By Peter Siposs

Several tuning companies have made performance chips for our cars. Dinan, Racing Dynamics, Jim Conforti, Turner, among others. The chip shown here is a Racing Dynamics chip I bought on Ebay. Chips are approximately $75-$375 depending on make and source. Chips are specific to the year/model/version of the car. More specifically the DME (Digital Motor Electronics) also known as the ECU (Electronic Control Module). For later engines like mine there is no mechanical method to change timing, so the chip re-maps the timing and fuel injection system to take advantage of higher performance than stock. The use of super unleaded fuel is usually required too. Claims of 19 or so horse power gains are pretty common. It also raises or removes the rev limiting safety features. Below is all the steps needed to change the chip. This example is from my 1989 BMW 635 but the same or similar techniques can be used on your model. Many 1996 and newer BMW's have chips which can be reprogramed rather than replaced. This are sometimes called 'Shark Injection'. Changing or reprogramming chips is usually one of the quickest and cheapest methods to improve performance. Often, when smog tests are required the stock chip will need to be re-installed first.
Caution: Use static safety precautions, and maintain a clean working environment.

Here is the old and new chips. In my case its a 28pin PROM.

Open the glove box and remove the upper cover plastic piece to gain access the upper underside of the dash. The ECU is mounted on the ceiling in the dash. Unscrew the four retaining screws to lower the ECU box.

After removing the attaching screws, bring the unit down to gain easier access to the multi-pin plug/socket.

The plug has a lever to release the plug from the unit. Release it and bring the unit to your workbench for chip fitting.

Turn the unit over and bend open the cover retaining clips. There are at least 6 of them around the unit.

Turn back over and remove the cover. The chip should have a retaining cover which just simply clips on. Lever it off. Its purpose is to prevent vibration and 'thermal creepage' from slowly loosening the chip in its socket. Note the location of pin-1 as identified by the notch on the end of the chip and socket. Using a thin small screw driver, slowly lever off the chip from the ends. Do a little on one end and move to the other several times till its free to prevent bending pins. Keep the old chip in a safe place in the packaging from the new chip. You'll probably need it to pass smog tests in the future.

The new chip MUST be mounted in the same direction as the old regardless if the label is upside down as in my case. Carefully install the new chip while making sure that all the pins enter their corresponding pin-socket. It may be neccesary to bend the pins by resting the chip on the bench with the chip on its side then bending the pins evenly at once. Repeat on the other side of pins. Reinstall the chip cover/retainer and close the cover and reinstall the ECU. Enjoy!

I took some 0-60 measurements before and after installing the chip. After 10 runs each I averaged about 1 second faster. Best time was 7.4 sec. I used a G-tech accelerometer to take the readings.
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Useful related links:

Back to my BMW 635 page
How to make front end frame lift
How to add a central locking switch
How to mount 6x9 rear speakers and a subwoofer
How to cure a fuel tank leak
How to fix your sunvisor mirror light
How to make a cup holder for your 635
Another BMW I currently own. An 81 320i.
633/635 (E24) Forum on the Web. Oustanding source of info from enthusiasts.
5-speed conversion process for 2002's.
Mesa Performance Parts - BMW/Porsche Parts
G-tech performance meter.

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