ldamelio

Driving to the track yesterday in the early morning dark - the air was a little humid and misty on a stretch of empty interstate. PDK car in Sport mode, drivetrain and exhaust are stock. I put my foot into it somewhat to accelerate - nothing crazy - maybe 5000 rpm. When I lifted (with the accompanying pops and burbles that occur in Sport mode) I saw a trail of orange sparks out the back of the car. I was able to reproduce this a couple of times; it did not occur in standard mode. I've had the car almost five years and have never seen this. It was running flawlessly and did so at the track all day. Anyone ever seen this? I'm thinking it was the visual result of the pops and burbles (unburned gas igniting in the exhaust) and the proper atmospheric conditions.

rp718

Did you actually see sparks trailing your car, or just notice an orange glow in your rear view? Unburned gas would not leave a trail of sparks, and besides, if you were running that rich your check engine light would be screaming. Sparks mean something metallic, but if you ran well at the track your heads sound intact. I'd guess something in your suspension or axle shaft/joint assembly is metal on metal, or at least making contact under the right conditions. You might also want to check for some kind of metallic clip or cable that may have come loose and is contacting something else that is rotating.

ldamelio

They were sparks, not an orange glow - best way to describe it is that it looked similar to the orange sparks you see when someone throws a lit cigarette out a moving car window at night or a very minor Roman candle. They were at about spoiler/top of body height. Only at throttle lift in Sport mode. Nothing overtly loose - car was up on a lift the day before for a detailed tech inspection - I was under there along with two experienced track inspectors.

Dyim

First thing I would do is to have someone drive slightly behind and beside you and see where it is coming from. Or straight behind you with no lights if possible, so it is easier to see the sparks.

Or put a GoPro in the rear bumper.

ldamelio

Good idea, but it only happened twice and weather conditions were unusual. I'll try to reproduce it next time I drive at night; if I can then I'll do this.

rasetsu

Only reason I could think of is if the catalytic converter substrate is breaking apart.

MaddMike

Back in my rotary days I would shoot 6 foot flames but sparks is something else. Was there possibly something being dragged by the car?

Scrounger

Agree with Rasetsu. Sounds like the Cat is breaking up.

ldamelio

Thanks, this makes sense. Normal wear and tear (5 years/32k miles)? Track wear and tear (23 days)? Any consequences? I could care less if the car runs fine. If it fails emissions/needs new exhaust, I'm fortunate to live near both Fabspeed and Soul.

rasetsu

Not normal at all but also not the first time to have happened on a car. Yes, could be major engine failure consequences if it really is the cat breaking apart. Back pressure could send pieces back through the the turbo or even the cylinder heads.

modifieda4

i don't see that happening.

ldamelio

OP here. I've done my research on cat breakdown (if that's what happened - haven't seen it since and car runs and sounds perfect). If indeed that happens, it will give me an excuse to visit Fabspeed, but it won't do anything catastrophic. For now I'll keep looking for the next apex.

rasetsu

The reason I wrote what I wrote was that it supposedly happened to me with an early 2000s Nissan Altima. Car kept throwing a check engine light. Dealership kept it for a couple of weeks and ultimately replaced the entire engine under warranty. Service advisor word and document stated that faulty catalytic converter break down caused engine cylinder scoring. I say supposedly because I didn't see the damage myself but I would think the dealership would have needed to have detailed documentation in order to get approval to perform a full engine replacement. Now online sources state this isn't possible but I had an engine replaced under warranty allegedly due to this so I don't know.

modifieda4

I understand your experience, but for a piece of metal to flow upstream against the exhaust flow, from the cat, past the turbo, through the exhaust manifold, past the exhaust valves to get into the cylinders seems like a stretch. unless unburnt fuel in the cat detonated with enough force to send shrapnel upstream. most likely a clogged cat would create alot of backpressure resulting in bad performance and an inability to start.

blue17

That was a Nissan. They cheaped out on parts. I worked there when that happened.
This is a Porsche. Much higher standard. Night and day.