Should I be concerned?
 

I took my 2016 A8 Stingray on a short trip on Nov. 4th. Ten miles in the engine started sounding rough and the check engine light was flashing. I was about 15 miles from my dealership so I drove it there staying about 50 mph all the way. They gave me a loaner for the night and checked out the engine the next morning. They determined it was just a bad spark plug. I'm getting ready to store for the winter so I filled it up and added fuel stabilizer on the 8th. On the 9th I took the car out for a short run (about 15-20 miles) and twice the exhaust blew smoke out like a fogging machine but no check engine light. I called my dealership and they told me no worries and that it was probably just the fuel stabilizer that caused the smoke. I didn't want to prepare it for winter without at least one more trip to check it out so I just went out for about 15 miles. Got on it about 10 separate times getting up to about 90 mph with no problems. But then I thought it sounded funny and hit it hard again and once again blew out a lot of exhaust smoke. After that it was fine. Should I be worried and what might be causing this? The engine sounds great right after each episode of the thick exhaust smoke. Weather here is about 40-45 degrees if that makes any difference.

As far as the exhaust, the LT1 & LT4 burns a little rich and will produce more “smoke” under WOT... and as the temperature drops, a lot of what you are seeing can be condensation burning off, especially if the engine is cold.

If that is all that you are experiencing, and you have no codes, then you “should” be OK.

BTW, I purchased the below a few years ago and it works great. If you’re curious about check engine codes, as well as a few other diagnostic matters, you might want to to pick one up... There are others, as well as several hand held devices too...
https://cimg2.ibsrv.net/gimg/www.cor...e8869218b0.png

I think you're fine. What you described is a mis-fire, which the PCM self-diagnosed and indicated with a flashing check engine light. The codes directed the shop to replace the bad sparkplug, and now (I'm assuming here because you didn't state it directly) the engine is running smooth.

Fuel stabilizer *can* cause the exhaust you're seeing, but I think it at least, if not more, likely that you're seeing condensation, as sTz pointed out.

Oh, and I've got a BlueDriver diagnostic tool as well. For $100 it's money well spent if you want to know anything that's going on in your engine.

HTH, and have a good one,
Mike

The problem occurs for a reason, not some dealer fantasy.

I've used fuel stabilizer in everything for years and never had the experience you have... in anything. There is a cause of your issue and I suggest you consider finding another dealer to go to. It is clear until something obviously "breaks" there will be no further action from your dealership. All the best!

:iagree: The same here if that much smoke came out from it. Could you tell if it was left side are the right side that the smoke was coming from.

This coming spring may want to get someone behind you to see what bank it is coming from if it does it any more. But I agree something just don't sound good. Plus the same as me on the fuel stabilizer it will not make your car smoke like what you are saying here. Robert

I couldn't tell which bank the smoke was coming from. It looked pretty equal through the rear view mirror. I believe the engine was warmed up enough and I didn't think it was going to happen again. The engine was running very smooth but then I could feel that something wasn't right (It sounds funny but I felt like I good feel the exhaust sounding rough and I kind of knew it was happening again) and when I hit the gas hard the smoke came out like crazy. No problems after that for the final 5 miles home.

I have used stabilizer for years. Never had the problem you described. I would get a second opinion.

To start w. your first post, you said the dealer diagnosed a bad wire, and they replaced it. Now, this is a '16 maybe built in '15 but still no more than 2 years old and a spark plug wire has gone bad. If one can go, why not another one?

Second, maybe the dealer knows about stabil more than I do, but I'm with the others starting w. Avanti. I've used it in about 4 cars and never had that happen.

Finally, you don't state where you live, but if there is another dealer, I'd go there.* I'd also start looking for a good indie shop that knows C7 Corvettes just in case some day in the future, AFTER your warranty is up and you need a good shop. Right now, you still have a warranty and those who say not to worry too much are possibly correct----for as long as you still have that powertrain warranty, that is.

* Normally, it's better to go to a dealer, or any shop, when the problem is occurring---that means leaving the engine running while you go inside and tell them the car has a problem. Not all problems throw codes. :cheers:

OP never said anything about a “bad wire,” but indicated that the issue was identified as a bad spark plug.

I just thought I would add that driving while your CEL is blinking is a risky prospect.

Driving while it's illuminated, but steady is usually not an issue, but when it's blinking, driving on it can damage many things, including, but not limited to the cats.

Autozone lends diagnostic OBD2 scan devices just have to leave a deposit which is fully refundable when you return it :thumbs:

:iagree:

Does not sound normal at all.

OP, what brand of fuel stabilizer did you use? How much did you put in? Did you have a 1/4 tank of gas before you added it then filled the tank?

Doesn't the X-pipe mix the exhaust from both sides of the engine?

I used 8 oz. of Sta-Bil fuel stabilizer in a full tank.

Condensation causing smoke? Uhhh, no.

With the engine at operating temperature if you experience sustained exhaust output resembling a fogging machine that isn't normal. Stuff like Seafoam can cause light to moderate smoke, especially if used in much heavier than recommended concentrations.

If you are getting a few brief bursts at full throttle this can be normal for a DI engine because they generate a lot of particulate matter which collects in the exhaust system (you of course see it on the exhaust outlets) and under heavy throttle buildup will exit the exhaust system. But these should be brief bursts that are not sustained under continued heavy throttle and they should lessen after a few full throttle bursts. It is quite possible you built up additional carbon in the exhaust system while driving it with a dead cylinder and this is responsible for your current bursts of material from the exhaust.

As owc6 indicated you don't want to keep driving with the CEL flashing because that indicates a sustained misfire in one or more cylinders that is dumping raw fuel in the exhaust unless the misfire is caused by an injector not opening. The EPA/OBD II requirements call for the CEL to be flashed when there is a serious issue and dumping raw fuel into the cats is a great way to start a vehicle fire.

:ack: *head smack too* Thank you. I must have "conflated" spark plug into both with a wire. :cheers: More than one plug, excluding wire? :D

I don't know that I would call it "sustained bursts". Looked like one big blow of smoke followed by a smaller amount and then okay. Engine sounded great but just before it happened I felt it turned a little rough or the exhaust sounded different (like it was stopping up) and then the smoke came out. After that it was fine. It has happened a total of three times now and I hate to winterize it and then have the problem in April. I think I'll try my dealership one more time. I am limited to this dealership. It's where I bought the car and the next closest dealer is about 30 miles away. Thanks for the information.

To the OP, I'm going to retract my original statement that I didn't think you have anything to worry about. Sorry about that, I didn't read the first post carefully enough.

With an A8, you have very little control over when AFM engages (manual shifting mode is the only way I know of). I have no idea if the following describes the cause of your problem or not.

You had a problem with a fouled/failed spark plug. The plug was replaced, but you're still occasionally feeling, IMO, a misfire developing. You run the engine hard, which gets the cylinder temps/pressures up high enough to clear the cylinder. You haven't mentioned the color of the smoke, other than describing it as a "fogging" machine, which is light in color.

Again, IMO, you may have a cylinder that, for some reason, isn't cleaning the oil off the cylinder walls sufficiently, and gradually fouls the plug.

Try this: Drive your car exclusively in manual shifting mode, and see if that changes what you're observing.

You might also keep a watch on your oil consumption.

HTH, and have a good one,
Mike

:iagree:

On multiple occasions I seen fuel stabilizer cause some odd "unexplainable" issues in performance cars until it was ran out of the system. I would have the plugs and wires changed and go from there.