07 S6 - VERY rough cold start. BAD Misfires at idle and under load

A6 All/ S6 All
#44

Damn man, that is rough!

If I read the logs correctly, looks like you’re getting the following from the passenger side: 1, 3, and 4. And then from the driver’s side: 7, 8, 9, and 10. From my understanding the only cylinder that is related to your O2 codes (B2 S1, B2, S2) is cylinder #4 as it shares that bank of O2s with cylinder #5. You might be right in that some kind of harsh chemical caused the pre and post cat O2s to fail. One alternative idea I have is that they might share a common relay or wiring that is causing the heaters to malfunction. Does anyone know if there’s a common relay behind the knee panel below the steering wheel?

Also, I noticed you said a few of your IM bolts stripped (Ugh!) but you don’t notice any vacuum leaks when you smoke tested the system. Did you try smoke testing the system while hot after a normal drive?

Sorry if you’ve already done some of the above stuff… just trying to throw stuff at the wall in hopes that it helps cause I know I’d be ready to drive the car off a cliff if I was in your shoes!

#45

Yeah the last 2 months have been a wringer… haven’t been able to think straight with a death in the family, so troubleshooting has taken a back seat (I have a few other cars so this isn’t my daily)

B2 is driver side, so the misfires in cyl 7,8,9,10 follow those O2 sensors.

Also worth noting, Carbon clean was done in May. And the first batch of misfires occurred right after. Then later misfires occurred at varying times on varying cylinders. (1 and 7 misfires on Aug 18; 4 on july 15; 8 on june 16) I’m not sure if that how I should look at this that these were the times those cylinders were misfiring or if that was just the first time it happened (i’m sure justin can elaborate) Car ran great for a few months and I did have a few times where it ran sluggish… then one day in August (after the 18th) it just always ran sluggish.

As for the stripped bolts, the smoke test showed no leaks at the manifold, so for now I can state that there are no vacuum leaks that leak externally (I still feel like there is far too much vacuum coming from the oil cap, but I’ll deal with that oil/air separator issue another time) And did the smoke tests while hot as well as you had mentioned… I was getting more misfires while driving (see logs) and on decel so I figured it might be something happening while the engine was hot.

They also stripped while doing the final torque value, but still annoying because I want to pull the intake to do the injectors in the next few months.

TBH my plan this winter was to pull the engine, gut or remove the cats, replace 02s, replace injectors and paint the car. I do the work myself and have access to a lift in November so that’s likely when I will do the work. I did just want to share what was happening here so that in the case that someone else is in this predicament, there is a path and solution.

Not everyone is going to be thrilled or ok with yanking the engine, but it doesn’t really bother me.

#46

Sorry to hear about your loss! Family and friends first without a doubt!

Regarding the O2s, I was under the impression that the layout was like this (At least in North America):



                                     Back of car

       Passenger Side (ECU 1)    |           Driver's Side (ECU 2)
       O2 Bank 2     5                |             10     O2 Bank 4
       O2 Bank 2     4                |              9      O2 Bank 4
                                             |
       O2 Bank 1     3                |              8      O2 Bank 3
       O2 Bank 1     2                |              7      O2 Bank 3
       O2 Bank 1     1                |              6      O2 Bank 3

                                    Front of Car

Have I been looking at the layout all wrong this entire time? (I hope not!)

#47

Very helpful schematic…can we also include O2 p/n’s for each bank as well as the two collector O2s?

#48

Here you go: 8 total sensors.

https://i.imgur.com/kcMOaDC.png

B1 is Passenger Side; B2 is Driver’s Side (LHD) S1 is Front; S2 is Rear.

FRONT SENSORS (precat):

07L906262K - oxygen sensor
S6; Front (B1 S1); Cyl.#1, 2, 3

07L906262H - oxygen sensor
S6; Front; (B1 S1) Cyl.#4,5

07L906262J - oxygen sensor
S6; Front; (B2 S1) Cyl.#6,7,8

07L906262G - oxygen sensor
S6; Front; (B2 S1) Cyl.#9,10

REAR Sensors (after cats)

1K0998262S - oxygen sensor
S6; Rear (B1 S2); Cyl.#1,2,3

07L906265G - oxygen sensor
S6; Rear; (B1 S2); Cyl.#4,5

07L906265H - oxygen sensor
S6; Rear; (B2 S2); Cyl.#6,7,8

07L906265J - oxygen sensor
S6; Rear; (B2 S2) Cyl.#9,10

#49

Awesome! Thank you very much!

