I’m back.....and misfires

A6 All/ S6 All
#21

Correction: the car is not running great even warm. I can still feel a light misfire or miss or slight rumble at idle that I didn’t feel when I first got the car or my previous s6… However idle itself looks almost ideal by looking at it. Much better now that the new IM is installed. My cold start setup is extremely rough but the check engine light no longer blinks.

While driving and below 2800 rpm the car seems to stumble a bit and really feels like it’s down two or three cylinders. It feels pretty terrible in like 3rd or 4th gear under load at like 1-2500 rpm it really kinda struggles and to me is feels like it even misfires in those rpms. I’ve kept my foot steady and I’ve seen the revs kinda bounce around in the low rpm if that makes sense.

However, Above 3k rpm almost feels normal and probably would seem that way to someone who hasn’t driven a super healthy tuned s6, but still not as fast as it was when I received it so I still think something is up.

There was a thought that the new intake manifold was stuck in the higher rpm setting and I still need to rule that out, but I don’t think that would cause all my misfire issues on cylinder 5 and 6.

I guess I am going to mechanic number 2 soon. My game plan is to have them check the items pointed out by boatmobile and others, that haven’t already been ruled out. Worst case scenario I’ll need to make a drive up to JHM. I know it’s a long shot but anyone in it near Arizona that knows a good shop. The shop JHM recommended goodapeed refused to work on my car, I thought that was weak given the types of cars I see them service.

#22

I think a lot of shops are probably realizing that the S6 or the 5.2 motor isn’t an easy nut to crack. Because of this it makes sense that some shops would want to stay away its out of there league.

If misfires are down to two cylinders. There are a few good things to check. Check compression on those cylinders. Then move both the plugs and injectors to dufferent cylinders. This isn’t super easy but its going to start telling you more and more.

#23

Compression was checked on all cylinders after the intake manifold was replaced and it was noted that it was fine.
I believe the plugs and injectors we’re swapped to different cylinders and it still misfired on 5 and 6.

#24

Have you checked channel 93 cam/crank relation and short term fuel trims? Do they look normal?
I mean, typically if there is a problem with phasing all cylinders would misfire not just 5/6 but…just double check.

#25

I just randomly decided to check these forums finding your thread. Very interesting as my car is fucked right now as well with similar symptoms. I have an 2008 S5 which I replaced the battery with some O’Reily battery in Sept '18 ignorant to the need to program/discharge the battery to the car.

I have had intermittent MMI power surges, especially under full throttle, happened about 5 times since I installed the battery. However, right now my car feels as if its in full limp mode with anything beyond 1/4 throttle depression. Shop discovered HPFPs are not functioning electronically (they can manually turn them on, test them through VCDS, and they make pressure upon ignition, but after that nothing). Also at the same time pumps failed, my right front head light ballast was fried. We have replaced HPFPs, high pressure sensor, discharged and programmed battery, checked SAI, checked fuel for water, checked gas lines for pinches/kinks, checked wire harnesses, LPFPs…everything. We are not at replacing the ECM reprogramming it, and then reflashing the APR tune.

Been in the shop for 5 weeks now…I may ask them to do the battery to OEM next ???

#26

Replaced my aftermarket battery for a new OEM and I still have same problem. Onto the the ECM now

#27

The battery is a issue for lots of people and to be honest its something to make sure your on top of but in the case where the cars have more than one code espically for fueling you want to go down the path of checking LTFT and all other areas.

#28

I’m going to order a vagcom and go from there, I know I know I should already have one. What areas should I check once I get it in?

#29

Well just to get everyone up to speed. Car is still misfiring, I’m on my second mechanic now, his son also owns a s6 and he has worked on it so maybe that will help.

However, I met a Land Rover service advisor last night and we were talking. I seemed to have developed an intermittent exhaust sounding rattle on the left side, not all the time but occasionally maybe once a week or less. He seems to think that one of the cats ceramics is damaged which is causing me to have such a shitty startup routine. He has an Audi/VW tech that’s working for him now so he says to bring him to diagnose for free, and he has some expert exhaust folks that can fix if need be. I told him it’s an engine drop to replace the cats and he acknowledged that so we will see. So it seems i have my third option now.

#30

Hopefully it’s not cats. Dropped my car off this morning and forgot all about mentioning my cold start misfires lol. Probably won’t get the car back today anyway, but pray for us S6ers

#31

Headed to third shop tomorrow, wish me luck!

#32

oh man… This is a great example of just how special these cars are and how few really know about them.

