ok ive just been given a 91 ford ranger that sat for 6 years.. it was a gift from my father... it had problems in the beginning like a miss which turned out to be bad plugs, wires and a faulty coil pack... but all that got fixed and i was driving it around and i came out onto a road and down shifted floored it and i made my turn only to hear a knocking noise and my truck was missing.... it only knocks when its under load and if u floor it at idle for a second but the miss is constant... any ideas?