Road Dawg

Hi there once again Forum Guru's. I have two codes P0175 & P0172 on my 2013 S8 75K. I have a ANCEL VD700 and ran several scans with cold startup live data.
My biggest concern is, there a loud distinctive chattering upon startup that slightly subsides when initial idle reduces! Oil quality is not great (due for change) Castrol 5w40
full synthetic always. Looking at the Live Data and the O2 sensors are fine! I hear the fuel pump primed without the engine started! Air filters are clean! Used a mechanics stethoscope
on the turbos and they are loud @ startup and quiet down after initial idle. Not sure what would stand out looking @ the data stream?? And yes, (( I did use the search bar before posting this time))
No specific parallel to my issue!! Thanks for any direction, The stealership hit me bad the last time. I am retired and fully mechanically inclined and appreciate some advise.

Thank You In Advance RD

MP4.2+6.0

I would try the most basic and easy first and see where you get:

1. Do an internal motor flush right before next change. I use Rislone when needed. Gunk has a similar product--the kind you add to oil, let idle 20 our 30 minutes, then immediately drain. It is against the theory the noise at cold might be hydraulic lifter noise ("sticky lifters" in old school speak).. Costs ten bucks or less incrementally to try.
2. A couple of Techron treatments in the gas--will clean fuel system and injectors, but not intake valves. I do a bottle every oil change in general.

After that I would:
1. Do the 75K tune up if you have not already--that is the 40K "major" cycle for the S8 that includes plugs.
2. Consider the old Seafoam spray into the engine--only DIY non-invasive way to at least try to clean the intake valves with direct injection. That would be on the theory your noise may be valves at cold, and maybe some running issues. BTDT on a Mini direct injection set up with heavy cold noise; that was the fix. Yeah, plenty of armchair posts around the web saying that's only for outboards, blah blah blah. Worked for me, and another ten bucks is way better to me cost wise than getting into mechanical head cleaning. But I would only go here after the prior ones if they have not resolved things to your satisfaction.

gk1

P0175 System Too Rich Bank 2 (Driver's)
P0172 System Too Rich Bank 1 (Passenger's)
– Check the Fuel Pressure Sensor -G247-
– Check the Fuel Pressure Sensor 2 -G624-
– Check the Fuel injectors - N30, N31, N32, N33, N83, N84, N85, N86-
(*You said you checked)– Check the Heated Oxygen Sensor (HO2S) -G39-
(*You said you checked)– Check the Oxygen Sensor (O2S) Behind Three Way Catalytic Converter (TWC) -G130-
– Check the evap system for possible contamination
– Check the Evaporative Emission (EVAP) Canister Purge Regulator Valve - N80-
– Check the intake system for leaks (false air)
– Check the vacuum lines for leaks

Road Dawg

Much Appreciated MP4.2+6.0 And gK1

I find myself needing to use the process of elimination along with "the most basic and easy first" !!!

My scan tool Data leaves me with more questions than answers. ( NOT GREAT @ READING THE NUMBERS)

Can a bad turbo(s) cause the two codes I'm getting? Also, will gasoline get dumped into the oil if either fail?
I'm tempted to pull the Turbos, to examine them first???

I picked up new Oil & Filter, Rislone/Gunk, and injector cleaner. The 75K service was done @ 71Kmiles!!!
I don't want to make anything worse, so if I set up the flush and oil change with the car running the way it is,
I'll need to leave it running for @ least 5-10 minutes. I'll stethoscope each injector to make sure they are all working, and
that should exhaust the fuel pressure sensor??

Thanks guys for your help and insight
RD

Road Dawg

(( UPDATE ))


Hey Guys. My instincts overcame me and I started tearing down tie top of my 2013 S8 75K. After YouTube and some AWESOME advice from you two, I found a couple things that shed some light to my problem!?!?!? (Pictures Attached)

Drivers side Turbo blades are bent, there's oil and the shaft has front to back play. Passengers side seems ok with a little front to back play! I haven't fully removed them to check/inspect the other side yet, I want to be prepared to finish the job
before tearing them out!!

Also, There was a split in the air-box/intake seal from assembly or previous removal, which could have been the culprit for the P0175 P0172 codes, or a combination of both???