#50

Wow… very interesting. I was using this PDF from AW as my guide when coming up with the diagram I made up above. I noticed that it lists banks 1 thru 4.

My logic was that when you pull up measuring blocks 32 and 33 to look at the long term and short term fuel trims, VCDS displays


B1S1 Idle | B1S1 partial     ||  B2S1 Idle | B2S1 partial

B1S1 STFT | B1S1 voltage  || B2S1 STFT | B2S1 voltage

To make things more complicated we have 2 ECUs, and from the same PDF that you posted, the next page in that document lists which ECU collects data from which O2s. It looks like ECU1 collects output from the passenger side O2 sensors and then ECU2 collects output from the driver’s side O2 sensors.

So when you access ECU2, measuring blocks 32 and 33 essentially should look like:


B3S1 Idle | B3S1 partial     ||  B4S1 Idle | B4S1 partial

B3S1 STFT | B1S1 voltage  || B4S1 STFT | B2S1 voltage

Measuring block 36 on ECU1 will give you the O2 voltages for B1S2 and B2S2. Measuring block 36 on ECU2 should then display output from B3S2 and B4S2.

Sorry for the long-winded post. Just showing my thought process behind the above diagram. I want to make sure that I have this correct in my head, especially if I’m going to keep this car for many more years! Am I way off the mark here?

#51

My bad guys… fixing an error in my post above (doesn’t look like I have edit capabilities for my posts) The second “code” block should be as noted below:


B3S1 Idle | B3S1 partial     ||  B4S1 Idle | B4S1 partial

B3S1 STFT | B3S1 voltage  || B4S1 STFT | B4S1 voltage
#52

[quote=“murphenur,post:48,topic:8137”]

The data you listed here is wrong

#53

In your diagram you have two B1S1 sensors and that is obviously completly incorrect.

Here is how it works you have it correct here



                                     Back of car

       Passenger Side (ECU 1)    |           Driver's Side (ECU 2)
       O2 Bank 2     5                |             10     O2 Bank 4
       O2 Bank 2     4                |              9      O2 Bank 4
                                             |
       O2 Bank 1     3                |              8      O2 Bank 3
       O2 Bank 1     2                |              7      O2 Bank 3
       O2 Bank 1     1                |              6      O2 Bank 3

                                    Front of Car

The 02 sensors follow the pattern as you have listed here.

B1 = bank 1 S1= sensor 1 in that bank … Then you would have B1= bank 1 =S2 sensor 2 on that bank (post cat)
Since the V10 is broken into two banks per side you have two banks per side The other sensor on that same passenger side would be
B2 = same side of the motor as B1 but the second part of the system S1 = Senor 1 on the second bank

Then you have bank 2 of the total motor or the driver side of the motor. But so as to not confuse Audi techs Audi broke bank 2 or the driver side into new banks noted as B3 and B4

So on the driver side of the motor known as B2= bank two or driver side… Since the term B2 is already being use on the passenger side of the motor on ECU 1 Audi used B3 and B4

On the driver side you have
B3= bank 3 S1= sensor 1 in that bank… then you would have B3=bank 3 S2= sensor 2 on that bank
B4= bank 4 S1= sensor 1 in that bank … Then you would have B4=bank 4 S2= sensor 2 on that bank

So you have
Passenger side B1 and B2
Driver side B3 and B4
The primary 02 on each of these banks will be under S1 and the sensor post cat will be S2

Dont confuse the universal side refrence with the 02 refrence.
Audi calls the passenger side of the motor bank 1 and calls the driver side bank 2. This is for the over all motor but when you talk about the 02s its broken down into 4 banks.

Now to help make this even more confusing as you mentioned you have 2 ecus so the bank 1 ecu on older software versions flashed into the 5.2 motors broke the data into only two banks per ECU and not 4 banks total. So old documentation might still reflect this. But this was obviously hard to dignose so you will notice that all car fax data shows audi had a manditory ECU update to help make a change to 4 total banks other than B1 and B2 per ECU.

hope this helps.

