You didn't specify model year or engine type.
Whether it's a diesel or not that, unless it's a a really ancient model that engine is computer controlled and it really needs to be scanned with a good scan tool both for codes and to check live data to see what's going on in there. If it's a gasoline engine you can also bet the spark plugs are badly fouled from running under those conditions.
I would assume it's a gasoline engine and not a diesel, since he said he changed ignition coils. The RPMs also seem too high for a diesel as well. Our 1998 Ram 2500 Cummins turbodiesel redlines at 3,000 RPMs. A diesel revving like that would be scary, if not outright undriveable in my limited experience with them. Haha.
Good point, I missed that about the ignition coils!
Well realize modern diesels are all computer run fuel injectors are electronic and hydraulic there's all kinds of computer sensors for feedback. With that model you really have to find a guy like me with a dealer level scan tool to analyze the whole system. Guessing would be foolhardy it's obviously running rich of black smoke is coming out could be a problem injectors or a sensor feeding them too much fuel a zillion things can do that
He never said the engine was a diesel.
