[Diy_efi] Re: Wire up of BMW M3 coils...?

[Mike]

Hi Gerard,

Not sure why you are emailling me, we have a list so people can
respond if they want to, I think you misunderstood - I *dont*
have am M3. I am on 9 tech lists and a few social ones and keep
things fairly well filtered so I am up to my ears in emails...

It also seems you've answered some of your own questions in your
speculations and you seem to know what to do to set one up on a
bench and see if it fires. So go ahead and fire something up
and if it works fine if not then ask the list. Also I'm not
sure what you are trying to achieve, to learn about M3 coils ?
then go see BMW or experiment - I really dont see how I can
help you when the list - that has more intellectual muscle
then me - has more experience in identifying components
from other vehicles - I dont have an M3 and there are bound
to be a large number of varitions in ignition systems design.

If it was me, I'd construct a bench setup and experiment
to get a spark after either asking BMW for a schema and/or
going to the local reference library for a workshop manual
extract.

rgds

mike



At 10:41 PM 18/2/2003 +0200, you wrote:
>> mmm, And here was I wondering the list was dead...
>> 
>> Similar to the setup on my VL, cept 1 is signal, 2 is ground
>> but +ve is through wiring looming already. I'm replacing
>> my 500v NPN transistor with a mosfet driver as the saturation
>> voltage with be lower so well see what happens in a few days,
>> 
>> tah for the info - though I dont have a M3 (yet)
>> 
>> rgds
>> 
>> mike
>
>Hi Mike,
>
>I was wondering if you'd be of some assistance to me. I have had some
>coils in my possession for about 3 months now and not too clued up how
>they work. That's why I was querying the EFI list regarding M3 units.
>
>I'm going to throw some ideas your way, could you let me know if I've
>got my story right or should be shot for what I am thinking.
>
>First of all, these coils are 3-pin items. I can't even find connectors
>for them. I cut one up recently and it contains now extra funny
>electronics, just a plain simple coil it seems.
>
>I've run a continuity test on the pins, casing and plug-top connector at
>the high voltage output point of the coil. Here is what I have found:
>
> pin 1 and pin 3 are connected, but not connected to
> anything else (i.e., no path to casing ground or plug
> connection point
>
> pin 2 is connected to the coil mounting point/tab and
> connected to the plug connection point
>
> resistance from pin 2 to casing mount is around 0.8 Ohms.
> resistance from pin 2 to plug point is 10.8 KOhms.
>
> resistance from pin 1 to pin 3 is about 1.1 Ohms
>
>From this I deduced that pin 1 and pin 3 are wire-ups for the primary
>coil. Pin 2 must therefore be a separate +ve feed for the secondary coil
>and this continuously "vents" to the casing ground until the secondary
>fires the plug.
>
>If I recall correctly the primary was wound anti-clockwise down metal
>core, but doesn't give me much clue as to which of pin 1 or pin 3 is the
>+ve feed or the -ve feed.
>
>Pin 1 or pin 3 must be a ground signal from the ECU to charge coil. I
>guess maybe not such a big issue which way round, but it'd probably lose
>some voltage if the plug fires the wrong way.
>
>Now, looking at the pins out I saw on diy-efi regarding the M3 coils and
>your VL items (what's a VL, by the way? :)), I would reckon the +12v on
>those M3 items is for the secondary, the ground is to the ECU and that
>pin 1 (signal) is therefore a +ve feed. Is that right?
>
>Unless ofcourse those M3 things use some form of internal transistor to
>hook the +12V to the ground pin to charge the primary and that +12v
>input also feeds the secondary which grounds through the plug and
>mounting point. The signal for the transistor comes from the ECU through
>pin 1 on the M3 coil. What do you reckon?
>
>I'm thinking in my case I'd need a ECU with proper transistors to
>control that ground signal for the primary coil.
>
>Really sorry about asking these questions directly, but thought I'd ask
>someone who probably had his hands on COP coils. I have asked the
>diy-efi list, but have had zero feedback.
>
>Do the coils I describe make any sense? There seem like COP versions of
>general coils, except that a +12V feed has been given 2 separate entry
>points.
>
>Once again, sorry for such nonsense, confused questions. Feel free to
>ignore these if they're oddballs. :)
>
>Thanks.
>
>Gerard.
>
>

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