Truck Repair: n14 cummins celect, n14 cummins, exhaust gasket

Question
I have a 97 t-800.  It just recently developed a miss (it sounds like a blown exhaust gasket on a gas engine).  With this miss, it had reduced power.  I tried to drive it so get it off the road, and after a long downhill run with the jake brake on the miss got worse.  It almost felt like the jake brake was hanging up.  It then began to bellow black smoke.  I shut it down, checked engine over, and then had to start it up to get it off the highway.  When I start the truck, it will blow black smoke, still has the miss, and without applying throttle will gradually idle up on its own to 2000 rpm.  

Answer
If it has a steady popping soung & a large black puffing cloud out the exhaust then an injector solenoid has stuck overfuelling a cyl.The only way to find it is with a water hose running water over the exhaust manifold to find the hottest cyl & that is the bad one.