Chip Installation Instructions

Motronic ML3.1 (Porsche 911 3.2L 84-89)


Before beginning, you will need the following tools:

  • An extended 10 mm socket (about 2” long), socket wrench
  • Small flathead screwdriver


The Motronic DME control unit is a silver metal box approximately 6”x5”x2” located under the left front seat.  It has the word ‘MOTRONIC’ either on a decal on top of the box or stamped on the metal cover.  Slide the left front seat all the way back, and also upward for electric seats. Remove the floor matt that covers the control unit.  Using a 10mm socket and ratchet, remove the four 10mm nuts and washers that fasten the control unit to the floor.  The wiring bundle is held in place with a heavy steel strap that is also held down by a 10mm washer and nut.  Lift the unit up and off the studs.


Holding the Motronic box in one hand, pull back on the steel-retaining tab that holds the electrical connector.  Disconnect the box from the wiring plug by rotating the box out so that it pivots away from the retaining tab.  When reinstalling, remember that the plastic hook at the end of the connector is installed first.


At your workbench, using a small screwdriver, straighten the ten metal tabs on the bottom of the box; remove the cover along with the white plastic insulating sheet and set them aside.  At the front of the board is the wiring harness connector block, and at the rear is a wire ribbon cable.  The boards are held together by two plastic male/female posts at each end of the wire ribbon cable, which unsnap. (Fig. 1)  The best way to separate these posts is to place a small flathead screwdriver in the slit on the female post as shown by the screwdriver tip in Fig. 1 and twist while gently pulling the boards apart.  You may have to use some force to separate the two plastic posts, and it is best to pull on the bracket between the plastic posts.  Do not pull at the corners of the circuit board or you could flex and break it!  USE CARE SO AS NOT TO PULL THE BOARDS TOO FAR APART RIPPING THE RIBBON CABLE.  Lifting the rear end of the board, slide the front end of it out of the wiring connector block.  Your board may be glued to the connector block.  If so, use care and gently pry the glue away from the connector block and wiggle the board out to release it.  Do not use any knives, razors, or sharp objects here or you could damage the circuit board traces!


Fig. 1
Fig. 2

Gently flip open the boards like a book and locate the socketed chip on the board that you just flipped over.  (FIG. 2)  It will be raised off the board a little more than the other chips, and if your car has the stock factory chip currently installed, it will have a silver foil sticker on it with a sequence of numbers reading something like 1267355xxx.


If your car is an early 84 model, your chip may be soldered in place, in which case, your chip will have to be desoldered from the board, and a 24 pin chip socket put in its place for easy chip installation and removal. If this is the case, we can perform this modification for you for a nominal fee. These DMEs are designated with Porsche p/n 911.618.111.01 or 911.618.111.03 on top of the box.

Before removing the chip, observe its orientation by locating the small notch at the end of the chip.  Your performance chip must be installed with its notch facing in the same direction as the original one was.  To remove the chip, slide a small screwdriver under the chip and carefully pry upwards, alternating ends frequently to avoid bending or damaging the pins.  (CAUTION: MAKE SURE YOU ARE NOT PRYING UP ON THE CHIP SOCKET WHICH IS SOLDERED TO THE CIRCUIT BOARD)  As you handle the chip, try to handle it by the black body, and not the metal pins. Place the chip you just removed on the metal cover to protect it from possible static damage.

Install the performance chip by again noting the orientation of the small notch on the end of the chip, and installing it in the same direction of the original chip.  There is also a small notch on the chip socket illustrating the correct orientation.  If the chip is installed backwards, damage to the control unit could result.  Install one row of pins in the socket, and push gently on the other side of the chip until the other row of pins lines up with the socket.  Press down to fully secure the chip, double-checking that all pins are properly seated.  Slide the top board back into the connector block, line up the two boards, and then press down on the top board until the two plastic posts snap together.  Replace the cover along with its white plastic insulating sheet, and reinstall the control unit.