I have a 1984 f150 i6 and I am having trouble starting it every once in a while when I drive for about 15-30 minutes and turn it off for about 5-10 minutes. It starts turning over but won't start, then it stops trying to turn over... The starter, and battery are good the fly wheel is good... I put a new ground connecting from the battery to the starter, but I don't know what else to do.. Can anyone help me with this?