Problem during acceleration

[Milen02]

Hello everyone,

I am currently driving 2012 A6 C7 with around 130k miles running a dual pulley setup with HX and cold air intake. Today after driving up a mountain on a steep hill when I pressed on the accelerator the whole car jerked as if the acceleration was pulled back. I had a similar thing happen a few days ago after doing an aggressive 60-130 and right after doing another pull where the car did the same jerk at 150mph. So far after a bit of tests I’ve worked out the problem only happens at 3/4 or more throttle and it seems as if the car is cutting fuel trying to protect something. After doing a VDCS scan I don’t see any faults. I think it’s important to mention that ignition coils and spark plugs are fairly new and the car still has catalytic converters (I’ve got test pipes ready, currently waiting for my mechanic to be free). Everything is pushing me to think the cats are toast but I don’t see any errors for back pressure or anything.. Any suggestions?

Adding a video in case it’s helpful youtube.com/shorts/vqRAQwAXYlg

[gk1]

AFAIK sudden jerks are typically associated with fuel or spark cut.
I'd check your sparks since you said you just did them recently. IIRC the spark plugs can have some less-than-optimal installations and still work (perhaps not at their best) without throwing a single code.
In my case I had 3 new plugs 4 old ones (completely different design and heat range) and 1 plug not tightened all-the-way and the car ran mostly fine without any codes or jerking.

[f4m0u5]

Hello everyone,

I am currently driving 2012 A6 C7 with around 130k miles running a dual pulley setup with HX and cold air intake. Today after driving up a mountain on a steep hill when I pressed on the accelerator the whole car jerked as if the acceleration was pulled back. I had a similar thing happen a few days ago after doing an aggressive 60-130 and right after doing another pull where the car did the same jerk at 150mph. So far after a bit of tests I’ve worked out the problem only happens at 3/4 or more throttle and it seems as if the car is cutting fuel trying to protect something. After doing a VDCS scan I don’t see any faults. I think it’s important to mention that ignition coils and spark plugs are fairly new and the car still has catalytic converters (I’ve got test pipes ready, currently waiting for my mechanic to be free). Everything is pushing me to think the cats are toast but I don’t see any errors for back pressure or anything.. Any suggestions?

Adding a video in case it’s helpful youtube.com/shorts/vqRAQwAXYlg



you say the spark plugs are new, how new and what gap did you set them to?

I jave had this happen with spaek plugs woth too large of a gap. and when ancat was failing.
what tuning company do you have?

can you log with their data logging software when this happens?

Besides from doing a log, i would suggest not leting it happen till you fixed it because in the long run it can cause damage no matter whats going on.

What grts me tho is not even a missfire code when this happens or even pending codes...

[Milen02]

I didn’t install them and cannot tell, the last owner did about 5000 miles ago. Running 034Motorsports ECU and TCU. I could do logging, just not familiar with how to do it since I’ve only used the flashing portal to flash the tunes. You said you had the same thing happening when the gap was too large and a cat was failing, did you have any symptoms other than that nasty jerk. I’ve ran the car with stage 1 for around 2000 miles and the stage 2+ for about 200 miles and the first jerk was at really hard pull where the cats definitely reached high temperature. Then I didn’t have any problems with any acceleration (haven’t tried going over 120 mph though) and yesterday was when it started happening occasionally and every time I pressed the throttle hard.

[rey_reysA7]

Ya totally agree with starting with spark plugs. 3.0T is a bit picky.

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[f4m0u5]

I didn’t install them and cannot tell, the last owner did about 5000 miles ago. Running 034Motorsports ECU and TCU. I could do logging, just not familiar with how to do it since I’ve only used the flashing portal to flash the tunes. You said you had the same thing happening when the gap was too large and a cat was failing, did you have any symptoms other than that nasty jerk. I’ve ran the car with stage 1 for around 2000 miles and the stage 2+ for about 200 miles and the first jerk was at really hard pull where the cats definitely reached high temperature. Then I didn’t have any problems with any acceleration (haven’t tried going over 120 mph though) and yesterday was when it started happening occasionally and every time I pressed the throttle hard.



i would buy a set of the oem ngk plugs or go with the brisk racing plugs from 034. then try a gap around .027 ( previous owner did plugs stock not tuned so he mostlikely have left them at srock .032 gap)

https://www.rockauto.com/en/parts/ngk,94460,spark+plug,7212


you can remove rear o2 sensor and check n cats with a borescope if you want to check on them.


