M50 coil connector pinout?

[ArtemLepilov]

I need an 1991 M50 harness coil connector pinout.. Does anyone know what the signal should be for it?

-Artem

[Jon K]

It's in the bentley.

[ArtemLepilov]

I saw it (the bentley pinout), but it would help to know what I would need to expect to see from it... upon analysis, like - i checked the potential difference on the side connector and it was around 10V on some and 6V on others, also I couldnt get anything out of the middle connector, even when cranking. The ground of the multimeter was on the car ground and the other pin was on the middle connector. Interesting thing - the potential difference between the commom car ground and the positive lead on the coil connector was around 12V I am guessing - the multimeter was old and analog, it went off the chart. But when connecter to the opposite pin on the connector it was around 6-10V as i mentioned. Can anyone make any sense of this?

-Artem

[jjw]

You should never use analog meter on computer controled cars. Must have a high impedence DVOM or scope to prevent frying the computer.

[ArtemLepilov]

Alright, well I checked it with a digital one, in any case and I had no idea what to look for. Coils are good, there is still no spark and over 200 miles on the odometer since the cylinder was malfunctioning.

Does anyone in the boston/worcester/MA area has a 1991/1992 BMW E34 with an M50 engine who would let me borrow their ECU for a bit?

-Artem

[Rustam]

I saw it (the bentley pinout), but it would help to know what I would need to expect to see from it... upon analysis, like - i checked the potential difference on the side connector and it was around 10V on some and 6V on others, also I couldnt get anything out of the middle connector, even when cranking. The ground of the multimeter was on the car ground and the other pin was on the middle connector. Interesting thing - the potential difference between the commom car ground and the positive lead on the coil connector was around 12V I am guessing - the multimeter was old and analog, it went off the chart. But when connecter to the opposite pin on the connector it was around 6-10V as i mentioned. Can anyone make any sense of this?

-Artem

When you say middle connector do you mean middle as seen on the schematic or as seen on the actual plug/socket? Per Bentley's schematic middle connector and right connector should be connected to multimeter leads to check for current.

And then - how sensitive is your multimeter? If its not sensitive enough to see a pulse you will not see difference. And besides - did you make sure that you switched the multimeter to "AC" voltage? The ECU sends pulses to activate coils when each has to fire - that's alternate current...

I would check each left connector of coils for continuity with car's ground. I would also check each right connector for continuity with pin 56 of the ECU. I would finally check for continuity from each middle connector to respective pin of the ECU. All directions as seen on Bentley's manual schematic.

[ArtemLepilov]

Yea, I noticed that the pinout and the actual is different. I checked the resistances and everything throughout - I went all the way to pin (50 I think) from the right side connector and the resistance came up as zero, so I am assuming that the wiring is good. The only thing that is left is the ECU and the coil... and the coils are good, im sure of it. I tried many of them and a lot of them were on the car before, in the working cylinders.

Any other ideas? I am really tired of this and a new motronic system at a dealer costs over $1000!!

-Artem

[Rustam]

Yea, I noticed that the pinout and the actual is different. I checked the resistances and everything throughout - I went all the way to pin (50 I think) from the right side connector and the resistance came up as zero, so I am assuming that the wiring is good. The only thing that is left is the ECU and the coil... and the coils are good, im sure of it. I tried many of them and a lot of them were on the car before, in the working cylinders.

Any other ideas? I am really tired of this and a new motronic system at a dealer costs over $1000!!

-Artem

check your email for motronic 3.1 schematic

[ArtemLepilov]

Got the unit out.. checked resistors... they were fine. I know that it could also be the transistors. How would I test those?

-Artem

[Rustam]

Got the unit out.. checked resistors... they were fine. I know that it could also be the transistors. How would I test those?

-Artem

How did you check the resistors? Did you unsolder each one and measure resistances? If not - then you checked them while on the circuit - then those resistances are of everything that comes along the way between the multimeter leads - more than just the resistors.

If the resistor is good - unsolder the transistor controlling coil #4, buy a new one, solder in and see if things work. The transistor is very likely the culprit since the chips do work - we know that they work because other coils provide the spark.

You can ask for transistors by talking to a sales representative from digikey.com - they have very extensive catalog.

[ArtemLepilov]

Sounds great, I will check the wiring over again on friday extensively. If the ECU is the culprit, I will try to repair the transistor, if that doesnt work I may consider going MS - I dont need an original ECU if im doing MS, or do I?

-Artem

[Rustam]

Sounds great, I will check the wiring over again on friday extensively. If the ECU is the culprit, I will try to repair the transistor, if that doesnt work I may consider going MS - I dont need an original ECU if im doing MS, or do I?

-Artem

You have to make sure that you check the wiring to the point of being certain that original problem that killed the transistor was not initiated by a short circuit of any type - whether buying new ECU (I hope not) or simply a transistor - that problem must not be there again.

Now what is "MS"???
And I guess you did unsolder the resistors to check them?

[ArtemLepilov]

Megasquirt. I wouldnt buy a new ECU anyway. I wish I could get one to test it soon, but I guess it will just come to me testing the wiring thoroughly.

I didnt unsolder the resistors to test them. I will do that upon a thorough check of the system on friday.

-Artem

[Rustam]

Megasquirt. I wouldnt buy a new ECU anyway. I wish I could get one to test it soon, but I guess it will just come to me testing the wiring thoroughly.

I didnt unsolder the resistors to test them. I will do that upon a thorough check of the system on friday.

-Artem

yes you must unsolder them - otherwise you get the resistance of them and everything else that comes along for the ride. Only remove the resistor that controls coil 4 - no sense undoing those that are obviously fine - you may make things worse working more than you have to.

I'll be waiting for your update.

[ArtemLepilov]

I should check for all that friday. Thats where I will throw the car in the garage and will have some time to work on it.

-Artem