Could it be the ignition module? I know my '91 needed to have that replaced a few times. It's pretty easy and I changed it in like 10 minutes but if that goes the engine won't start. Also, here is a way to possibly pull those engine codes using just a testlight:
http://www.troublecodes.net/Ford/
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www.TheMustangForum.com 
2005 GT
JLT CAI, Bassani cats, x-pipe and axle back, custom SCT tune, deep dish 18" wheels, Nitto 555 tires: 299.1 rwhp / 323.7 rwtq
1991 5.0L LX Notch
Currently restomodding