Yet Another Cheap DME Replacement

[ischmitz]

Digging up an old thread I am wondering if someone can point me to BMW DME boxes that have the same 3-row connector as the 964 boxes.

Tim, you seem to have a lot of info.

Cheers,
Ingo

[scarceller]

I just modified a 1986 BMW 535 DME part #0 261 200 059 to work in the 84-89 911.

This 059 DME had 24pin chip (4K Chip) in it when I got it, bought it on e-bay recently.

Here's what I changed:
1 - removed the 24pin EPROM Socket and replaced it with 28 pin. (You could simply add the missing 4 pins and not even remove the existing 24pin if you wish)

2 - added a jumper/bridge B700 (see picture)

3 - installed a 1989 Carrera chip.

The reason you need to add that jumper is so that the 8051 Processor DOES NOT use the internal code burned into the 8051. With the jumper in place the processor will read everything (code and maps) from the 1989 Carrera chip. The jumper simply grounds pin 31 of the 8051 processor.

Here's pics, but notice I use a 28c64b EEPROM and not the stock 27c64 UV-EPROM but either chip will work:




Now here's what I can clearly see is different and needs further investigation. The injector drive circuit is different in the BMW box, I will soon scope the injector line to see exactly how the injector pulses vary from the stock Porsche DME. This needs further investigation to be sure these DMEs work properly in the 911.

For now I can tell you the BMW 059 with 24pin EPROM can be made to run our cars.

[ischmitz]

Sal,

the injector driver in the 059 box is not PWM. Also it is missing the current sink for the switch-off spike from the inductive load. The driver is a simple Darlington and will most likely overheat when you increase the load signal away from idle. I am sure the DME will idle the 3.2 fine. But if you run it WOT down the straight it will get very very hot in there.

Modern MOSFET devices have very low RdsON values resulting in low losses and can deal with these complex loads. The older transistors weren't like that.

The 3.2 has all six injectors parallel and uses low-impedance versions - this is why Bosch had to use PWM.

Ingo

[scarceller]

Ingo,

Great info!

I thought the 86 BMW 535 also used lo-imp injectors, do you know for sure about this?

Also, were the BMW injectors in parallel?

I plan to look at the BMW wiring diagram but figured I'd ask to see what others may know.

I bought the DME cheap and figured I could use it for parts if need be so no loss on my part either way.

The other question is what about 944 DMEs?