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Hi all!
I recently purchased a pre owned ‘15 500 Abarth with 50k miles from Carvana.
Purchasing was easy but their techs pretty much missed everything they “checked” in their multipoint inspection. Luckily I went through an apprenticeship program in automotive repair, but that was over a decade ago back in 05-09 and haven’t worked in that industry since.
So I was able to do simple things like oil and filter change, brake rotors and pads, Pcv valve and assembly.

Now I’m getting that sulfur/gunpowder smell from the exhaust which would be indicative of a bad catalytic converter.

However a bad Cat at 50k may as well be another symptom of an even shittier underlying problem (ie exhaust valve not sealing).
Will be changing spark plugs later today to see if caked up.

I also performed a “napkin test” to see if exhaust gasses are sucked up the exhaust, which again could be a tell tale sign of an exhaust valve not sealing. The results weren’t very helpful as I just got a slight back and forth pulsing when holding it near the exhaust tip.

I’m a little rusty when it comes to diagnosing so I hoping for some expert help and advice here.

2015 Fiat 500 Abarth (stock)
-Check engine light: NO
-Runs and starts w/o problems although running cold is a little rough (twitchy throttle feel) until engine warms.
-Seems to lose a bit of boost when pushed hard (normal mode goes up to 12 then drops inconsistently at high rpm, sport mode used to top out at 18 but now stops at maybe 16 and also loses slightly with increasing rpm).

Both Cat and/or head replacement are expensive. So I’m aiming to nail down where the issue stems from.
 

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Run the Italian tune-up.

And hope for the best. I wouldn't worry about it till it throws a code. Also, the boost seems to be pretty normal. Unless you can't really trust the reading anyway. Yours seems to be around the ballpark. The boost isn't the strongest at the high RPM, fyi necessarily.
 

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Nor-Cal PRK
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@LeeR500

Non-Problem.

You're burning off accumulated hydrocarbons on the CAT that haven't fully burned off because the car & CAT hasn't been driven hard enough to become red hot.

Last night I took a break from my Stelvio, and drove my wife's 500 to get us some take-out.

Took my favorite twisty back road, and was rowing through 5 gears in SPORT mode w/ the sunroof open in the beautiful 67 degree PRK evening, and smelled the same gunpowder smell. On the return trip from the restaurant, the gunpowder smell was substantially less than at the start. Bottom line: the wife babies her 500 :)

In conclusion - drive it Andretti style and the smell will get less each time you open it up.

Happy Thanksgiving!
 
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