#54 


                                     Back of car

       Passenger Side (ECU 1)    |           Driver's Side (ECU 2)
       O2 Bank 2     5                |             10     O2 Bank 4
       O2 Bank 2     4                |              9      O2 Bank 4
                                             |
       O2 Bank 1     3                |              8      O2 Bank 3
       O2 Bank 1     2                |              7      O2 Bank 3
       O2 Bank 1     1                |              6      O2 Bank 3

                                    Front of Car

MOTOR ONLY
B1 is Passenger Side;
B2 is Driver’s Side (LHD)

O2 SENSORs
Passenger side B1 and B2
Driver Side B3 and B4

S1 is Front; S2 is Rear.

FRONT SENSORS (precat):

07L906262K - oxygen sensor
S6; Front (B1 S1); Cyl.#1, 2, 3

07L906262H - oxygen sensor
S6; Front; (B2 S1) Cyl.#4,5

07L906262J - oxygen sensor
S6; Front; (B3 S1) Cyl.#6,7,8

07L906262G - oxygen sensor
S6; Front; (B4 S1) Cyl.#9,10

REAR Sensors (after cats)

1K0998262S - oxygen sensor
S6; Rear (B1 S2); Cyl.#1,2,3

07L906265G - oxygen sensor
S6; Rear; (B2 S2); Cyl.#4,5

07L906265H - oxygen sensor
S6; Rear; (B3 S2); Cyl.#6,7,8

07L906265J - oxygen sensor
S6; Rear; (B4 S2) Cyl.#9,10

Im not

#55

Awesome as always Justin! Thank you for clearing that up.

The part numbers are as quoted by the local Audi Dealer if anyone is wondering and also matches what “Genuine Audi Parts.com” has.

#56

Great work that is a lot of leg work.

#57

I’ve got a leak between the two throttle bodies and the intake plenum too. Did you end up replacing the intake plenum or did your fix resolve the problem?

#58

I had the same issue as you and Rally and used RTV on both throttle bodies and it worked perfectly. Just applied a thin bead on both the intake portion as well as the back side of the throttle body for added reassurance. Smoke tested with no leaks!

#59

Hey guys.

Quick update here.

Been a little bored so been trying different things.

Threw a trickle charger on the car. Got the battery fully charged and amazingly… no misfires. zero, nada, nothing. no flashing check engine light, car runs strong.

so I left the car for 4 days off the charger, did the same thing, started it up… and misfires back. car running rough and flashing MIL off throttle.

To finalize this, charged car until battery was 12.8V and tried it again. Sure enough, car does not misfire.

I have ordered a new battery, but does this make sense at all? I don’t have any low voltage DTC (except when the battery was dead) is this actually a thing that if the car doesn’t have a fully charge battery or the battery has a dead cell that it’s enough to cause a misfire?

I am still going through with gutting my cats and replacing the injectors over winter, but just thought this was such an odd troubleshoot.

any thoughts are welcomed.

#60

I think this is good news! For what it’s worth, I’ve seen this happen several times on my m6 that I don’t drive on a daily basis. I’ve resorted to using a trickle charger in between uses and I never see random misfires as a result anymore. I think our cars are so sensitive to low voltages that the ignition system goes nuts if it sees anything less than optimal output at anytime while the engine is running. I can only imagine how much joy you’ll have after putting the nail in the coffin on those misfire issues lol

#61

This does make sense. This is something that isn’t super common but this is a thing.

The ECU actually is the amp system for the coil packs and 02s. So if the battery is low the voltage amp output is low as well. You would think that when you start the car the alternator would put out a charge and fix all issues but its not the voltage output from the alternator but the actual battery voltage that dictates how things run. So if you have a low battery voltage you get reduced coil pack production output.

#62

Very interesting. I’ve ordered the battery so I will wait and post some updates and maybe see if it may have affected the o2 sensor (that’s really going out on a limb)

Still want to pull the cats, but if I can wait a few months that would be nice. Hoping that this will help some of the other guys on here.

#63

It should help the car overall. Not too sure about the 02s BUT they are heater code so maybe the low batt is effecting the warm up ability. But to be honest. I would think you would see more than just the one bank but… you never know.

Just be careful if the 02 completely faults out it can turn those cylinders off or put them into limp mode. It’s something good to keep an eye on.