Ford Repair: 97 ford F150 WEAK SPARK PLEASE HELP, ford f150, volt meter

Question
i have a 97 f-150 with very weak spark to all the wires... the truck runs horriable and is missing all over the place.. i changed the wires and today one coil.... but the problem is still there i put the timing gun on the wires and they are all still all over the place some times it sparks and some times not.. also the volt meter in the truck is all over the place as well it goes up and down it like spikes all the time but the truck still starts up every time please HELLLP

Answer
I will assume that it is a 4.6.I suppose that if there is not enough voltage due to the alternator than this could occur.Have you're battery and alternator tested.Have you pulled any codes yet,if so what are they.If not then you need o one way or another.