Like the title says.. It's a 1996 F-150 4.9l 4x4 regular cab. Our oldest son swapped for this truck a couple weeks ago and seemed to have gotten a pretty good deal on it. Now out of the blue it's started blowing the maxi fuse at position 9 in the power distro box.

I've found a diagram that shows that fuse protects "Powertrain Control Module (PCM), PCM Power Relay, Electronic Transmission Control, Injector Pressure Regulator, Injector Driver Module". I swapped the relay with the horn relay just to make sure the relay itself isn't failing, and unplugged the PCM and blew the dirt out of the connection and plugged it back in. The truck ran all day yesterday without blowing fuse #9. Started it up and got halfway down the block this morning and the engine died. Blown fuse again.

I'm pretty good at following schematics, but need an idea of where to start. We don't have the money to lay out to have anyone else look at it, or even really buy the shop manuals, at this point.

Can someone please hold my hand and help me figure out what's going on with this truck?