I have a 2001 sport trac and when I bought it, it had the original battery in it. When you go to start it no mater the length of time it has been off, sometime you have to hold the key in alot longer to get it to start up. Some times it doesn't start the first time, but the second time you try it will, it was feeling like it was weak starting so I replaced the battery and it fixed the weakness but not the trouble starting. I replaced the fuel filter, belts, and battery. Does anybody perhaps know what might be causing this?