BMW/Bosch Motronic 3.3.1 PCB overview

[davebmw]

Hi All,

I wanted to show you all what the layout for a Bosch ECU looks like on a 93 BMW 325i.
And following a conversation with Fred in which he was shocked to find that they had dealt with the driving of the COP's in the same case as all the other sensitive bits and bobs.

This PCB is taken from a spare ECU i bought to rob the connector for my FreeEMS projects.
the pink section is the 6 Bipolar transistors used to lowside drive the coil packs.
The device outlined by the blue area is used to drive the 6 ignition transistors.
The green area contains drive for the injectors and all the other actuators and valves all low side drive.
The orange device is where the program and maps are held (duh!).

It may be worth noting that the ignition has its own ground all the way back to the head as does the injectors and the sensors all have separate grounds back to the block some critical ones are also screened one end, e.g. O2 sensor, spark sense and knock sensors.

So for all you non believers, some OEM harnesses are suitable for adaption to FreeEMS and MegaSquirt2 having already thought about the possibility of RFI from the inductive bits.

[Fred]

And following a conversation with Fred in which he was shocked to find that they had dealt with the driving of the COP's in the same case as all the other sensitive bits and bobs.

Thanks for the chat Dave, it was most enjoyable indeed :-)

Thanks for posting up the pics too. I 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.

So for all you non believers, some OEM harnesses are suitable for adaption to FreeEMS and MegaSquirt2 having already thought about the possibility of RFI from the inductive bits.

Careful, an unmodified MS unit hooked to three lighter than MS-required wires that are then hooked in parallel is not a good thing to have. Perfect for freeems, sure, perfect for ms, not without the sort of mods you've done. I just thought it best to qualify that :-)

Tell me, where does the connector go?? I can't see how it works. I'm guessing that there are two bus bars between the drivers to conduct the heat away. It would be nice to see some of it assembled too at some stage.

Cheers,

Fred.

[davebmw]

It was a nice chat there I must admit I was a little nervous about chatting with (for all intents and purposes) a stranger but after the call I can say that you sound like a stand up gent.
My wife and I have agreed that when we move into our next house in about 8 months we would like to invite you and your missus over to wales for a BBQ before you jet back to NZ as a kind of going away party / Freds 30th / us moving into a new house party.
The offer is there if you are interested.

Oh and yes I forgot to add that my MS2 is way beyond standard now thanks for adding that it kind off slipped off the gray matter!

The connector is along the top edge you can see the 88 holes with various pitches. Yes there are 2 aluminium bars that are clipped to the devices and bolted down to the aluminium base plate everything has plastic retaining frames to prevent any kind of movement.

Oh fuck it i'll go and get the complete one off the car..... back in 5 mins

[davebmw]

I'm back.
Ok the complete unit look like this:



The 88 way connector:


top down shot, notice the sprung clips holding the power devices against the aluminium bars, These bars are also bolted down to the base plate with enough contact area to dissapate the bit of heat that is generated.
The bars are used to bolt the lid down in 4 places.
There are also plastic holder/spacers that keep all of the devices in exactly in the right place and held against the silicone insulation pads.



angled shot:


The 2 together.


and as far as this ECU design goes all of the Bosch motronic series have the coil drive transistors in the ECU as far back as '88 where they only had a single coil and normal dizzy.
the way they get away with it is to use separate grounds for the power and digital/sensor stuff, very much what I have done to modify my MS2 and what I'm designing into version B of FreeEMS.

Oh and the PCB dimensions are 160mm by 120mm so hopefully this will be the size of the Type B FreeEMS.

[Fred]

Those connector holes stand out like a sore thumb now! I guess my eyes were just drawn to the smd resistors on each side when I first looked... woops.

I agree with robert on the multi grounds thing. I was thinking one dirty one, but you've convinced me that 3 grounds are a good move (you listening Jared?? :-p )

It's good to know anyway, because I DO want on board ignition for general use, but I want it done right (even if I won't use it myself).

It was a nice chat there I must admit I was a little nervous about chatting with (for all intents and purposes) a stranger but after the call I can say that you sound like a stand up gent.

LOL, I'm glad I measure up! Sorry for my larger than life/big mouth approach, as you can see, not a whole lot different to my approach on the forum...

My wife and I have agreed that when we move into our next house in about 8 months we would like to invite you and your missus over to wales for a BBQ before you jet back to NZ as a kind of going away party / Freds 30th / us moving into a new house party.
The offer is there if you are interested.

Sounds good to me! Make sure you book in at least 4 weeks ahead so that we don't overlap any europe/canada ski trips or anything...

Cheers,

Fred.

[davebmw]

I DO want on board ignition for general use, but I want it done right.

We'll there's not much engineering involved in getting it wrong! we have to do it right or be laughed at by the MS3 guys! I'm not up for that kind of abuse!

Sorry for my larger than life/big mouth approach, as you can see, not a whole lot different to my approach on the forum...

Never appologise for telling the truth, if someone cant handle it then they are probably a pathological liar or a bit limp wristed!

Sounds good to me! Make sure you book in at least 4 weeks ahead so that we don't overlap any europe/canada ski trips or anything...

Excellent, Will do!

[Fred]

Sorry for my larger than life/big mouth approach, as you can see, not a whole lot different to my approach on the forum...

Never appologise for telling the truth, if someone cant handle it then they are probably a pathological liar or a bit limp wristed!

I guess I meant the way I perhaps may have interrupted you a few times and talked about myself excessively, I don't mean to be rude though. It just kinda happens :-)

[davebmw]

Fred..... you worry too much! now stop being a mincer and get back to coding

[jharvey]

I agree with robert on the multi grounds thing. I was thinking one dirty one, but you've convinced me that 3 grounds are a good move (you listening Jared?? :-p )

Oh what, sorry I wasn't paying attention.

I agree, multiple grounds is very important. I'd say a min of 2 for dirty and 2 for digi/sense, perhaps 2 for sense would be good any how. I say 2 for each because you should have them at different lengths, and different ground points. I'd say an absolute min of 4, but really should be a min of 6.

However I don't want to stop there, I think many problems arise due to grounding issues. I just opened the layout, click the GND net, and counted 16 ground locations, so I don't think it will be hard to get the 3, 4 or 6 in there.

Fred..... you worry too much! now stop being a mincer and get back to coding

I'll drink to that.

Nice pics Dave. Must have been a bear to get that connector out.

[davebmw]

Nice pics Dave. Must have been a bear to get that connector out.

Hot air pencil and lots of patience, the board has 4 layers and huge ground planes!