BMW/Bosch Motronic 3.3.1 PCB overview

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Fred
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by Fred »

I'm coding, don't you two worry!

As for grounds, we want one for digital and sensors, and one for ignition, and one for injection, and perhaps one for accessories or perhaps combine that with injectors. You can run multiple wires, but there should probably only be the three or four connection points.

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davebmw
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by davebmw »

OK I thought I should post up the schematic of the BMW engine wiring harness to help put everything in perspective with the Type_B and hopefully give some ideas for grounding arrangements.
Image

Any questions don't hesitate to ask as I have dissected this harness in detail during the rebuild to find where all the various bits are located and how the cables are run.
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
RandomHero
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by RandomHero »

have to say though, the BMW is the odd one out for this. Most auto ECUs don't have the ignition drivers in the brain. Most have them in the engine bay away from the brain. I'm not aware of any other cars that are like that. BMW is also a bit different because it puts the brain in the engine bay too (albeit in a box). Sean tells me the bike ECUs also often have the ign drive in the brain. I'm still not convinced it's the right way to go though. It is encouraging to know that with correct grounding you can indeed make it work like that without interference.
Just an FYI but with cars I've worked on as an auto electrician this is not uncommon.
I've mostly worked on fords with MS and they all have had Edis inside the ecu.
Many German and French cars have the ecu in the engine bay, Infact some of the fiats the ecu is on the inlet manifold.

I've never seen ecus in so many crazy places and faults because of this, I also noticed alot of cars from 2001 had ecu faults.
davebmw
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by davebmw »

Its worth noting that most don't pay that much attention to the housing for the ECU.
My motor has its own bay approx 100mm high x 250mm wide and 200mm deep.
The cover has a rather nice seal all the way round with a drain flap valve at its lowest point to collect and drain any rouge droplets and a 20mm thick heat and sound insulating pad.
Inside the chamber I put a temp logger (I relocated from work) and here is what it found on 3 thermo couples after a 30 minute drive from work:

Average Temp Degrees C
Ambient 22.4 Measured in Ventilation plenum below windscreen
Chamber 27.7 Measured in the ECU compartment
Engine Bay 56.1 Measured engine side of the ECU compartment hatch heat shield

When you consider that after the obvious setup problems, heat cycling is likely to be the primary source of failures, causing fractures in solder joints and premature failure of components etc.
Not to mention that the temperature change will alter the value of components based upon its temperature coefficient, dry out electrolytic's and severely alter the frequency accuracy of timing crystals.
It makes sense to keep this sensitive piece of equipment off of and away from the big hot noisy vibrating thing under the bonnet.
preferably put it in the cabin with the driver where the weather is frequently fair or make provisions for its habitat to be ECU friendly.
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
WTDeuce
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by WTDeuce »

RandomHero wrote:
have to say though, the BMW is the odd one out for this. Most auto ECUs don't have the ignition drivers in the brain. Most have them in the engine bay away from the brain. I'm not aware of any other cars that are like that. BMW is also a bit different because it puts the brain in the engine bay too (albeit in a box). Sean tells me the bike ECUs also often have the ign drive in the brain. I'm still not convinced it's the right way to go though. It is encouraging to know that with correct grounding you can indeed make it work like that without interference.
Just an FYI but with cars I've worked on as an auto electrician this is not uncommon.
I've mostly worked on fords with MS and they all have had Edis inside the ecu.
Many German and French cars have the ecu in the engine bay, Infact some of the fiats the ecu is on the inlet manifold.

I've never seen ecus in so many crazy places and faults because of this, I also noticed alot of cars from 2001 had ecu faults.
The older Motronics in Porsches had the ignition system in the box as well. Only a few had an external ignition box of any sort.
Id have to look at my diagrams but I dont remember there being 400 ground wires either.
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Re: BMW/Bosch Motronic 3.3.1 PCB overview

Post by preludelinux »

interesting i have 2x siemens bmw ecu's ( from odb2 328i's) if you would like pictures of those , overall it looks about the same except it has an aluminum block that goes around the ecu , kinda like a heat pipe on a laptop ~same 88 pin connector ( transmissions also share the same connectors but keyed differently )
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