Chip replacement procedure for the Bosch 403 DME
WARNING: This is not for the faint of heart nor the mechanically challenged. The DME is a 4 figure component! Changing the DME chip may void your car's warranty and is to be done after arriving at the track and reversed before leaving unless you're trailered.
In the E34 5'ers, the DME is located in the housing behind the right front shock tower. Make sure the ignition is OFF. Remove the black cover held by 4 #3 phillips head screws and then lift the metal catch to disengage the DME plug. The plug will pivot on the engine side and lift out. Pull up the 2 spring clips securing the DME and then remove the DME.
With the DME on a table and with yourself fully discharged of static, bend the 6 tamper protection tabs around the outside of the DME. (This will likely cause warranty difficulties.) Remove 4 T15 screws from the top of the box (with 'Motronic' stamped on it) and remove the cover. Now you'll see a lot of surface mount components - the eprom is upside down on the top board.
To get the top board out, pull the center pin out of the plastic connector going through the center of both boards from the bottom of the DME. Pull (or carefully pry) up on the board at the back to release the 2 plastic clips (the plug I call the front of the DME). In the plug, at both ends, there is a clip which should be pushed in, towards the plug pins. This will allow the back of the board to be raised so that the board (and connector pins) can come out of the connector. To raise the board, you may want to straighten the wire connector between the boards at the back of them as you lift. I then pried (VERY GENTLY) at the front of the connector as I twisted and wiggled the board to get it out of the connector. Jim C. explained it as a ridge and a valley in which the pins sit.
Remove plastic cover of the eprom, carefully pry up eprom at both ends, install race chip. Reassembly is easier.