My gran sons 7.3 "diesels" after turning the key off. Any ideas as to what is causing this and how to fix it? Thanks

 

what 7.3 is it. powerstroke or IDI?

 

It is a 1997 F 250, so I assume it's a Power Stroke. Thanks

 

ahh, cant help ya then. i only know the idi engines.

 

First question:
Is there a remote start, Turbo Timer or Alarm system on this truck? If so, were any of these just installed on the truck?
If you answer YES to any of these, look at the wires related to these items or take it back to the installer of these item(s) to have them fix the truck.

If you answered NO above:
I would guess that its a short in your ignition switch or the wiring that leads up to the switch (Not the ignition lock cylinder).

I would replace the switch first to see if this corrects the problem because it's only $30.

If that didn't fix it your best bet is to look at the large wire harness on the back of the engine. First look for a small wire harness up in the valley pan that leads to the back of the engine and connects to the larger harness. This intersection is were you should start looking. If this whole area is diesel soaked, look for bad insulation from rubbing or pinching on the wires in the harness.
Hope this helps.