348 Motronic 2.7 Diagnostics Motherlode

After some urging from a fellow mad scientist, I decided to throw this up here for the good of the community in hopes it will help others.

While I have had this for years, I've never realized what this was, and only in the past few days while poring over all my files in an attempt to track down a misfire error, did I realize how incredibly useful it could be.

This is a diagnostic protocol for troubleshooting the 2.7 348 ECU inputs and all related components, excluding the ECU itself. This is done by testing voltage, resistance, and voltage signals at the pins on the ECU wiring harness. You'll see that all the proper V and R ranges for all these parts- temp sensors, TPS, grounds, relays, coils, etc. are all provided.

Testing at the harness also has the added advantage of accounting for wiring and connector issues in your troubleshooting. For example, your O2 sensor may be fine when backprobed, but a connection upstream could be loose, or shorted due to bare insulation, etc.

I've annotated the document a bit to explain a few things and provide some basic guidance. There is also a simple wiring diagram included to help identify the pins in your T55 harness and to track down some of those elusive grounds.

If you see any errors or omissions in my notes, by all means, please let me know. I don't want to spread any bad or misinformation. I'm assuming this is kosher to post, as there are many more detailed schematics, etc. in past threads. If not, mods please nuke from orbit.

Thanks, and enjoy!
View attachment 348MotronicDiagnostic.pdf

 

AWESOME John!

This will be of GREAT help for 348 brothers, and Mondial T owners, diagnosing electrical problems.

Just printed out a hard copy for myself.

Thanks!

 

Ahh...that is an old document from about 20 years ago AKA diagnosis sheet #13
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Yep, great doc, I've got the older sheet 13 that fatbillybob has posted. I made a 55 pin connector breakout box so I can run the engine with loom still effectively connected to each ECU in turn. I did it with tons of push on terminals, takes ages to connect...

......so I more recently bought an old BMW 318 ECU and BMW 318 wiring loom to cannibalise to use the Motronic 55 pin connector/socket to make an even better very low cost diagnostic break out box.

Bonus is that I can also use the same unit on my 993 Porker that I believe also has Motronic 55 pin

 

I figured it was something vintage. Nice to know the original source, thanks FBB. Was this a series of documents, or a single release? Would love to track down and order any others like this for A/C ECU, etc.

I managed to get a full Bosch Motronic shop manual for multiple ECUs, but it is more about the guts than the expected inputs. It does provide a great operation overview, though.

Dapper: My thoughts exactly. I was already shopping connectors from Mouser/Digikey to make a crude pass/fail test box for all the simple Voltage/Resistance levels. So.. many... pins.. though.

 

I guess that is the next thing needed, a breakout box for the Motronic 2.7.

 

I think it would be more of a convenience then a necessity. If I was diagnosing these on a day to day basis, a harness and breakout would be nice, but for an owner trying to track down a problem, walking the loom is not horribly inefficient.

Just solder some clips onto an old pair of multimeter leads, and build a few bridge cables, and you are in good shape.

A mating connector with a label showing the proper pin readings would be another nice midway solution.

As a programmer, I've been chasing another white rabbit based on those memory select pins.

 

You chaps might want this too then.

Its the final 3 pages of the document above but stitched together as one.
Sadly its quite low res, but it does allow me to follow the cables around.
View attachment Motronic diagram.pdf

 

Motronic 55 pin is used on so many other Euro vehicles its really cheap as chips to buy an old scrap loom and an old ECU from e.g. EBay, in order to cannibalise the plug from loom and leave just the socket remaining in the ECU. I think there are Citroens, Alfa Romeos, Vauxhall/Opel red top engines, BMW's, etc etc that use Bosch 55 pin. Alternatively Connectors can be bought through Tyco if you are trade. I'm going to fit my 55 contact pins/posts to the gutted-out case of the ECU, so it should end up really neat.

 

Any pictures of your homemade breakout box?

 

Thanks!

I have actually see the fold out version of that. It's quite big once opened up.

 

Oh, the one I made is quite low res, I'll have a go at doing a better one... but each step "print screen", stitch images, crop image, print as PDF - looses resolution.

 

No that is not part of diagnosis sheet 13. It is page L32 titled Fig.3A "injection motronic 2.7" of the WSM volume 2 andit is a big sheet foldout sheet so you can read it

 

Ernie, I'll dig out the old one this weekend and take some pic, haven't started the mods yet for the ECU carcass version but will snap where I'm at with the parts

 

I'm an electrical tech and that will be a big help to me. Thank you for sharing.