I apologize in advance for the long story in but it may be relevant. I am hoping for a little insight from those more experienced than I. Here is my trouble. My wife has a 2002 Ranger XL 3.0. She was recently stranded at work. The engine cranked over hard but would not fire up. I came to her rescue(no choice really) and jumped the truck with my bmw. It fired right up. Turned it off and back on and it fired up again. Several days went by with no trouble, then it happened again. Same place, at work. Her co worker tried to jump the truck with his Hyundai, no luck. I drove there again with my bmw and it fired right up. This time though, the gauges were twitching. I assumed it was the alternator. On my day off I took the truck and got stranded in a parking lot. It cranked hard but rough idled and died several times. I had all my tools just in case. I pulled the alternator and had it tested at the parts store. They said it was good and it must be a bad cell in my battery. I put it back in the truck and pulled the battery, had that tested and they said the battery was good as well. I then replaced the ignition wires and the truck, after a few attempts with jumping, fired up. Got it home. Next day it cranked hard but did not fire. I jumped it with the bmw and drove it to do some errands. It started fine the rest of the day. Next day my Wife got in it to go to work and it again cranked hard but did not fire. I then cranked it and held the key, stopped and then tried again, it fired up. So now I am puzzled. Should I replace my coil pack? maybe spark plugs?(I know I should have replaced them when I replaced the wires, but it was dark and I was stranded) What else could It be???? BTW, this all started with the unusually cold weather here in Las Vegas....