Having a little problem with ignition coils going out on my 1999 f250 with 5.4 . What is the issue and how can I stop it from happening?

 

The first thing that comes to mind is , how are you determining the coils themselves are defective ?
If you switch the coils with different cyls , is the result the same?
Are you checking the interior connecting spring that goes over the spark plug for good connecting?
Are there any traces of spark jumping through the coil boots to ground?
Sometime questionable quality produces repeated results.
Are you or have you considered using Motorcraft coils?

 

coils on my 2009 F250 5.4 keep burning out. What voltage reading should I be getting from the alternator?? Also, what is the input voltage that the coils should be getting?