I have a post a fewe lines down describing my problem, but in a nutshell here it is: 1985 Chevy Suburban 3/4 ton 4x4 6.2L diesel "J" code. I am experiencing what appears to be a "missfire" on one of my cylinders. Occaisional small amount of black smoke at idle. I have a few questions on troubleshooting my problem. 1. I disconnected the air purge on the fuel filter and get a good flow of diesel when cranking.. Does this rule out the lift pump as the culprit because I get fuel?? 2. How do I test the injector pump? I see the two scribes on the block and the pump and they are aligned. Am I clear in my understanding that I can loosen the pump and rotate clockwise in small increments to determine ifr it is working?? What exactly am I looking for if this is the correct procedure? How can I test the individual injectors? I had not noticed earlier but SOMETIMES I get a small amount of black smoke at idle. Could this be due to a bad injector?? How do I determine if one is working??