04 f150 Truck will not start after running fine for days on end. alternator and battery both check fine, then all the sudden battery will be dead when attempting to start truck. Truck jump starts fine and runs again for weeks at a time and then all the sudden will need to be jumpstarted again. Battaery terminals are tight and have been serviced with spray.

 

The next time you start it, disconnect the battery while the truck is running. If it dies then the alternator really is dead. I would also check all of the battery cables and the grounds. It could be as simple as a weak connection not allowing a full charge from the alternator. Best of luck. Let me know how it turns out.

 

Agree with the battery cables, spraying them with the stuff will not clean corroded terminals, remove and either wire brush or sand paper them, then reapply the spray stuff. If you feel this has been done properly, the next time it fails to start, turn on headlights and engage starter, if lights go out, battery is no good.

 

Don't remove the battery cables while the truck is running. That's the old way, it doesn't work like that anymore. Not only does the truck take more electric to run than they used to but also unhooking the battery while it's running can fry the alternator.