Weak battery causing misfires?

[Tkalxx]

Just got cold here (-15C) and had a CEL pop up a day after our cold snap. I scanned the codes, getting random intermittent misfires on both engine banks (no additional codes). Spark plugs and coil packs were replaced ~35,000km ago and a CC done in between then and now. Voltage is below 13.7V on a few of the misfires which is sparking my question; pun intended. I know when the cold comes, weak batteries tend to expose themselves and I don't know the last time the battery was replaced (at very minimum 6-7 years ago). I know I should check the battery and alternator voltage but don't have access to a multimeter at the moment. Any thoughts?
__________________________________________________ ________________________
Address 11: Engine II Labels:. 079-910-560-BNS2.lbl
Part No SW: 8E1 910 560 J HW: 8E1 907 560
Component: 4.2L V8/4V FSI ª0010
Revision: 57H15--- Serial number: XXXXXXXXXXXXXX
Coding: 01040009180F0160
Shop #: WSC 22103 444 53784
VCID: 2D07094D111CC92F521-8078

5 Faults Found:
000768 - Random/Multiple Cylinder Misfire Detected
P0300 - 008 - - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 2
Reset counter: 255
Mileage: 118738 km
Time Indication: 0

Freeze Frame:
RPM: 1433 /min
Load: 58.0 %
Speed: 0.0 km/h
Temperature: 27.0°C
Temperature: 12.0°C
Absolute Pres.: 930.0 mbar
Voltage: 13.208 V

000772 - Cylinder 4
P0304 - 008 - Misfire Detected - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 118738 km
Time Indication: 0

Freeze Frame:
RPM: 1433 /min
Load: 58.0 %
Speed: 0.0 km/h
Temperature: 27.0°C
Temperature: 12.0°C
Absolute Pres.: 930.0 mbar
Voltage: 13.208 V

000774 - Cylinder 6
P0306 - 008 - Misfire Detected - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 119150 km
Time Indication: 0

Freeze Frame:
RPM: 1091 /min
Load: 70.2 %
Speed: 14.0 km/h
Temperature: 48.0°C
Temperature: 26.0°C
Absolute Pres.: 950.0 mbar
Voltage: 13.716 V

000771 - Cylinder 3
P0303 - 008 - Misfire Detected - MIL ON
Freeze Frame:
Fault Status: 11101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 119150 km
Time Indication: 0

Freeze Frame:
RPM: 1091 /min
Load: 70.2 %
Speed: 14.0 km/h
Temperature: 48.0°C
Temperature: 26.0°C
Absolute Pres.: 950.0 mbar
Voltage: 13.716 V

000776 - Cylinder 8
P0308 - 008 - Misfire Detected
Freeze Frame:
Fault Status: 01101000
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 119216 km
Time Indication: 0

Freeze Frame:
RPM: 1082 /min
Load: 54.1 %
Speed: 14.0 km/h
Temperature: 69.0°C
Temperature: 32.0°C
Absolute Pres.: 940.0 mbar
Voltage: 13.589 V

[Tkalxx]

Just had a second thought about this and it's very stupid to think this is battery/alternator related. Any guidance is appreciated.

[Pyromatic177]

I think it’s just the car being temperamental tbh. I get the same thing on my 08 and the PO had it at the shop so many times with no answer as to why it does. Just random and goes away

[Kenny147]

Two things...the cold can do some “odd” things to the electrical system and even though RS4’s are still fairly analogue, don’t discount the effects of a really cold spell. Secondly, when the battery gets past its optimum, it can cause all kinds of similarly odd issues.

I wouldn’t worry too much and rescan after it warms up a bit.

[Pyromatic177]

Two things...the cold can do some “odd” things to the electrical system and even though RS4’s are still fairly analogue, don’t discount the effects of a really cold spell. Secondly, when the battery gets past its optimum, it can cause all kinds of similarly odd issues.

I wouldn’t worry too much and rescan after it warms up a bit.

And also to add. While the car can have some odd behavior IF there was an issue these cars have a pretty good way of telling you via fault codes. Unless, like me, there was a ecu problem and it caused it to show random codes lol

[Tkalxx]

And also to add. While the car can have some odd behavior IF there was an issue these cars have a pretty good way of telling you via fault codes.

It's strange this came with no other codes.
I was doing some reading and I also tested the fuel trims initially thinking it was a fuel/injector problem. Please excuse my knowledge level of vcds, but from my understanding the fuel trims are how much the ecu is adjusting fuel in order to hit the target base map A/F ratios. (i.e. a vacuum leak would cause the car to lean out at idle since it's not getting enough air) From what I've heard, anywhere +/-5% is healthy so I don't think that's a concern for me. Correct me if i'm wrong.

[Pyromatic177]

It's strange this came with no other codes.
I was doing some reading and I also tested the fuel trims initially thinking it was a fuel/injector problem. Please excuse my knowledge level of vcds, but from my understanding the fuel trims are how much the ecu is adjusting fuel in order to hit the target base map A/F ratios. (i.e. a vacuum leak would cause the car to lean out at idle since it's not getting enough air) From what I've heard, anywhere +/-5% is healthy so I don't think that's a concern for me. Correct me if i'm wrong.

This is also out of my current knowledge base. Hopefully someone can chime in!

[Kenny147]

I've had a single misfire event since I've had the car. I'd cleared some old codes and on startup, it went a bit nuts for a couple of seconds, so I switched it off. Read just the misfire codes, cleared them and all was good. I know its a bit different from your situation but it just goes to show you can just get a misfire code on its own, which just goes away.

[Tkalxx]

I've had a single misfire event since I've had the car. I'd cleared some old codes and on startup, it went a bit nuts for a couple of seconds, so I switched it off. Read just the misfire codes, cleared them and all was good. I know its a bit different from your situation but it just goes to show you can just get a misfire code on its own, which just goes away.

I'll clear them and see what happens from there

[jsyn828]

Around 2013, I had some weird fault codes, some misfirings, due to a bad battery and the cold temps, along with some carbon build-up. New battery and cold weather, the issues cleared. The beginning of this year, had a couple misfires, the battery was going again. Replaced it, and all is good again FWIW

[Tkalxx]

Around 2013, I had some weird fault codes, some misfirings, due to a bad battery and the cold temps, along with some carbon build-up. New battery and cold weather, the issues cleared. The beginning of this year, had a couple misfires, the battery was going again. Replaced it, and all is good again FWIW

Battery was on it's way out... Fully charged potential was 12V. Replaced with a new one and no more misfires since.

[sandros1]

Hey Tkalxx

What battery did you go with? I've moved from east coast to Normal about a year ago and my options for sourcing a battery are minimal in my area. Thanks for any info.

sandros

[Tkalxx]

Hey Tkalxx

What battery did you go with? I've moved from east coast to Normal about a year ago and my options for sourcing a battery are minimal in my area. Thanks for any info.

sandros

Here in Canada options for batteries are pretty slim. I ended up getting the Motomaster AGM, it has 850 CCA which is more than the stock battery... beneficial for our cold winters. A lot of people on the forums seem to recommend the Odyssey brand though.

[rusllank]

Fellow Canuck here, I can attest to the weak battery fiasco. This morning, after I started the car, the engine sounded off and was shaking, accompanied by a blinking CEL. I turned it off to check what it meant and when I turned it back on, it was gone and the engine ran smooth. The battery I have is ancient, and it time for a new one. Just wanted to say thanks for all the info on this here thread