I have written these as an alternative to removing the driver's side kick-panel and the parking brake/hood release support bracket to get to the ECU on my 1993 F150. That method looked way too involved, so I decided to remove the ECU through the firewall from the engine compartment. Here's how I did it:

If you try these, you do so at your own risk! You can't blame me if something goes wrong or it doesn't work!

DO THIS FIRST !!: Remove the keys from the ignition and disconnect the battery.

Using a 10mm socket, disconnect the wiring harness from the ECU

Using an 11mm open-end wrench (or deep well socket) remove the weatherstrip from around the ECU. There are two nuts on studs connected to the firewall. Only the nuts come off. (no jokes about studs & nuts)

Using a 5.5mm socket, remove the 4 bolts that hold the outside of the plastic fender-liner above and behind (towards rear of truck) the front tire. The "inner" bolt with the huge washer is 8mm and is actually behind the tire- towards the engine.

You're not done yet. There's still one more 5.5mm bolt under the truck- behind the wheelwell.

Pull the ECU out the "front" of the firewall. You'll have to push the plastic fender liner (that you partially unbolted in the above steps) towards the front of the truck to squeeze the ECU out. Since I was working by myself, this is where I used the pry bar. I used the metal "lip" of the fender as a fulcrum to push the plastic out of the way. Be sure to protect the paint with a rag or something wrapped around the bar!!

The ECU is out. Not very impressive considering the work it took to get it out.

The end opposite the wiring harness connector is taped with a "warning" label. The ECU code is also shown here. I'm glad it matched the one on the door jamb!

Remove the tape and you'll see the edge connector. Clean this really, really good. I disassembled the ECU with T10 & T12 "torx" screwdrivers then used cotton swabs & rubbing alcohol to remove the white grease that is on the connector. My ECU did not have any other coatings (some have a clearcoat under the layer of grease). I used a little "emory" cloth to shine up the contacts, then installed the chip.

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