TRACK DAY BMW E30 rev counter problem

[Bryan the pilot]

I am rebuilding a track day E3O which had a M52B28 conversion ,the rev counter installed was a RMD brand which worked fine but I had to dismantle most of the wiring as the car had no dashboard at all just a alloy switch panel , of course after getting everything else working again in the replacement dash I cannot get the rev taco to work , I have scoured the net but no luck , I did see one post that you take the signal off a "blue " wire in the ECU but mine has no solid blue ?? , I was also told the black wire but after trying the 3 black I can find , nothing ?? I also tried taking off the crank sensor connection I first tried the black , nothing , then the red , which gave some intermittent reading on the gauge and caused it to swing full scale when I turned the engine off ??
the Wiring instructions that I got off the web are here
https://www.caigauge.com/documents//pdfs/pil019-367.pdf
Perhaps someone will be kind enough to advise me further ??
thanks in advance
Bryan

 

[plugsandsparks]

What ecu are you running ?
Is the engine individual coil on plug ?

 

[brianmoooore]

If you're using a MS41 ECU, then the engine speed output signal should be on a plain black wire from pin 36, according to the circuit diagram I have. If the 20 pin diagnostic socket is still present, it's connected to pin 1 of that.
It's a plain black wire in every BMW DME loom that I'm familiar with.
Plain blue is a road speed signal in some BMWs.

 

[Bryan the pilot]

What ecu are you running ?
Is the engine individual coil on plug ?

Hello
thanks for your reply , it is a individual coil on plug 6 cylinder using a E36 ECU

 

[Bryan the pilot]

If you're using a MS41 ECU, then the engine speed output signal should be on a plain black wire from pin 36, according to the circuit diagram I have. If the 20 pin diagnostic socket is still present, it's connected to pin 1 of that.
It's a plain black wire in every BMW DME loom that I'm familiar with.
Plain blue is a road speed signal in some BMWs.

hello Brian , thanks for replying , I have the same wiring diagram and I have tried every black wire including pin 36 , no joy , and also tried the diagnostic socket pin one also .

 

[plugsandsparks]

Hello
thanks for your reply , it is a individual coil on plug 6 cylinder using a E36 ECU

Its not obvious from the wiring diagram is it the MS41.0 ECU. It shows a tacho signal at the diagnostic plug and one towards the instrument cluster, but how that signal is derived and whether your tacho can decode it correctly will be the issue. Its easy to derive a tacho single from a coil pack but as you have coil on plug you will only get one signal per 2 revs so will read alot slower than correct.
Heres the link to the diagrams

Download BMW ETM E36 circuit diagrams

 

[brianmoooore]

If it's a MS41, then that's the engine speed signal on pin 36, so either it isn't getting to the tacho, or your tacho isn't reading it.
The signal gets split to several places in the loom, so check it isn't being shorted out somewhere, and I know from experience that it's susceptible to poor connections along the way, so check any joints an plugs/sockets.
According to the instructions for your tacho, it should be compatible. DIP switch 5 should be on and DIP 4 off, but try it on if off doesn't work.

 

[Bryan the pilot]

If it's a MS41, then that's the engine speed signal on pin 36, so either it isn't getting to the tacho, or your tacho isn't reading it.
The signal gets split to several places in the loom, so check it isn't being shorted out somewhere, and I know from experience that it's susceptible to poor connections along the way, so check any joints an plugs/sockets.
According to the instructions for your tacho, it should be compatible. DIP switch 5 should be on and DIP 4 off, but try it on if off doesn't work.

Hello Brian
thank you for your reply
ok perhaps I did not explain correctly , the rev counter is a stand alone type so not into the loom , cable directly from the ignition live , neg earth (body) and then to ecu ,it was as I said working fine before and I have not moved any of the "dip" positions I attach a pic of the ecu in the hope it might help ?, However using a multimeter 0 to 600 range I get no reading off pin 36??

 

[brianmoooore]

Had a 5 series M52B28 in the workshop this morning for tyre pressure checking, so while it was there I popped the bonnet and connected my DMM to pin 1 of the diagnostic. This has the MS42 ECU, which is near enough the same as the MS41, but with a control output for the second vanos.
DC volts produced no meaningful reading.
AC volts produced a reading of just over 1 volt, which increased only very slightly as the revs increased.
DMM has a frequency setting, which produced sensible results.. About 33 Hz at idle,, which increased with revs steadily. Read 100 Hz at 2000RPM.

 

[Bryan the pilot]

Had a 5 series M52B28 in the workshop this morning for tyre pressure checking, so while it was there I popped the bonnet and connected my DMM to pin 1 of the diagnostic. This has the MS42 ECU, which is near enough the same as the MS41, but with a control output for the second vanos.
DC volts produced no meaningful reading.
AC volts produced a reading of just over 1 volt, which increased only very slightly as the revs increased.
DMM has a frequency setting, which produced sensible results.. About 33 Hz at idle,, which increased with revs steadily. Read 100 Hz at 2000RPM.

Hi thanks for that ,I do appreciate your replys and help and to be honest and not being skilled (or anything ) in this field I am at a bit of a loss , i have another stand alone rev counter which I got to try in case mine was broken but it gets nothing off pin one on the diagnostic or 36 on the ecu ???
mystery ??