Now I found two rationales for the screen filter underneath. Remove it all together, replace it with Audi' new screen upgrade, install a aftermarket external filter accessible on top for future cleaning???

Lastly, there's RS7 turbo upgrades everywhere.. any thoughts, insight, pro's and cons would be greatly appreciated??

Thanks in advance again RD

Side by side

Drivers

Passengers

Intake Seal Cut

gk1

That tear in the intake seal certainly would be a problem. Since that is on the pressurized side of the system I'm surprised you didn't get some sort of code for a boost leak.
The small amount of oil in the driver's side turbo is normal from the PCV. Obviously bent blades and excessive shaft play would not be normal. It's hard for me to see the bend in that pic and I also don't see housing contact to cause the bend. Could just be the photo.
No recommendation on what to do regarding the screen or which turbos to choose, it's a sort of search and make your own decision sort of thing.
Audi obviously feels their latest rev screen is adequate, but SRM and a few other owners feel it should be removed altogether. Just like some have had luck with the absolute cheapest Chinese turbos they can find, but personally not something I would want to try.
GL

Road Dawg

Thanks gK1... I didn't see nor can make the blades contact the inner housing!!! Most of the play is front to back, and I don't know how the blades got bent like that? I'll post better pics when I remove them! There's always one bolt that is in the worst place... lower passenger side. Radiator hose and air filter box both in the way, The filter box doesn't want to come up high enough to remove the bottom hose underneath

I'm leaning toward no screen, and monitoring and changing my oil more frequently. Done with Castrol... going back to Mobil1 0W 40 !!!
No Chinese turbos for me.. I'm thinking I can just replace the drivers side one? If I go with two, I'd likely upgrade to the RS7 Turbos. Good opportunity to clean the throttle body too.. thanks for sharing your thoughts.

Much Appreciated RD

MP4.2+6.0

Yes, seems like the torn rubber seal could explain things.

I suspect what you are seeing w/ the turbo fan blades is just factory shape. Maybe do some searches for other pics. If S8, same as RS7 and probably more of those around.

If you don't see any scraping on the housing, also not logical blades hit at all, and then not likely they bent unless something went down the intake passages. And then you would have bigger problems....

Lot's of Castrol's so you would need to be more specific. For Audi, it should at least be the Castrol Euro Formula ones, which are the only ones that meet the 502xx VW spec. That is, besides the dealer 502xx flavor that was Castrol too.

Find my post on oils and S8. I have moved to 504 spec, which is improved over 502xx for factors that matter. (referred to often as 504/507 if you see both) There is a Castrol which is 504 which I currently use. Mobil 1 0W40 is 502xx, but not 504. For obscure reasons having to do with a discontinued spec, it might get close, but that assumes no change in formulation in more than 10 years, which seems unlikely. It was my prior go to oil for my Audis out of warranty/AudiCare, but not with 504 now. If you want it in Mobil 1, it is Mobil 1 ESP 0W30 or 5W30 that meets 504 spec. Has to say ESP and be in those viscosities to be the 504/507 ones.

gk1

That's an interesting point MP4...
The S8 does not come exactly with RS7 turbos. And the pictures of those cast compressor wheels seem to jive with that.
S6/S7
079145722 right
079145721 left

S8
079145722A right
079145721A left

RS7
079145722B right
079145721B left

I know the OE RS7 units come with billet compressor wheels and a ceramic coating on the inner lip of the cover housing. I can't see the ceramic from your photos, but those certainly look like cast wheels. I was always curious about that and assumed the S8 had RS7 turbos, but it seems like perhaps they are RS7 sized, but still cast.

It is easy to see the difference between the cast gray S6/S7 turbo compressor wheel and the shiny billet RS7 wheel in these pics.
S6/S7


RS7

MP4.2+6.0

S6/S7 not really relevant to S8 or RS7, other than as an upgrade path starting from the lower performance 4.0T's. A8 4.0T +/- = S6/S7. But OP is starting from S8. S8 is fundamentally a different turbo set, as well as a different lower end and block. Not sure on impeller wheel specifics relative to RS7. But S8 is dual air box and RS7 is single and with different intake ducting. It could get into how the boxes/ducts and turbos connect up--and then some differences that yield different part #s for overall assembly.