My 87 300SDL runs rough until the engine gets hot. I think I have a bad injector. What is the best way to tell which cylinder is not firing? Can I shoot the tempeature and tell? Help Please. Jack

Might be a tired glow plug. If the idle is rough long enough, loosen the injector lines one at a time until you find one that doesn't change idle quality. When you isolate the injector, swap with another cylinder (don't forget new heat shields) and see if the problem moves to the other cylinder. If it moves, the injector is bad. If it doesn't move, the cylinder or IP is bad.

Sixto
87 300D

Thanks I will try that tomorrow.