DME differences 1984-86 vs 1987-89

[shoguneagle]

I was wondering what the differences in the DME's are between the years 1984-86 and 1987-89. I know the pin number changed but what is the exact differences in detail??? Can the 1984-86 DME be used in a 1987-89 car and vice versa.

I am in need for another DME and several people have told me that the 1984-86 DME will work in the 1987-89 cars. I do not know why it would not work except for the expanded pins.

Can some one provide insight to this question??

Steve Hurt

[Quicksilver]

Yes the 911 DME's will interchange. As you have noticed the big difference is the later DMEs switched from 24 to 28 pins. The internal layout changed throughout the run of the 80s Carreras but the important bit is the maps in the chip was updated too. These can be swapped so it isn't a huge deal. Assuming you are talking about similar number of pins you can move your chip from one DME to another.

When they switched to the 28 pin DME it changed more then just the mapping. The processor on the 24 pin DMEs has the programing (not the mapping) burned into the processor chip. This limited what Porsche could do with it because the programming had to be compatible with all the DMEs back to 84. With the 28 pin DME they added a jumper that disabled the program burned into the processor and makes the processor run it's program from the ROM. This means they can change the code so they could make more refinements to the mapping. The mapping on the later 28 pin DMEs allowed more granular refinement so people often say they can feel a little more smoothness. In addition Porsche had learned more after 4 years of making the system.

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If there are changes to the reliability, component cost or some other detail between the early and late DMEs then that has never been discussed here.

[shoguneagle]

Thanks, Quicksilver!!!!

The information you have given provides a clearer insight into the differences. It is nice to know I can use a bigger number of years to replace my DME. I also appreciated your comments regarding costs, reliability, or other details between early and late DME's.

Thanks again,
Steve Hurt