Pins on M50 coil? What does what? And what kind of signal over each?

[Jon K]

It is my understanding that Pin "1" is ground, Pin "15" is +12v, and pin "4a" is the trigger wire?

If this is true, while the car is on, does the coil always have GND and +12v? What kind of signal goes across the 4a pin? I cannot find it in any bentley manual, etc.

[Bill R.]

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It is my understanding that Pin "1" is ground, Pin "15" is +12v, and pin "4a" is the trigger wire?

If this is true, while the car is on, does the coil always have GND and +12v? What kind of signal goes across the 4a pin? I cannot find it in any bentley manual, etc.

[Bill R.]

help prevent any short circuits and to suppress high voltage being induced back into the primary winding. Pin 1 is the trigger to ground, pin 15 is the 12v and 4a is the ground on the secondary



It is my understanding that Pin "1" is ground, Pin "15" is +12v, and pin "4a" is the trigger wire?

If this is true, while the car is on, does the coil always have GND and +12v? What kind of signal goes across the 4a pin? I cannot find it in any bentley manual, etc.

[Jon K]

help prevent any short circuits and to suppress high voltage being induced back into the primary winding. Pin 1 is the trigger to ground, pin 15 is the 12v and 4a is the ground on the secondary

Bill if I am reading that properly, that means that the ECU pulses ground on pin 1?

The bentley shows:

Pin 1 (-) and Pin 15 (+) and I am getting a short basically, MS will not turn on when its like this and I get a spark at the + and - terminal on a car battery im testing on the bench.

So is that confirmed, the Pin 1 is the trigger and it is supposed to see pulses ground?

[Bill R.]

primary winding. In other words making and breaking the ground on the primary winding. One end of the primary is hot as you can see and the other end goes to ground through that transistor in the dme that switches on-off or triggers as you think of it. When that field is broken or not allowed to go to ground that induces the spark on the secondary winding and to the sparkplug.



Bill if I am reading that properly, that means that the ECU pulses ground on pin 1?

The bentley shows:

Pin 1 (-) and Pin 15 (+) and I am getting a short basically, MS will not turn on when its like this and I get a spark at the + and - terminal on a car battery im testing on the bench.

So is that confirmed, the Pin 1 is the trigger and it is supposed to see pulses ground?

[Jon K]

primary winding. In other words making and breaking the ground on the primary winding. One end of the primary is hot as you can see and the other end goes to ground through that transistor in the dme that switches on-off or triggers as you think of it. When that field is broken or not allowed to go to ground that induces the spark on the secondary winding and to the sparkplug.


So grounding Pin 1 means there is no spark... and when you let that ground off it then sparks? So kind of like the opposite of what you'd expect?

[Bill R.]

with points based systems much 30 years ago..;)




So grounding Pin 1 means there is no spark... and when you let that ground off it then sparks? So kind of like the opposite of what you'd expect?

[Jon K]

with points based systems much 30 years ago..;)



Haha ok - so now what youre saying is basically from my MS ecu, the igintion output has to be a pulsed ground that lifts to trigger. Hrm. Ok. Thanks very much Bill - also what software is that?

[pingu]

A difference between the M50 coil packs and the ignition coils of 30 years ago is that on the old ones, there was a single coil with an electrical tap partway along the coil winding - they're a type of transformer called an autotransformer.

In the M50 coil packs, there are two electrically separate coils that are magnetically coupled together. Pin 4a isn't there merely to help prevent short circuits and to suppress high voltage being induced back into the primary winding - it's the return path for the secondary coil and so is absolutely essential.

The diagram that Bill included unfortunately doesn't show the polarity with which the two coils are magnetically coupled and so there isn't enough information to definitively say which way pin 1 goes to make a spark (though from the diode in the coilpack, it is apparent that pin 4 goes -ve during a spark).

With the M50 coilpacks, a spark could conceivably be generated by pulling pin 1 to ground using the NPN transistor in the DME or by turning the transistor off and allowing pin 1 to float to +12V. These two alternatives are pretty much equivalent as far as the primary winding is concerned (which just needs to see a rate of change of primary current in order to generate voltage at the secondary).

With the information so far available, it's a bit 50/50 as to whether pin 1 goes to GND or +12V in order to fire the spark. My guess is that pin 1 goes to GND as, for geeky technical reasons to do with NPN transistors, it's usually easier to get an NPN transistor to turn on rapidly than to turn off rapidly. But it might be that pin 1 floats to +12V to make the spark!

A bit rambling but I think you need further information (do you have a circuit digram for the DME?) or maybe get an oscilloscope on pin 1.

[Jon K]

I wish I had an oscilloscope that'd make my life enjoyable. Theres a circuit for the DME in the back of the Bentley but it just has a pin out, not what type of voltage vector is present.

I have another pin out for the ecu harness and Pin 25 is ignition coil 1 primary signal . Tester display says: "Oscilloscope". Great. Anyone have an oscilloscope and an M50?

I trust you are right Bill, with the experience and all, are you positive about the ground thing - its not positive trigger is it?

[Bill R.]

bmw training manuals so i would imagine its correct. While i make no claims to be an electronics engineer this is how i interpret it to read. More info on the various dme's that bmw uses.




I wish I had an oscilloscope that'd make my life enjoyable. Theres a circuit for the DME in the back of the Bentley but it just has a pin out, not what type of voltage vector is present.

I have another pin out for the ecu harness and Pin 25 is ignition coil 1 primary signal . Tester display says: "Oscilloscope". Great. Anyone have an oscilloscope and an M50?

I trust you are right Bill, with the experience and all, are you positive about the ground thing - its not positive trigger is it?

[Jon K]

Awesome - thanks bill. It even says the length of time it is grounded is the dwell (charge) and then ECM interupts and the magnetic field fires to the secondary winding etc. Awesome.

[pingu]

These latest pictures settle it - the DME grounds pin 1 briefly (in order to build up the current in the primary) before the spark is required, then releases pin 1 (i.e. breaks the current path through the primary coil) to fire the spark.

[Rustam]

bmw training manuals so i would imagine its correct. While i make no claims to be an electronics engineer this is how i interpret it to read. More info on the various dme's that bmw uses.

Bill is correct regarding connection to ground through transistors. Motronic 3.1 schematic shows exactly same transistor application.