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

A6 All/ S6 All
#21

These things are horrible… I cannot believe Audi gets away with using such an inferior part on such an expensive engine. End rant.

This is actually a pretty simple job, but given the amount of space allotted it’s challenging in the sense that you’re basically taking out one screw completely blind.

There is a bracket I believe that goes from the intake to the oil separator that needs to be removed, both are t30 torx screws, if I recall correctly.

From there disconnect the breather hose from the side of the oil separator as well as the driver’s side valve cover. Just be careful not to damage it as overtime they get brittle and I think they are upwards of $200 to replace them.

From there you will need to use a t30 bit to get the top and bottom screws off of the oil separator. I prefer to use something like this in order to get them started. Once loosened it’s easier to just do them by hand. Be careful not to drop the bottom one! I wedge an old rag in between the firewall and the engine in order to (hopefully) catch it in the event that it falls.

Lastly there is the oil return line from the bottom of the separator that leads back to the top of the block. That will need to be removed from the old one and put on to the new one. Might as well use a new hose clamp while you’re at it.

Installing is essentially the reverse. Word of caution: do not overly force the new one in to the port! The oil separator adapter that links it to the lower intake manifold is only secured by ONE bolt and because it’s very soft it is easy to strip/break the mounting point and you will have to remove the entire intake in order to (hopefully) re-tap the fouled up screw hole. If you’re having trouble coaxing it in, use the smallest amount of silicone spray/sil-glyde to provide a little bit of lubrication. I say smallest amount possible because you really don’t want that getting sucked into a combustion chamber.

Hopefully this helps! Again, it’s a pretty straight forward job that just requires some patience and funky hand work in order to coax the bottom t30 screw out!

Keep us posted!

#22

Thanks for the writeup, man! You described it very well. The hardest part was finding tools that would fit in between the firewall and the part, and also accessing the lower bolt.

Unfortunately, did not solve my issues. Back to the drawing board…

#23

Check the suction jet pump. $27CAD part on my car that has caused so many issues for me.

Part number 078 133 753A (taken right from the part) Will be installing tonight.

I’ve had random misfires and unable to find any other leaks anywhere, but seems that the pump has failed and is bleeding off vacuum somehow.

You can test this if you pinch the hose leading up to it… if the car stops misfiring this could be the issue.

It’s located on the passenger side near the passenger side throttle body. Just follow the hose.

Google the part number and you’ll see the item.

I will report back tonight after I install mine, but wouldn’t be surprised if this is your issue.

#24

thanks for the tip…let me know how it goes

#25

Glad it made sense and you were able to follow it!

For what it’s worth I had a semi-leaking suction jet pump but did not have misfires associated with it. It’s a pretty cheap and easy part to swap out so it’s not the end of the world if it doesn’t correct the problem. Furthermore, I would suspect that a complete failure of the suction jet pump could potentially cause the car to lose breaking capabilities, so certainly worth the piece of mind.

#26

Replace suction jet pump and got rid of higher rpm stumble, but must have a leak somewhere near the intake plentum… deal with that tomorrow.

Just odd, and maybe very coincidental that it’s happening now.

I had done the carbon clean in May, changed plugs, coils, valve cover gaskets, added intake spacers and car ran like a champ.

2 month after that (last week) started misfiring. Same codes and random cylinder as OP.

I’ll check a few more things and report back… very frustrating. And likely avoiding the inevitable need for injectors… just seems weird for 4 or 5 cylinders to misfire over one weekend from having none.

#27

Damn, that is rough. When the carbon cleaning was done, did you have the [urlhttps://jhmotorsports.com/shop/catalog/vent-hose-crank-case-to-maf-hose-oem-for-s6-s8-52l-fsi-v10-p-3994.html?cPath=0_1]vent hose[/url] replaced that sits on top of the crank case? I lucked out and mine appeared to have been replaced fairly recently when I did my carbon cleaning/intake replacement/injectors, but I believe that is a common issue on our PCV systems and is virtually undetectable without the use of a smoke machine to determine whether or not it’s leaking.

#28

Murph can we get you to make a separate thread for this. If you can post a few easy locational pictures for people. Any time we can fight these misfire monsters and make positive changes it helps out everyone if we can document it. I’m working on a misfire master thread and it helps to have each part and conclusion listed if possible. since your suction pump helped it would be great to have a little info on that from you if you can.

