Author Topic: Installing digi tach/speedo..pulse generator?  (Read 815 times)

Offline RG68RG

  • Posts: 25
  • I Love YaBB 2!
Installing digi tach/speedo..pulse generator?
« on: September 29, 2018, 11:54:42 AM »
I'm attempting to install this digital tach/spedometer and I've been instructed to attach the tach wire to the "pulse generator"?  Anyone know where the pulse generator is on this bike, and where is it?? I'm confused I assumed the two green striped wires that come up beside the coil on top of the motor.. but am not sure.. 

Offline RG68RG

  • Posts: 25
  • I Love YaBB 2!
Re: Installing digi tach/speedo..pulse generator?
« Reply #1 on: September 29, 2018, 02:17:32 PM »
Okay, I think I may have found it. Hall Impulse transmitter..Now to find it.

Offline Tony Smith

  • Posts: 2274
  • Graduate, Wallace and Gromit School of Engineering
Re: Installing digi tach/speedo..pulse generator?
« Reply #2 on: September 29, 2018, 04:54:42 PM »
Do not connect anything to the hall effect trigger wiring, the hall effect device is running pretty much at its design limit providing a signal to the Ignition Control Unit.

Now, the ICU actually does have a Tach output pin, but this is not used by the BMW wiring harness. I suppose theoretically you could pick up the signal there if in fact your tach is capable of using it.

The more normal point to obtain a tach signal is the positive power lead to the coils, which is where you may have a problem.

The BMW ignition system (in common with many motorcycle systems) fires a waste spark during the exhaust stroke, the problem this creates is that this signal will be sent to the tach ad result in it reading exactly twice the revs the engine is actually doing.

Most tachs have the facility to work with 1,2,4,6,8 cylinders, usually by way of a switch. Simply change that switch setting until you get the correct figure.

If your tach does not have such a switch, well you are in a world of hurt. BTW picking up the Tach pin on the ICU won't help because it is still generating twice as many pulses as are actually required.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |

Offline RG68RG

  • Posts: 25
  • I Love YaBB 2!
Re: Installing digi tach/speedo..pulse generator?
« Reply #3 on: September 29, 2018, 05:06:43 PM »
Quote
Do not connect anything to the hall effect trigger wiring, the hall effect device is running pretty much at its design limit providing a signal to the Ignition Control Unit.

Now, the ICU actually does have a Tach output pin, but this is not used by the BMW wiring harness. I suppose theoretically you could pick up the signal there if in fact your tach is capable of using it.

The more normal point to obtain a tach signal is the positive power lead to the coils, which is where you may have a problem.

The BMW ignition system (in common with many motorcycle systems) fires a waste spark during the exhaust stroke, the problem this creates is that this signal will be sent to the tach ad result in it reading exactly twice the revs the engine is actually doing.

Most tachs have the facility to work with 1,2,4,6,8 cylinders, usually by way of a switch. Simply change that switch setting until you get the correct figure.

If your tach does not have such a switch, well you are in a world of hurt. BTW picking up the Tach pin on the ICU won't help because it is still generating twice as many pulses as are actually required.
The tach does have 1-4 cylinder input. Right now I had it set to 2 cylinder. I can try to move it back to 1 cylinder if that will tell it half the revs? Also..not sure where the tach pin is, much less the ICU....also not sure which wire is the positive power lead to the coil.. I see two black ones that appear to be grounded to the coil..   Unless this the ICU? and ICM? is the same thing? If so i found it bolted with two bolts to the frame under the tank. BTW.. My tach was already reading twice the revs as it had which is one of the many reasons i had to replace everything... go figure.. as of now.. I have never seen the tach move other than to sweep at power up..  
« Last Edit: September 29, 2018, 05:35:23 PM by RG68RG »

Offline RG68RG

  • Posts: 25
  • I Love YaBB 2!
Re: Installing digi tach/speedo..pulse generator?
« Reply #4 on: September 29, 2018, 05:43:05 PM »
Just a thought.. it is still possible that the tach on this unit is broken (except that it does sweep on power up) other than that not seeing any movement at all.. even wrapping plug wires, original gauge signal.. nothing..

Offline RG68RG

  • Posts: 25
  • I Love YaBB 2!
Re: Installing digi tach/speedo..pulse generator?
« Reply #5 on: October 01, 2018, 10:24:02 AM »
Anyone know which (Unused) pin on the ICU can be used for the tach? I have the replacement tach coming today and want to try that signal...
« Last Edit: October 01, 2018, 10:24:46 AM by RG68RG »

Offline Tony Smith

  • Posts: 2274
  • Graduate, Wallace and Gromit School of Engineering
Re: Installing digi tach/speedo..pulse generator?
« Reply #6 on: October 01, 2018, 03:07:36 PM »
Quote
Anyone know which (Unused) pin on the ICU can be used for the tach? I have the replacement tach coming today and want to try that signal...

Pin 7 - if you have an OEM wiring harness there is currently nothing connected to Pin 7.

BUT - Not all OEM BMW marked ICUs implement Pin 7, nor do a number of copiers. However I can  state categorically that the ORIGINAL fitted ICU to all bikes 1981 through 1984 does implement Pin 7. Copies manufactured by (amongst others) Werle, Siemens and a large number of nameless European and Chinese manufacturers might, or might not.

It gets worse. the "grandfather" of all these devices is the Bosch 0 227 100 124 (which will work perfectly in our BMWs by the way). But the same unit manufactured by Bosch USA does not implement pin 7.

Late model "high power" ICUs (own irremovable heat sink and "slanted" mount) - I don't know.

I have a selection of BMW, Bosch, European copies, Chinese copies and unknown origin copies (Endurolast). To date I have spent time working out the timing differences between them and why that might be so, I have never spent any time working out which ones fully implement the tach pin.

Given that nobody I know of has ever had to use the tach pin on the ICU to get a signal for their aftermarket tachometer, and given the fun and games you will have just to access that pin (and the easiest way I can think of is to find  a European car wreck that used the same module and cut the connector out of the wiring harness and then fabricate a "remover" to extract one of the sockets which you then place in your BMW ICU socket) I would say find a better tachometer, or at least one from your current manufacturer that isn't faulty.
1978 R100RS| 1981 R100RS (JPS) | 1984 R65 | 1992 KLE500 | 2002 R1150GSA |