With spark blowout you would usualy only have a "jerk " under boost.


when a cat fails (depending how) its usually a constant issue. BUT when my magnaflow cat failed it melted into a chunk that would only block the exhaust flow under high rpm when it was pushed up against the cat outlet causing back pressure.



034 logging software is super simple. first time you setup logger i belive ypu need to have a internet connection. then just plug cable to car . load the logging software. then hit connect and it should pull up a new window with the logger and start logging automatically. In the bottom left of the logging software you will see a button to stop logging. then once the log is stopped it will change to "start" to allow a new log

[Milen02]

i would buy a set of the oem ngk plugs or go with the brisk racing plugs from 034. then try a gap around .027 ( previous owner did plugs stock not tuned so he mostlikely have left them at srock .032 gap)

https://www.rockauto.com/en/parts/ngk,94460,spark+plug,7212


you can remove rear o2 sensor and check n cats with a borescope if you want to check on them.


With spark blowout you would usualy only have a "jerk " under boost.


when a cat fails (depending how) its usually a constant issue. BUT when my magnaflow cat failed it melted into a chunk that would only block the exhaust flow under high rpm when it was pushed up against the cat outlet causing back pressure.



034 logging software is super simple. first time you setup logger i belive ypu need to have a internet connection. then just plug cable to car . load the logging software. then hit connect and it should pull up a new window with the logger and start logging automatically. In the bottom left of the logging software you will see a button to stop logging. then once the log is stopped it will change to "start" to allow a new log

Thanks for taking your time writing this.
Next week I’ll change the coils and spark plugs just to be safe since they’re not even that expensive and after that get rid of the cats overall since I was about to do it anyway. I don’t really see a reason to stress the car out even more at the moment by logging data when doing these things should fix the issue.

[jrsAudiA6]

Hello everyone,

I am currently driving 2012 A6 C7 with around 130k miles running a dual pulley setup with HX and cold air intake. Today after driving up a mountain on a steep hill when I pressed on the accelerator the whole car jerked as if the acceleration was pulled back. I had a similar thing happen a few days ago after doing an aggressive 60-130 and right after doing another pull where the car did the same jerk at 150mph. So far after a bit of tests I’ve worked out the problem only happens at 3/4 or more throttle and it seems as if the car is cutting fuel trying to protect something. After doing a VDCS scan I don’t see any faults. I think it’s important to mention that ignition coils and spark plugs are fairly new and the car still has catalytic converters (I’ve got test pipes ready, currently waiting for my mechanic to be free). Everything is pushing me to think the cats are toast but I don’t see any errors for back pressure or anything.. Any suggestions?

Adding a video in case it’s helpful youtube.com/shorts/vqRAQwAXYlg

I have the same year A6 as you, also with dual pulley and 034 ECU/TCU tunes. CAI, HX. My mileage is about 120K miles. I have not experienced what your short videos shows but I have had misfires happen both before and after going DP. Logging data such as spark advance, fuel pressure both low and high, boost etc should help isolate your issue. I have tracked my A6 a lot over the almost 12 years I have owned it. As a result I have had to replace both SC intercoolers, PVC, inter-cooler water pump, what I consider wear and tear items. Both inter-coolers were leaking, one worst than the other, and causing miss fires on the cylinder were the leak was occurring. I have recently replaced both my cats but only because the passenger side cat broke and the exhaust manifold flange. From your video I doubt that issue is cat related but probably still wise to check their condition. Badly melted cats have been known to cause internal engine damage if not caught early. If you are not misfiring than it probably is a fuel problem, maybe a clogged filter or low/high pressure pump failure. Good luck in identifying the issue.
One more thing. I am running NGK spark plugs that are 1 heat range colder than stock NGK plugs. I believe I have them gapped to .028". I did this more for insurance then addressing any kind of spark related issue.

[Milen02]

A little update. I got rid of the cats and the problem stayed, after changing the spark plugs and gapping them at 0.026 the issue got resolved.

[f4m0u5]

A little update. I got rid of the cats and the problem stayed, after changing the spark plugs and gapping them at 0.026 the issue got resolved.

glad its sorted!