Misfires.... Battery Related A6/S6 Common Problem

A6 All/ S6 All
#1

Good morning all.

So, I’ve got my 2007 S6 that I’m waiting to pull the engine and do some work on related to misfires, ect. I plan on cutting out the cats, replace the 02 sensors, replace injectors, and other maintenance items.

One thing that happened last year is I had bad misfires that seemed to go away when I charged the battery fully. And would come back the minute I didn’t charge it or if I used another car to “boost” this car. Keep in mind the battery would show 12.2V or so, always had enough to spin the engine and it would start, run rough… after idling for a few minutes I could shut the car off and restart it, and boom. No misfires, car ran great.

I changed the original battery (yes from 2007) for an aftermarket AGM. H8 size, recoded the manual as per ross tech and other people’s post and still had the same issue.

So that’s when I assumed, it was the injectors leaking (as well as a ton of gas in the oil). Since I was going to be pulling the engine in the spring, I let this sleeping dog lie.

on to my 2007 Audi A6 3.2FSI purchase in December. Car uses same injectors, and had similar problems with misfires, leaking injectors, ect. Pretty much same issues as the S6 so applied what I knew.

  1. Changed Injectors
  2. New Coils
  3. New Battery (AGM)
  4. New FSI HPFP Fuel Pump (had codes for this); Fuel Filter
  5. New Fuel Pump in tank (failed)
  6. Carbon Clean
  7. New Thermostat, Coolant Temp Sensor and MAP Sensor (car is speed density)

So after changing the dead in tank fuel pump, car would turn over no problem, didn’t seem to get enough spark to start and would flood itself. So now, knowing that there were 6 brand new injectors, that should not be leaking, I am starting to get suspicious of battery. Changed out the plugs since they got soaked from the non start.

Check the battery, 12.5v at the terminals; 12.4v at the posts in the engine bay; 12.5v at terminal 30 as per vag com. Recoded as per ross tech… still no dice. Battery dips to 10.5v during cranking. Oh, and outside temps are -8C. Boggled by this, I hook up a running car to “boost” the A6. Now? Fires right up.

So, hook up charger to battery at 25amp and let it charge for a few hours. Took the car out a bit later, and started and ran fine. That is until later after attending a concert came out and car started, but was definitely misfiring. Dropped off a buddy and used his car to “boost” the car again, and not surprising… no misfires.

Got home and tossed on VagCom.

Got the following codes:

P0301 Misfire MIL ON
Cylinder 1

P1653 Please Check DTC Memory of ABS Controller

ABS Controller memory has this fault:

01314 - Engine Control Module
013 - Check DTC Memory - Intermittent
Fault Status: 01101101

Then some Freeze frame of some Hex Values.

So anyhow, I’m going to try getting a Lead Acid Battery to see if that makes a difference. I’m not sure that AGM batteries are holding up in our climate where I am. This morning was a brisk -32C.

But I see some common issues between the A6 and S6 as it relates to Battery and Misfires.

At one point I believe Justincredible had mentioned that the ECM takes the resting voltage of the battery to determine the spark output. I’m sure he’ll chime in.

I am just in disbelief that this is occurring in both cars. Same year. Same Battery.

What else can I check? I’ve checked and tested the grounds at the engine and battery, made sure battery terminals are cleaned. I tested the voltage at the battery and the front, next test is at the starter.

Also curious to test the resistance of the battery wire from the back to the front terminal. I’m contemplating using some jumper cables to go from the battery to that front post and see if that eliminates the issue.

I’m more than frustrated with both cars, but I’ve seen so many posts about misfires, the various problems and fixes that we are suggesting just to still have misfires.

Hope that this helps someone or if someone else who is experiences unexplained misfires can try “boosting” their car and see if they go away.

any comments or thoughts are welcome.

#2

Hello Murph,

I have an 07 A6 4.2 FSI (BVJ) and I experience the same issue currently, and have for the past year or so. I would say the same exact symptoms that you describe above. Within the last year I’ve replaced plugs, VCG’s , Coils, Fuel filter, and cleaned the maf. As well as looked everywhere for vacuum leaks, carbon clean performed within the last 15k miles.
I have found the same thing to be true though as far as boosting the battery. The car will not have a cel at times but I can feel it misfire. If I drive the car and shut it off after running misfires go away. Or the same will happen if I just boost the battery prior to running.
I have yet to replace my injectors, I do have a Misfire that continues to show on Cylinder #2. Just as you have one that shows up on Cylinder #1, I was thinking it was a bad injector. But I was going to replace this battery first to see if that fixed anything. The car definitely feels stronger and doesn’t misfire after a boost. I will check back in after I replace my battery and see if that changes anything. Hopefully we can trace down the cause of this issue

#3

Yes you are right. The battery is a huge part of how the car runs and some of the mail components run directly in line with available battery voltage. As a matter of fact the JHM calibrator (who is on this site) showed me several injector maps that work Via actuall battery voltage. There is a long list of things but that is one of them.