Are you getting any codes or stored codes. Usually the cats are something you get a code for. What are your fuel trims? Check fuel trims they are a good first line is helping tell you if you have a leak or not.

Next time you start your car pull off the plugs from the MAF sensors. If the car starts up better and isn’t having misfires as bad that would tell you something as well.

#33

Missed this post. Will check those items out. I had a hunch it might be MAF related awhile ago. This seems like an endless witch hunt…they ruled the cats out somehow and said the rattle I heard was the exhaust hitting up against something so I guesss that’s goods news.

So far the third shop has said that the previous shop has been pretty careless with their work . Their diagnosis so far is:

  1. Bad Vac leak under intake manifold and potentially elsewhere including gaskets to the IM itself.
  2. The throttle body gasket that the previous shop replaced is leaking as they think it’s the wrong gasket
  3. They claim the air intake tube to the throttle body is warped causing turbulence as well.
  4. They claim both banks are running rich which is interesting because you would think if you had a vac leak you would be running lean. Not sure if that’s actually triggering a code, or they are just looking at fueling. If only looking at fuel trims that could be misleading cause the tune could be causing me to run rich.

I spoke with Jimmy and we don’t honestly think that these leaks would be causing these amount of misfires, but I guess it may be possible. I have misfire on 1-4-6-7-9

That’s all I know so far, this is an Audi tech at a Land Rover dealership but he has all his equipment. I know the SA and they are diagnosing for free, hope to know more Monday.

#34

Well that would be good news if all of this is due to bad gaskets and vac leaks. Those things sound like they are relatively cheap to fix I guess. Maybe the car is just trying to catch up with the leaks to balance things out and leading to misfires.

#35

Hi!

I’m new to this forum and to the S6es.
I bought my first S6 in mid May, this is my third Audi so I know my way around them.

When we picked up our S6 it has a couple of fault codes.
Misfire on a couple of cylinders, system to lean on both banks and so on.
When it was idle I removed the dual hose “box” going in to the PCV, the already rough idle became more rough.
When I then blocked the hole to the PCV with my hand, the rough idle completely stopped! I could place a cup of coffee on the intake manifold, with no spill. It was totally stable and a completely different engine!

So I did, as I’ve done on our previous A3, a PCV delete. The valve breather that was going in to the PCV is now breathing freely to the atmosphere through a 22mm hose in each side.
Our A3 did 160.000 km with such a set up (total 335.000km) and the S6 has done 2.000km now with this setup.
Still no misfires and no faults whatsoever. Engine is still rock solid on idle and it is as new!

My suggestion is to give this a try. No tools required!
Just pop the The dual pipe going in to the PCV and block the PCV with your hand. Be aware of the strong vacuum!

#36

Can you post a pic?

#37

Do you do much sitting in traffic with the windows open? I would think you would smell burnt oil in the cabin.

#38

My pcv was replaced a few months ago.

#39

Sure.
Remove the red circle and block with your hand at the green arrow.

https://d2aztkdj0ezvrk.cloudfront.net/items/3C3r1C2E0z3O45281T09/Skærmbillede%202019-06-23%20kl.%2009.16.46.png

No, windows is normally closed, I normally just use the sunroof.
But I did try yesterday and I didn’t notice any smells. My A3 was a TDI and the smells there was horrible.

Then it might not be the PCV, but it wouldn’t hurt to try it out.
Just block the end pipe at the green arrow with your hand and get someone else to start the car see if it makes a difference. Wouldn’t hurt.

#40

That is the oil separator and the PCV unit. Its a terrible idea to just leave it open. Its the PCV that system keeps the crank case pressure down and helps keep carbon more at bay.

The idea on opening the PCV system for testing just to try is a great idea. To actually have that as a long term solution is a bit absent minded.

On some cars without the oil separator maybe its not as impactful but since the V10 has a long history of blowing out gaskets venting to atmosphere wouldn’t be the greatest idea. Also remember that on the closed ring gaps you need to have vac pulled out to keep the rings sealed. So for multiple reasons it would be a terrible idea to not have the system hooked up.

Lastly if you know that unhooking and blocking off the oil separator and PCV unit stops any misfires why wouldn’t you just replace the unit. In theory you basically just proved its bad.

Kimovitzh welcome to the forum. Thanks for the post and suggestion… Maybe try seeing how much oil of any comes out of the PCV tubes since they’re not hooked into anything… Also keep us posted many in the past that had issues with holes in their PCV units or hose ended up getting fuel trim codes. It would be interesting to find out what and why.