[lovich]

I wonder if there's data on the difference between engines with factory settings, and vehicles that have been modified to roll coal. My hometown had a number of people change their trucks to roll coal and it would get noticeably hazy in busy intersections

[zrobotics]

I used to work at a 4 wheel drive shop in a previous life- there are likely more modified diesel trucks out there than you think. The idiots that purposely modify trucks to 'roll coal' are a minority compared to owners who have bypassed pollution controls for increased reliability and fuel economy. A truck with the EGR bypassed or DPF removed spews more particulate than stock, but this isn't visually apparent. Most of the smoke from rolling coal is unburned fuel in the exhaust gas, this phenomenon seemed to be mainly restricted to younger people, especially oil field workers.

I know this is anecdata, but at least in CO, UT, WY area there are more modified trucks than what is immediately apparent, since often a truck w/ bypassed emissions equipment isn't heavily cosmetically modified.

[msisk6]

I live in a small Texas town outside of Austin. I think my diesel pickup is the only unmodified one here. It's really that common. The exhaust after-treatment and DPF systems are fairly complex and most owners just take 'em out. There's emissions inspections in this county, but diesel vehicles are conveniently exempt.

[alliao]

why do they take them out? and when do they take them out? when it broke?

[msisk6]

A bit late to the reply, but mostly it's perception: when the urea-injection exhaust-aftertreament systems first came out in 2013 or so there were a few reliability issues that dealers didn't do a good job of fixing. It's much improved now and my truck hasn't had any issues at all.

And, I'm sad to say, some folks just like the whole "rolling coal" thing and the ability to put out huge plumes of black smoke.

[lovich]

That's not even something I would argue. I guess my real question would be "what is the difference between a car that passes emissions tests and a car that is modified about 30 minutes after an emissions test"

There are a fair amount of people who will actively pollute because you asked/told them not to, and I wonder if they have a significant effect on the environment