Motronic ECU/DME help on SPECIAL vehicle

[Snobol4]

Hi Everyone. Forgive me, as I am new to this forum and quite new to the world of Porsche.

I have acquired a scratch-built off-road racing vehicle constructed in the early 90's that has been laid up in a barn for 20+ years. It utilises a Carrera 3.2 engine (I believe a 930/20?) and Motronic ECU. There is no Cat installed. I attach photos of the vehicle FYI and also the DME I need help with.

Fuel is getting to the rails OK under pressure an the engine turns over freely, but the coil primary is not getting pulses.

Can anyone here help me with the following:-

1) Does anyone have schematics that would match this model of ECU hardware they could share?
2) Are there many hardware variants of this Motronic ECU or is the hardware basically the same for (all/most) p/n variants? I understand that the EPROM holding the program/settings change for different vehicles, markets etc but does the electrical schematic stay the same? FYI the EPROM seems to be blank/faulty and appears from the label not to be original.
3) Does the EPROM merely hold the engine characteristics (tables) and the actual processor executable program held elsewhere (inside the MCU itself?), or does the EPROM hold both the program and the data maps?
4) If this unit is faulty, do I need the exact same model or is there a "range" of different DME part numbers that are electrically identical? I appreciate the correct EPROM would need to be installed for this engine. Could you even use a Bosch Motronic originally from another make of car, e.g. Mercedes and just change the chip?
5) You will see in one of the photos circled there appears to be some burning going on. Anyone familiar with what might have caused this? What is the replacement part?

I would be very grateful for any help anyone can give me. As you can understand, it's rather more difficult working on a vehicle that has been built up from unknown bits. The VIN number means absolutely nothing, so it's a huge learning exercise!

Nick



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[Synchro Joe]

You can find some basic information by searching on this forum. Looks like you're in the UK ?
https://forums.pelicanparts.com/porsche-911-technical-forum/106839-dme-info-please.html

[wazzz]

Motronic diagrams can be downloaded from here.
It's a zip file with diagrams for both the analog and the digital PCB. They are for the 87 Carrera model with a 2764 EPROM (28 pins), but almost identical to yours, which appears to be an 86 with a 2732 EPROM (24 pins).

Your injector driver current sense resistor is badly burnt. Hopefully it didn't kill the 0127 IC, which is no longer available.

To answer some of your questions, yes there are many variants of this Motronic ML3.1 generation for various cars of the era, and they are not interchangeable, as most other cars are water cooled and use different signals. But they all share some parts. There are Bosch ECUs for BMW and Opel/Vauxhall that are quite similar and use almost same parts.
Of course the program inside the EPROM or MCU is specific to each car and even to each region or variant.

For later years, starting with 87, all data and program is held inside the external 2764 EPROM and the code inside the MCU is no longer used. Your 24 pin version can easily be converted to a 28 pin version, once it is fixed. You just need to replace the 24 pin socket by a 28 pin socket, or add the four missing pins to complement the existing 24 pins. And change a couple of jumpers to make the MCU use the external EPROM.

There are quite a few members here that are very knowledgeable about this stuff, no doubt they will chime in when they wake up. I'm only learning. If you would like, I have edited the diagrams referred above with all signal names, so it is easier to follow and relate to external sensors and components. I can send you a copy of these or even make them available from my drive for some time. Let me know.

[mysocal911]

This typically occurs when the alternator over-charges the battery, i.e. a battery voltage greater the 16-18 volts.
Most likely the injector driver transistor has been damaged.

[wazzz]

Any update?
Bumping this up in case you need more help.