firing

hi wayne, There could be so many problems with the engine it's practically impossible to list everything here. Your best bet is to take it to a mechanic to get it looked at. I noticed in the title of your question you wrote firing. Are you looking for the firing order of the cylinders?

fuil sending unit

Check three things. you need fuel, air and spark. check for all of them if you dont have one then your truck wont run. if you have all three, then you should check your timeing.

what motor do you have

cehck if your distributor rotor if it doesnt turn while your cranking your engine your timing gears are stripped out.