brcorp

What are the specific differences between the 84-86 and the 87 DME controller. The 84-86 unit has 24 pins on the E-Prom, some 87's have 24 pins while others have 28 pins. Is one better than the other, in that it offers more control?

THANKS!
Bill
1987 Carrera

Steve W

There really is no difference in the DME controller. The 84-86s were wired only to read 2k of an eprom, while the 24 pin 87's were jumpered to access coding in a 4K eprom. You can convert an 84-86 box to read the 4k eprom via jumpers, and it will still retroactively read the 2k ones. In the 28 pin 87-89 DME, the 8051 processing code was moved off a separate chip on the dme board, into the larger memory of a 28 pin 8K eprom. However you can also convert the 24 pin DMEs into a 28 pin one by the addtion of a 28 pin socket and some jumper changes. In the 28 pin programming, Porsche raised the idle programmed in the eprom from 800 to 880 rpm. In addition, the larger memory allowed the storage of multiple maps for different regions of the world to be stored all in one chip. Porsche probably did this to keep inventory under control. This means some of the 28 pin chips contain the coding for both the U.S. spec cars, and the European ones too. With respect to operation, the chip mappings in all years of the car are very much similar. A few years back Bruce Anderson did some dyno testing using different DMEs versions on the same motor, and found no differences in power.

brcorp

Thanks for your reply Steve. You answered my question.

Bill