Here is how you post pictures to the site.
http://audirevolution.net/image_uploader.php

#29

Hey Justincredible - I was thinking that too about starting a new thread, but this is related to the OP symptoms now. (I’ll post pics tonight, I know how to post pic, but it’s annoying to upload to imgur, ect and then post here again)

It appears that I also have excessive vacuum in the crankcase, oil cap is difficult to remove now that I’ve replaced the suction jet pump, and removal of oil cap causes serious stumble and stalling from the engine…

So I will replace the oil separator (even if it’s only 2 months old) and see if that helps.

I will do some logging too, I need to also check out O2 sensor readings and mass air sensor voltages to eliminate any other issues.

I will post an update when I get that done.

#30

Sweet! I would be interested to hear what your MAF readings are at WOT. I am only able to achieve around 155/160g/s at WOT from both MAFs on my s6, giving me a total of about 310 g/s at WOT.

My research leads me to believe that at WOT we should be seeing a combined total of around 350 g/s (170 - 175 per side) but I literally could not locate a basis for comparison so this would be interesting.

#31

I will try that tonight.

#32

ok keep us posted. I was just talking about seperatly sharing the changing of the suction jet so that has its own thread with results as an option. I don’t think we have talked about the suction jet much and a thread on just that would possibly be helpful. But yes please keep involved in this thread outside of that part.

#33

Update.

Still haven’t done logging (just haven’t had time)

But just looked at my codes and my misfires are on the following cylinders: 9,10 and 4,5. 6 comes up intermittently.

Seems that the cylinders that are misfiring share the same cats on each side… could be co-incidence, but could be clogged cats. Do we have anyone who’s had that issue yet?

#34

Ironically I’ve been having fuel trim issues with cylinders 4 and 5, granted no misfire issues. Knock on wood!

Given that you said you still suspect a vacuum leak somewhere, this could be something as simple as the rear most bolts have backed off letting unmetered air in. I’d check that first. Spray some starter fluid towards the back of the intake at the base to see if the idle changes.

From there I’d probably check out measuring blocks 36 from both ECUs to see what’s going on with the downstream o2 from each bank. At idle and at normal operating temp, you want to see a pretty steady reading of about .70/.75 volts from each rear o2. If you see the rear o2 voltage start to fluctuate between lean and rich at idle then it’s a good indication that the cat(s) are bad.

#35

Thanks. I’ll take a look at that.

Still can’t find any vacuum leaks… I’ve tried brake cleaner as well as starting fluid and no change in idle. Car was smoked tested this weekend too… nothing. I still don’t understand why there is so much vacuum in the valve covers. I’m thinking the “oil separator” may be broken (even if it’s only a few months old), so I ordered one anyhow.

#36

The info on spraying starting fluid is a great idea and I would spray it around the base and the back of the intake. If that shows nothing look further into spraying in or at the section connections of the intake where the top meets the bottom and where the Y pipe meets the intake.

You won’t likely hear the idle change so to get real info on whats going on look at block 001 that should be instant fuel correction. It should be in a percentage. Since you actually have 4 banks you need to know that bank 1 and 2 are on the passenger side and banks 3 and 4 are on the driver side. Lots of people get that confsed. When looking at the Vag log for the 5.2 it might just show up as block 1 and 2 on each ECU. let me know if that made sense.

#37

Ah, that reminds me Justin - while talking about the Y-pipe… another place that I noticed was the oil separator adapter that essentially feeds into the back of the lower intake. There is an o-ring in there that I found to be leaking when I replaced my intake. I opted to just use RTV to seal it and call it a day.

#38

Thanks for that info Justin! I will look at that in a few weeks when I resume troubleshooting.

That oil separator adapter oring caused me issues a few times… I was able to find a replacement oring for that connection.

I have two thoughts in my head to what my issues are (I’ve said them before)

  1. clogged cats - but need to check measuring blocks ect for that (but the exhaust sounds different too, like it’s being restricted)

  2. hole in diaphram in oil separator. I unplugged the separator from the valve covers and still have quite a bit of vacuum in the valve covers.

I wish I could dedicate time to this right now, but I have to get my other car (95 Mercedes E320 Wagon) ready for a roadtrip/show in Minneapolis (430 miles away) If there’s any other members going to Eurowerks let me know.

#39

keep us posted. I would caution you to be careful before you come to the condlusion that your cats are plugged while this is an issue on the 5.2 motors its a rare one and you generally see a cat code before there is any real restriction. So I again would urge you to be careful on thinking its a cat issue.

Crank case pressure is one thing but you want to see crank case vacuum. so again I would caution getting too concerned just yet with that. Obviously too much is a concern but you are suposed to have quite a bit of crank case vacuum thats what stops your car from leaking oil out every seal.

#40

It’s just how much vacuum it’s pulling. I’ll get a gauge on it and post numbers. Car stumbles and dies with oil cap off.