I’m back.....and misfires

A6 All/ S6 All
#1

Hi everyone-

I haven’t frequented these forums in awhile, but I bought my second s6 an 07 with 78k miles (98k miles now) a little over two or so years ago. Some of you all may recall the JHM promo video for breaking into the 12s. My car was the white one, it was at JHM for a lengthy stay, I actually had it shipped directly to JHM when I bought it to be part of the beta program. The car ran flawless for a little over a year (thanks jhm and count!) but the last few months have been tough.

I’ve had coldstart misfires and just misfires in general for the better part of the last 4-6 months.

So far I’ve performed the following:

  1. another carbon clean and pcv replaced
  2. replaced all the injectors (second set in <2 years)
  3. Swapped plugs and coils to rule that out.(coils and plugs were replaced during JHm visit about 2 years ago now)
  4. Checked compression and it was fine.
  5. Replaced the Intake manifold (thanks jhm for the latest one!)
  6. Replaced throttle body gasket

Tomorrow I am having them test the battery, clean the MAF, clean the airfilters, and replace the fuel filter. The low side fuel presssure was closer to 6 so thinking the fuel filter may be a bit clogged can’t recall when it was last done. Crossing fingers, but not entirely sold that will fix the issue. I’ve also read that the misfires could be caused by loose coil clips, when cold it creates a lean scenario and causes misfires. Once warmed up there is expansion and then no more misfires.

If that doesn’t fix it and after searching a few other threads I’m starting to think it could also be a bad 02 (I believe one was replaced by JHM already), possibly even bad cats, and/or the SAI. One thing of note I haven’t gotten better than 15 mpg since I got the car back from jhm but before I took it back to the shop it was hovering around 11 or 12, so thinking it is fuel related, but I guess it could be a bad O2 as well. Whatever it is it has to do with the startup routine, when I was still driving it, to get it to misfire less I had to turn it on then off then back on to get it a little smoother and out of the startup routine. The car has misfired so badly before that it has stalled out, this is after a few minutes of driving but not fully warmed up.

To be updated after I land…if the above doesn’t fix it I’ll have codes on Friday or so. It’s basically cold start misfiring on 5, 6, 7 and 8 from what I recall. Before the IM was replaced it was a hard misfire on cylinder 8 I believe. There is also a esp cel on for the yaw sensor, I’m told this is a different issue and not related but I suppose there could be a correlation of my issue is electrical.

Look fwd to resolving this soon with everyone’s help. Especially since my Audi vw mechanic is starting to scratch his head :-\ sorry for some of the rambling above I’m typing this before I take off in a plane.

————————
About the car
2007
Audi ibis White s6
98000 miles (cpo to 60,000 miles and no records between 60 and ~78k miles when I bought it)

Mods:
JHM ECU/TCU
JHM LW CP
K&N air filters
Magnaflow mufflers (I believe)
JHM front LW rotors (currently not installed, maybe for sale if anyone is interested)

Major Maint and repairs in last 20k miles:
10 flow matched injectors
New spark plugs and coilpacks
New intake manifold
Meyle XD Control arm kit
Front and rear Bilstein HD struts
Coolant expansion tank
Inner outer CV Boots
valve cover gaskets
Oil cooler O-rings
Resealed oil pan seal
Crank seal
New Radiator
Carbon clean (twice)
Cabin air filter
O2 primary Sensor B1
New battery (I’m in Arizona and heat isn’t friendly to these batteries, I also realized I never had the battery coded to the car so not sure if that might be causing an issue as well)

I think that’s the majority of it, I’m sure I’m missing a thing or two.

#2

Godspeed man. I feel your pain. S6 ownership is a labor of love and considering how deep we are into these cars, I guess necessity as well.

#3

here’s a few misfire ideas that come to mind:

-coil pack / spark plugs (I know, but it’s kinda the starting point). If you recently bought spark plugs from Amazon or where ever else, then consider that spark plugs may in fact be an issue. I hope you compared the gap on the old ones to the new ones.

-leaking valve cover (oil can foul plugs from leaks in circular seals on valve cover gasket). Oil might be pooling and seeping right above the hole for the spark plugs. Check it out and see how the plugs look. You said these gaskets were replaced, but it’s possible the new gasket install was botched from torque error or lack of silicone or whatever. Even replaced spark plugs will poop out in this situation.

-crap connection between coils and plugs. Consider pulling back the boot on each coil pack harness connector to see how the actual wires look that attach to the coil harness. Sometimes they fray. It’s a thing.

-ensure the bolts are there to hold your coil pack harnesses in place. If the clips are broken or damaged, then the bolts will help with a poor connection.

-vacuum leak. What a headache it is to investigate this one, and worth a second opinion if first mechanic says it’s ok.

-valve cover crack(s). Some Audi valve covers are actually made of plastic. My original valve covers were metal, and replacement (OEM) were plastic. Imagine that. Plastic ones crack. Metal ones corrode. You can’t win.

-low fuel pressure (pump? fuel pressure regulator?). Fuel filter is a good idea generally speaking, if you don’t know when it was done last, but I’m a little skeptical too that this will resolve the issue entirely. There is also a vent for your gas tank that closes when the car flips over (to prevent gas from dumping everywhere), which allows the fuel pump to empty the tank. Also the gas cap is vented to allow the fuel pump to empty the tank. Either way, low fuel pressure has it’s own set of more possible solutions if you eventually identify “low fuel pressure” as a problem.

