones back and get the core charge back, and the risk for prolonged operation with bad injectors can be well into the thousands.

I got the shipping confirmation from JHM today and they should get here on Thursday. Looks like I’ll break it all down on Friday night after work and then put everything back together on Saturday and cross my fingers.

Ironically I scheduled my car for its annual safety and emissions testing this Wednesday. I thought I had a good chance of fixing this issue for good with the intake but I guess not! I might have to see if I can “sneak” her through emissions testing by clearing the CEL and making sure all monitors are set and PRAY that it doesn’t shit the bed between it being parked and them bringing it in and scanning it.

Thanks everyone thus far on your input through this repair. I’ll be sure to keep this updated as I make progress.

#27

So today I installed the new injectors from JHM and got everything put back together and still have the same code as referenced earlier in this thread (p2089 too lean, bank 2) after driving for about 15 miles.

While in for PA state inspection, I had the shop do a smoke test and they found two leaks which I addressed (One at the oil separator and the other at the suction jet pump for the brake system). Why I couldn’t find them with starter fluid is beyond me when I sprayed everything down a few weeks ago.

I realize this doesn’t mean that there are no additional vacuum leaks present since typically only the more prominent ones are spotted and then it’s just a process of elimination afterwards as you track down the smaller ones. I decided to buy a cheapo smoke machine on eBay for like 75 dollars. I’ll hook this up to my compressor and see if anything pops up later on in the week and report back.

In the interim, does anyone else have any suggestions? I am leaning towards swapping the MAFs around and seeing if the lean/rich issues follow the sensor. Could one of the high pressure fuel pumps be going bad?

As a side note, I will say that I do notice the car has picked up some more power, most noticeable at the top end so the injectors weren’t by any means a waste of time and money.

#28

I tested my original manifold (it was the updated version) and found that it was leaking at the seams at the corners.
Mechanic pressurized it at low pressure and put soapy solution around the perimeter. It bubbled up quite a bit. I’ve got a video of it saved somewhere. We replaced the manifold, which was unfortunate because it appeared ok otherwise. But, in my case we ultimately replaced the injectors to eliminate the codes.

#29

No matter how you slice it. the JHM injectors are a good idea. I have heard of a few guys that say they can feel a stronger upper rpm with the injector cleaning.

Tracking down the vac leak is a big hill in some cases but with the injectors I would wait to see if you get a new code for the car being lean.

#30

Man, I’d be PISSED if my new intake was leaking like you described!

Cleared the lean code and it came back within another 15/20 miles or so.

So I smoke tested the intake/crank case both cold and hot and came up with nothing. I will say, if you have a compressor buying a pre-made paint can smoke tester from eBay is a pretty good investment. (I know, I know… you can make them yourself for like 20/25 dollars but I was feeling lazy!)

Upon further inspection I noticed on cylinder 5 the coil pack connector is missing its tab. Has anyone had experience of one of these backing off a little intermittently and causing issues? Could my issue very well be due to a coil pack connector backing off, causing a cylinder to essentially misfire which in turn makes the o2 sensor detect a lean condition and then the fuel system tries to compensate by adding more fuel in and then it starts firing correctly again causing it to run rich briefly?

#31

If the connector is not making a good connection you generally get a different code. So its possible but I would think that might not be a big issue. If you can obviously make sure you do what you can to get the connection to the coil pack secure

#32

Good point on it throwing a different code if that was the case. It’s probably not an issue because of the fact that the loom for the wiring is so stiff it will hold it in place. In theory!

I’ve been driving around with VCDS for the last day or two and logging output from bank 2 (where all my issues are coming from). I noticed that after I got a p2098 code (bank 2, post cat o2 sensor too lean) the bank 2 long term fuel trim at idle and long term fuel trim partial values BOTH went to 0% and they are stuck there! Meanwhile the short term fuel fuel trim for bank 2 continues to fluctuate, but is biased towards rich.

Anyone got any ideas?

If the pre-cat o2 reads rich and the post cat o2 reads lean, could this be as simple as someone previously servicing this car have reversed the wires?

#33

http://zenacad.com/chris/media/o2graph.jpg

Logged rear o2 data from banks 1 and 2 in vagcom, viewed in excel and made this graph to better visualize the data.

Blue line is bank 1, sensor 2 (good - no known issues). Orange line is bank 2, sensor 2 (bank that gives problems). Red arrow points out where bank 2, sensor 2 is slow to respond.

Looks like the initial diagnosis of a bad o2 was correct.