won't start when hot
 

97 mustang starts good cold, won't start when warmed up. have to wait 20 minutes before it will start.

Need more info.

Won't crank?
Cranks but no start?
Starter engages the flywheel but the crank won't turn.

If the last one is the condition it's probably a weak battery,dying starter,or poor ground.One reason is the starter motor has higher resistance in the windings when it's hot.This raises the voltage required to turn the engine with the starter.Poor grounds,a weak battery,or a bad wiring connection all cause higher resistance also.

Have you been messin with the timing? Could be to far advanced.

Check your air filter. Dirty air filter can cause what you described.

coil(s)?

i'm another one for the coils. coils can act up when the motor gets up to temp. just a thought.

bad starter/ starter heat soak??