Misfires, and has excessive fuel pressure

We need to start with checking the actual fuel pressure to see if it is high.

This does sound like the issue because if you have dark or black smoke then that is due to the engine running rich.

https://youtu.be/peh7-pFycyc

So, I am attaching the process below on how to check the pressure, but your vehicle is slightly different in that this is high pressure system.

They use a common rail fuel system, so they don't have an actual spec, but they have you check the base pressure and then measure the difference from that base reading to determine if it is high or low.

I attached the details below for this.

So, once we know if while the engine is running the pressure is higher than that we can follow the testing. Basically, it sounds like the pressure is high, so we need to make sure the return line is not kinked or restricted.

If it is, then that is the issue and not the regulator. If it is not, then I would replace the regulator.

Please take a look at this info and let me know what questions you have.

Thanks