I have a 1990 F250 4.9L and my truck having a hard time starting up on its own. If i use the cold start can it will fire right up fine and drive normal. But when i shut off the car then try to start it up w/o the cold start it wont fire. So i changed out the cap/rotor with some new plugs and wires. I also replaced both fuel pumps and all the filters. Now i check the Injectors to see if it had fire and the Injectors are showing weak spark. Anyone know the cause and how i can repair it?

Do you mean the sparkplugs have week spark or the electrical pluse to the injector has low voltage. I'm having a problem understanding what your asking.