No power, missing, poor mileage, black smoke. P1211 p0284
Having some trouble with my truck. It will run well for a while (between 20 min and 2 hours) then will begin to lose power, puff black smoke and chug along. When it's running fine, there is a slight miss, but I'm not familiar enough with these to know if that's just how they sound as I've only owned it for 3 weeks.
Once it starts to chug, it will throw a CEL. I can pull over and turn off the truck, letting it sit for 10 min or so then fire it back up and it will run decently for a while, but still not perfectly. The cel will also clear, but will come back pretty quick once I start going again.
Power loss is to the point of barely being able to move pulling a 6k lb trailer, but it will run 75 when it's running decently. Power loss is progressive over the course of 5-10 miles.
Injectors are stock and when I took it to a mechanic yesterday he thought it might be the #8 injector, which failed the contribution test.
Empty running 65-70 mph I got 12.75 mpgs and pulling this ~6k trailer, its looking to be in the 7mpg area.
Anyone have any thoughts? I'll keep thinking of extra details to help diagnos this, but that's about it right now. Thanks guys.