Hi Nigel
I do know exactly what you mean. And certainly do follow all forementioned by you. I nearly wanted to qualify this, with an owner, of a similar vehicle. Is yours turbocharged?
That being said, still seems a bit much, regarding the amount of carbon. Do you have any idea, if the turbo, could allow engine to run slightly rich, during initial boost? Years ago, I had the necessary instruments, to observe air/fuel on my own, where I could qualify mixture at various rpm's. I guess I would be more comfortable then. As vehicle approaches 20k miles, I'll probably analyze the oil, through the Amsoil lab. I'm a long term dealer of Amsoil, and have been Since wrench turning days were over.
I was actually a "tuner", before there was such a term. Owned, a tuning shop, that specialized in muscle cars, all 50's V8's, and any performance foreign iron. Any electrical work. And distributor work, on ANY distributor, of any vintage vehicle. Foreign distributors, only stuff sold in US. I race prepped, power tunned for hi per American stuff. In those days, dyno was not so common, as it is now. The Sun machine, was state of the art then.
My personel specility was what was then, called pure stock. I had a number of cars, some mine, some customers, that I tweaked, enough to compete at regional/national level. Now that's pure stock, not pro stock, of course. I lost interest, in drag racing, with advent of bracket racing. Being an early street racer, back in the day, head to head, was the only thing of interest to me.
Haven't tuned though, since early '90's. Then did engine failure analysis, to supplement me after I closed shop, n started the Amsoil distributor.
4 cyl stuff is new to me. This is first I've owned. I have nothing in my profile though, to tell some of my auto past.
Hoping you have some further thoughts though.
As a last point, knowing what you said in your reply, is that in the many vehicles I've had, say since 1980, upward. Neva say black, dark grey, n lighter. But never, where it's kinda cacked on, (like a bit thick ). That's what prompted my post.
Tell me a bit of your Fiat ride, engine, mileage, up, etc. As I am novice to this.