Also reading directly from other sorces that parts of the ECU only come on line If there is available battery voltage. Things like the ECU power the coil packs and injectors 02s etc. But that is dependent on battery voltage.

Now keep in mind you have voltage and AMPS. you can have a charged battery say 12.v but its not a constant and when you start the car you should never see your voltages fall that far EVER. That’s a week battery.

This is why cranking AMPS are a big deal. Also get a really good battery like a yellow or red top battery optima they have been a good fix for several people that have seen the same issues you have.

#4

Update.

Changed out AGM Battery for Regular, Lead Acid Battery. Recoded battery regulation module, and no more misfires.

12.6v at battery; 12.6v at front posts. Car runs like it should.

Odd enough, pulled out the AGM battery and it was showing 12.97v after being off a charger for more than 24 hrs and after starting the car a few times.

This morning I measured the battery again… now 13.43v. Makes little to no sense, but I’ll take it back to the shop I bought it from and get it tested.

I’m beside myself in terms of figuring out this battery issue… AGM battery drops to below 10.5v on cold starts, but still shows decent voltage and cranks car no problem. So much head scratching.

In any case, hope this helps someone else chase it down. I still want to do some logs on the battery regulation and wish I had more info on how it’s supposed to work.

I’ve measured voltage while running with the old AGM battery and it was at 13.7v at idle, rising to 14.4v at cruise. I’ll retry this again tonight.

#5

A friend of mine had same problem with his Cadillac CTS-V. Battery replacement fixed misfire, and the old battery seemed to start the car no problem.

#6

Subscribed as I’m chasing my own misfire issues as well. We think they are just cold start misfires at this point, so battery is still on my list to check.

#7

This misfire issues go away once the car is warmed up vtgt.

Seems to be a voltage issue, and this is not isolated to the V10s either. My S6 is similar to what you’ve done… same list, JHM tune, ect.

My next steps are a non agm battery in that car too, cut out cats and replace the O2 sensors, along with the injectors being replaced.

It’s definitely more pronounced on this 3.2L V6 than the V10, but I have a feeling that it’s mostly 2 cylinders that get all the misfires (1 and 6 on the V6) and on the V10 it seems to only be 2 cylinders as well, but more random in my case.

I just feel like there is something missing in this equation, and related to the battery management software. I’m more than annoyed that it’s a similar problem on two cars I own, but it’s kinda nice to be able to trouble shoot both as well.

I’m atleast 8 weeks away from working on the S6. So I won’t have any updates for a while.

The A6 3.2 however, has been running flawlessly since the battery change, altho the cranking before starting is way longer than I’d like it to be.

Worth noting that I switched up the spark plugs to nickel plugs by AC Delco. The A6 kept fouling the nice and expensive iridium plugs, and I don’t mind experimenting on that car, especially since changing the plugs is a 15min job. I feel like these cars run on the rich side, and the spark plugs are getting fouled early and could be related to the start up routine.

Anyways I’m continuing to work on this and will switch back to the iridium ones in a few weeks.

#8

I don’t know if you are aware, but you can monitor the misfires on each individual cylinder in real time using VCDS.

The measuring blocks are:
15-1,2,3 16-1,2,3 17-1,2,3 19-1

That is how I found I had a stuck injector a few years ago. All the counts were are at zero except for cyl 7 which the numbers were just a blur as the counter increased.

#9

eng92. I did know that you could, but never tried using it. I’ll use that next time.

#10

I notice that the battery regulation is done on the ground side of the battery… like the module is apart of the chassis ground between the battery.

I’ve got a crazy idea to add another ground at the trunk and see if that makes any changes.

#11

Did anything come of this?

I’m also getting random cold start or idle misfires that disappear while driving. The car runs great at speed. I keep forgetting to put the battery back on the CTek for a recondition cycle, but that seemed to fix the problem last time—for awhile at least.

Are occasional idle misfires just a nuisance—or do they lead to bigger problems down the road?