2007 S6 5.2 V10 - Misfires/poor acceleration
 

I've had my S6 (w/ 75k miles) for about a year now and have just started to have issues with misfires and poor acceleration (especially when the engine isn't warmed up). I know that I shouldn't be getting on it when it's warming up but I'm talking slight acceleration to get to highway speed (while the temp guage is about halfway between cold and normal). As soon as I accelerate ever so slightly the engine/rpms hesitate quite a bit and I get instant misfire codes. The misfires codes have come back 3 or four times for mostly the same cylinders (2, 3, and 7). I've taken it to the Audi delaer once but can't keep going back since it's 75 miles away. They told me it was just bad gas and I should use a fuel cleaner. I'm not sure I believe that though becuase I consistently use fuel cleaners and always use Shell or Mobil 91 octane. The spark plugs were changed out at 60k miles also.

Another issue is that it's taking longer than usual to warm up (15-30 mins). I'm hoping it's just due to the cold (25-32 deg currently) but I also had a small coolant issue that may have to do with it. I got a coolant light, topped off the coolant (w/ the engine cold) and later that day the coolant overflowed. I checked the hoses and they were fine but then noticed the reservoir cap was broken in the seal area. I may have just filled it too much because after I replaced the cap, I had no further issues with the coolant. I continue to have the misfire/acceleration issues though...

Any help is appreciated!!!

Troubleshooting misfires generally starts with the ignition. Coil packs and sparkplugs would be a good place to start with that. Depending on the spark plugs (did you use coppers or plats or irids?), life cycle could be anywhere from 5k miles (coppers) to 30k miles (irridiums). Also, check the gaps on the plugs. Detonation tends to open them up after a few thousand miles.....

Coil packs are pretty inexpensive ($18-25 each depending on where) but seeing that you have a V10, it can range pretty high. Same with plugs. I would start by replacing all the coil packs and plugs. Find the partnumber, order on line and replace. They are probably the easiest thing to do on Audi's......

Thanks for the response.

I believe there was a recall on the coil packs but I'll have to check the service history to confirm.

Not sure what type of plugs I have. Just know looking at service history that the previous owner took care of it at 60k. Tomorrow I will check the spark gap on the plugs that are visible but there are four that are covered by hoses that I'll let the dealer examine. The V10 is crammed in there and I'm not wanting to break anything so far from the dealer.

Even if it was an item taken care of as a recall, coilpacks fail. All the time. If the plugs have 15k miles on them, you might as well change them out if you are taking them out. Just a thought.

I was hoping to wait a bit longer on the plugs but I'll try anything that may smooth out that acceleration. I have to replace the brakes as well so might as well do everything at once.

75k on the clock I would say your problem is carbon buildup. I went through this already around the same time. They replace coil packs and that didn't fix the problem. Then they opened her up and that was when they seen how bad the buildup was.

Here is a link to my THREAD on this.

Hmm I've heard of the issue but thought it was mostly the turbo engines that had the prob. I'll look into it with the dealer. I also drive spirited and use good fuel/cleaners so it could've been the previous owner if carbon is the issue

After the clean up on your vehicle did it perform better and get rid of the CE light? Also, what method did they use to clean up the carbon? Sand blasting?

Yes, performance improved and the lights were fixed. I do not know what the dealer did to remove the carbon.

It has more to do with direct injected motors. Because the fuel doesn't pass over the valves they do not get cleaned regularly.