No power, missing, poor mileage, black smoke. P1211 p0284

[toddman35]

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.

[firefighter317]

P0284 is for cyilnder 8 contribution/balance fault. P1211 is ICP not controllable - Pressure above/below desired. P1211 means the injection control pressure regulator failed the self test and te engine is operating in open loop due to not maintaining desired pressure. What kind of oil are you using? The wrong viscosity oil, fuel problems, faulty IPR valve, HP oil system leak, faulty HP oil pump, or faulty PCM can cause P1211. P0284 can be caused by bad rings, failed injetor, valves, push rod, rocker arm bolts, or connecting rod. Did the mechanic do an injector "buzz" test (electrical test)?