-Parked for months? This could cause corroded fuel injector(s) if parked for months with “winter gas” in it (contains corrosive ethanol). Could also be water in fuel. Over time, fuel takes on water and loses octane (octane is basically misfire stability while fuel is under compression). Just an idea, since some people keep their S or RS off the streets during winter. I’m wondering why you are on a second set of injectors after just two years, unless it was just a move to rule out injectors as a source of misfire?

-check wires that go to the injector connector. It’s a thing for these wires to fray or break right off on Audi’s.

-engine ground. NOT the same as a battery ground. Could have been disturbed during previous work on the car.

-were there misfire problems BEFORE intake replaced? Or only since? Intake manifold gasket leak can cause misfire mayhem in one or more cylinders.

On a side note
-I doubt that your cats or SAI would cause misfires. SAI is basically an electric pump that just pumps air into your cats until they warm up, to help burn off emissions. That is wayyy downstream of any misfire situation.
-I have a 2008 S4, and battery coding was NOT necessary at the dealer, so you’re probably good with no battery coding on a 2007 S6.

I hope at least one of these ideas helps. Please let us know if you get to the bottom of it.

#4

FWIW I also had random misfires persist after injectors, plugs and coils and the fix was replacing and coding the battery. Batter going dead in about 5 days before coding on mine.

#5

Responses in line after each comment as vtgt

#6

Thanks, this is still on the list to investigate. Hopefully they will Test the battery tomorrow and we will see.

#7

Ouch––it feels like your S6 is a cancer survivor who just had a relapse. :frowning:

After finally getting my engine to run fine for the last year, I’m having thoughts of keeping it for a number of years (115K mi) as a second/ski car. That would make it easy to pour in the $$ for a new IM & JHM tune.

But now I’m not sure I want to jinx it…

#8

I’d say most problems on these are all known and all have fixes. Now we know that not all are the most cost effective, but that’s part of the risk and what makes it incredibly important to keep on top of maintenance. Spark plugs, injectors, carbon clean, coils, battery, HPFP, o2 sensors, etc. Just be mindful! The tune is incredible though! I’d highly recommend it.

On a side note, I do hate how our IMs are pieces of shit and there’s no after market. $1700 for a new revision IM is annoying to say the least.

#9

I wish I were independently wealthy enough to just decide “hey, I’m going to reverse engineer and cast my own IM”. one day maybe :smiley:

#10

I can tell you that the battery test may not reveal anything. One way to see if the battery is an issue is try boosting the car even if it turns it over no problem. If the misfires are reduced or gone, then I’d continue on with replacing that battery.

#11

Also reading eng92’s thread on his engine rebuild, I’m going to check the wiring harness for the coils and injectors and see what is going on there.

Just seems so odd that there is so much of an issue that seems to be voltage related. Could be battery, could be the power lead from the back the front, could be corrosion in the connectors, and associated wiring causing some resistance.

Just more food for thought.

#12

just to make sure this is correct. Are you just getting cold start warm up misfires… If you park the car in a garage is it better. Temp related… will you get the same issues on hot start…List of questions we will help sort this out.

#13

I’m curious about using a set of jumper cables to add a ground near the battery, just to add one that doesn’t go through the battery regulation.

I just have a theory that the regulation may be choking the voltage, ect to the ECU somehow.

#14

The shop is saying it’s just coldstart misfires now after the new IM. I can’t confirm 100% as I haven’t driven the car in 4 weeks+ however one time they stored the car in the shop which is about 80 degrees and when they started it in the morning it did not “coldstart” misfire. So yes, I think it’s temp related.

The shop was backed up so they just got around to installing the fuel filter today. So we are going to park outside and cold start tomorrow to see if there is any improvement. I’m being hopeful, but we will see.

#15

If the fuel filter doesn’t solve it and there are no other wiring issues from a fueling/injection standpoint I might try a new battery.

#16

Update: as advised by a few people I picked up the car to log some miles on it to see if any other fueling related codes or other codes came up. Imo the car is driving great once warm.

Right now it’s only throwing misfires on cylinder 5 (cel p0305) and 6 (didn’t quite get the code for this one). As I understand these are on different banks. They tried swapping spark plugs again and it was the same resulting cels.

In other news I also have a cel for abs controller, specifically I think the yaw sensor went out. Anyone know if that’s behind the mmi or under the rear bench? Or could this code be related to my misfires, perhaps a bad wiring harness?

The idle is rock solid, but I can still feel a little rumble. Other than that the car drives great after warmed up. One note the car was sitting outside today in 80 degree weather, and it still resulted in a check engine during warm up. So now I wouldn’t say it’s necessarily temperature dependent rather it seems to happen during the startup routine.

#17

Chances are your car is just more prone to cold start missfires. They all tend to do it but if its still present after the intake manifold change then I would say yes check for fuel trim issues as there is a good cnance that your getting a slight leak. might be from the PCV or might be from the intake manifold. Could be the manifold to the heads or the Y to the intake all of that can cause these issues.

If its good when its warm thats a good thing.

#18

Will keep my eye out for fuel trim issues.

We smoke tested the intake system (a few times) and there were no evident leaks. The PCV was replaced a couple months ago so doubt it leaking already.

#19

I had smoke tested my intake system years ago which did not reveal any issues. What ended up working was pressurizing the system (plumbed a pvc pipe to the intake) and then sprayed everything down with soapy water. That revealed a warped intake at the corners. Not sure why that worked and smoke test did not…

#20

Were you getting coldstart misfires because of that? I presume your taking about the air intake not the intake manifold?

In other news my mmi is going blank intermittently, I’m wondering if all of this could be a related to a loose connection/electrical issue. Stay tuned.