405 Mi16 Motronic 1.3 ECU revisions

[rhalkyard]

[similar question cross-posted to Facebook groups for good measure]

I recently picked up a 1989 405 Mi16, and found that it had a persistent check-engine light for fault code 54 "Internal ECU fault" which I gather means that the ECU's EPROM checksum is invalid.

I found a dump of a ROM for my ECU (0 261 200 161, Motronic 1.3 with cat), and burned that to a new EPROM and it is happy now, but I've noticed that there seem to be several different EPROM revisions that correspond to that ECU part number:

• The bad chip in my ECU is 1 267 355 730
• The version that I burned to the new EPROM is 1 267 355 697
• Another version I found later is 1 267 356 020

All three have the ECU part number 0 261 200 161 in their information block at 0x1F00, so they're almost definitely meant for that ECU. Looking at hex dumps they all have slight differences with one another, but I don't have enough insight into Motronic's data formats to know exactly how they differ. I also have not been able to find a good dump of the original 1 267 355 730 EPROM that failed.

This is mostly an exercise in curiosity since my car seems to be perfectly happy with the 1 267 355 697 EPROM, but I would be very interested if anybody knows anything about the differences between them, or can point me towards information that would help me understand it. In addition, I'd be curious to find a dump of the original failed EPROM to compare against my bad version and see what exactly went wrong there.

Just in case they might be useful to anyone (they were remarkably hard to find!) I've attached the two EPROM dumps that I found online for my ECU, plus a dump of my bad original EPROM in case anybody feels like dissecting it.

0261200161_1267355697.bin

0261200161_1267356020.bin

0261200161_1267355730_bad.bin

[SRDT]

I had both good bins but not your bad one.

I assume that your EPROM looked like a stock one from Bosch? There is some lone data at the very end of your bad bin and that's suspicious.

[Goce]

In my experience, the same ECU, the same part number, can have very different maps, i have 3 ECUs all the 161. This are the 2 spares and one in the car. All 3 of them make the car behave very differently. One of the ECU has been remapped and it pulls much harder and rev limit is higher than the 8 K the. Other one makes the engine worm up much quicker than the rest. And the one that come with the car seems to hold the revs after letting my foot off the accelerator, good for driving flat out but around town with 4WD tricky.

[rhalkyard]

On 6/13/2023 at 1:40 PM, SRDT said:

I had both good bins but not your bad one.

I assume that your EPROM looked like a stock one from Bosch? There is some lone data at the very end of your bad bin and that's suspicious.

Yeah, the ECU box itself had obviously been opened in the past, but the EPROM itself looked original - it has a sticker over the erase window with the part number printed on it, didn't look like it had ever been disturbed.

I noticed the two bytes at the end too - it looks like all the ROMs I have have them, and they're different in each - maybe they're a checksum? Maybe sometime this winter when I'm stuck inside with nothing to do, I'll start really examining them and try to identify the maps and how they differ.

[SRDT]

On 8 bit motronic the checksum is usually with the part number and software revision.

They talk a bit about it here:

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/alternative-tuning-w-a-r-megasquirt-etc/375887-documentary-motronic-1-7-diy-reverse-engineering/page6