Registered: Dec 1969
Location: Lac La Biche, Alberta, Canada
Posts: 198

First of all, many thanks to Chris Bennet and FR Wilks for their help.

Here are a few things uncovered about the 84 to 89 911 Motronic DMEs.

1) They are all 8051 microprocessor based.
2) The 84 to 86 ECUs used imbedded code in the 8051 with the mapping of fuel and ignition contained in the EPROM.
3) The 87 to 89 ECUs have all program and mapping code contained in the EPROM with the internal ROM of the 8051 disabled.
4) The 84 to 86 ECUs can be upgraded to use the code of the 87 to 89 ECUs by replacing the 24 pin EPROM socket (S701) with a 28 pin socket, adding an EPROM with the later code, and adding two jumpers, one to disable the internal memory of the 8051 (B700), and the second to allow addressing the larger EPROM (move jumper B702 to B703).
5) All of the semiconductors on the digital board are standard “off the self devices” with the exception of S700 (the CPU in the 84 to 86 with custom programming) and S100 (which is a custom op-amp which reads the flywheel sensors and generates an angular velocity).

They are:
S702 – 74LS373 Tri-state latch
S703 – ADC0809 8 channel a to d converter
S705 - 74LS02 gate
S890 – LM139 op amp
S704 – CD4049 hex buffer/converter
S100 – Custom flywheel sensor
S700 – 8051 CPU
S701 – EPROM (2716/32/64)

What next?

How different is the late 944 DME from the 911 DME? Are there any hardware differences, or could one be made into another by swapping software?

What about some of the BMW look-a-likes such as the Bosch 0-261-200-059? (These have been going in the $60 range on E-Bay)

The 944 Turbo uses a knock sensor (KLR) in addition to the DME. How much work would it be to incorporate the KLR in a 911 and modify the DME software to retard timing? (See Chris on this one!)

Tim