I kinda got things bass-akwards..I guess I should show you all how to get at the ECM and what'* "In The Black Box" (actually, ours are bare aluminum
First off, to get to the ECM, you will need a 7mm socket, a 10mm socket, and a 1/4" socket. You'll also need an 8mm wrench or socket to disconnect the battery.
Open up the passenger side door and here'* what you see...
The ECM is behind the glovebox on the far right corner of the dash. You get at it by removing the two wing-nuts on the black trim panel (down near the carpet) and the two trim screws just behind the glovebox.
With that, the plastic trim panel will drop down. Disconnect the courtesy light and you can get the trim panel all the way down to the floor. The ECM is held in by one 10mm nut and a little plastic flap on the lower left corner. Disconnect the three electrical connectors, remove the nut, and the ECM can slide up, out, and all the way out from under the dash.
Now, to get at the calibrator prom, the little aluminum flap/cover comes off. Remove the two 1/4" sheetmetal screws and off it comes. Open the locking levers on either end of the calprom and it will pop out.
Since this is a little exploratory surgery for your amusement, I'll take the rest of the srews out of the ECM housing and you can have a peek inside: Here'* the circuit board. Towards the top is an aluminum heat-sink with all the driver circuits for the sensors and motors from the motor. On the right are some more of them. In the middle is the processor, some programmable logic arrays with Delco tags, and the socket for the CalProm.
Here'* the backside of the board...nothing much to note here, all the components are on the front of the board, the back is just solder joints and circuit traces.
Now, the stuff we are going to change is all inside the calibrator prom, so lets go pop the cover on one and take a peek inside. Four little platic tabs keep the blue plastic cover on the calprom. Gently pry them up on one end and you can remove the cover.
Inside, you find one 27C256 EPROM which contains all the software and data for the ECM (not much, it'* only 32K Bytes in size)
Next to it is a circuit board that runs the Knock Sensor. While this seems like a goofy place to put it, I guess it made sense to GM. Up until the mid 1980'*, the knock module used to be a seperate module on the firewall of the engine compartment. Then GM moved it to inside the CalProm. Probably to keep people from tampering with it.
Last two components, hiding underneath the knock module circuit board, are a pair of resistor packs that serve as the pull-up resistors for various sensor circuits.
Ok, time to read the EPROM...
Here I have the prom connected to an eprom burner/reader. I'm using Craig Moates'* adapter header to plug it into a standard 28pin DIP socket. Later on, I'll be butchering one of the proms to replace the EPROM with a 28pin ZIF socket to make swapping EPROMS a little easier.