Gets black from the exhaust when on open road?

Hello,

If I understand you correctly, you are getting black smoke out of the tailpipe and the smoke making the back of the vehicle black?

There are a number of reasons why you will get black smoke out of the tailpipe.
It could be due to shorter fuel injector, faulty oxygen sensor, failed fuel pressure regulator, bad mass air flow or manifold pressure sensor, vacuum leak, stuck open EGR valve etc.

Take a look at this helpful guide, it covers the typical reasons for black smoke.

https://www.2carpros.com/articles/engine-black-smoke

Go through this and report back to what you find.

If you have any questions, feel free to let me know.
Thank you.