Does the Hall sensor need to be connected in order to start the bike? Bit stumped here. When we press the starter we can hear the load shedding relay switching, but the starter relay doesn't. When the starter isn't pressed we have -4 V over the starter relay power wires, which changes to 0 V when we press the button. Wiring between the starter, ECU and ICU tested OK, but can't find out where the half power is coming from. I wonder if the ICU is the issue....

I'm trying to help Hutch here, but look like an ass :-)

Anybody, please help, thanks!

Rene (hfxrzw)

Yes. It provides the timing pulse for the ICU.

Thanks, I know what it does, but in order to start you need to get a signal to the starter relay whilst the bike isn't running yet (so the Hall sensors wouldn't work yet). Somehow the wire to the starter relay don't get enough volts/amps and normally I would expect to see 0 V with no starter button pushed and 12.X V (battery voltage) when pushed, so that 12 V would energize the starter relay coil and allow the battery power to reach the starter motor. However we have -4V with no action and 0 V when we press the starter.

I've measured the switches (clutch, starter and emergency stop) with work OK and the wires between the switches and the modules (ECU and ICU) are OK.

Bit stumped where that 4 V is coming from...

PS When the starter button is pressed the fuel pump relay switches....

@energyhutch wrote:Does the Hall sensor need to be connected in order to start the bike? Bit stumped here. When we press the starter we can hear the load shedding relay switching, but the starter relay doesn't. When the starter isn't pressed we have -4 V over the starter relay power wires, which changes to 0 V when we press the button. Wiring between the starter, ECU and ICU tested OK, but can't find out where the half power is coming from. I wonder if the ICU is the issue....

I'm trying to help Hutch here, but look like an ass :-)

Anybody, please help, thanks!

Rene (hfxrzw)

Before I will atempt to answer the question I will need to know what model bike it is. I presume it is a K100 8V.
You will notice that many put the model of bike they own in the signature line which saves you typing it repeatedly and others relying on an often failing memory.

The bike should turn over on the starter even if the hall sensors are disconnected but will not of course start.
When the starter button is pressed an earth is extended to the fuel injection relay for 1.5 seconds and by that time the engine should be turning and recieving signals from the hall sensors and will continue to extend that earth. That earth also lets the fuel pump relay operate making the pump run.
The load shedding relay can only release if the starter relay is sending 12v to the starter and that happens when the starter relay operates. For the moment dont even consider the operation of the load shedding relay as that will not stop the engine starting even if it does not release.
Check that when you press the start button you get 12v at the black/yellow wire at the start relay and that there is an earth connection on the brown wire in the same 2 pin plug. if you get that 12v and the relay clicks then check that you get 12v at the terminal on the starter motor. It should be no less than 10.5v
I suspect that there will be no 12v at the starter which will mean the starter relay is cactus and not contacting.
If you are getting a negative voltage reading you have the leads on the wrong way, this is not in any way a disaster using a digital meter but can be misleading.

Posts in other threads indicates energyhutch owns a 1985 K100, Rick.

Rob, you are correct :-)

Rick, fair dinkum :-). I should have been a bit more forthcoming with info. Bike's indeed a '85 K100

OK, if you bridge the switch contacts of the starter relay the starter motor is running, so in my view its a matter of the starter relay control wires (brown/red & yellow/black) not getting the 12V when the starter button is pushed. When you push the starter button the fuel pump relay switches, but that's it. Battery has good power, no worries there.

I'm not hung up on the + or - of the Voltage (appreciating your point), but the fact that there's only a difference of 4 Volts initially and no voltage difference between the two leads (brown/red & yellow/black) when the starter button is pressed is 'different' :-)

The loom has been worked on to install a different speedo (Acewell.), but even with those wires disconnected we have the same issue.

I did note there was no 'altitude plug' fitted nor was that socket fitted with a bridging wire, don't know if that would be required.

Strange thing is the 4V over the contacts when not engaging the starter button, I would expect 0V then, and 12V when you press the button.

Hutch already replaced the loom with another one, but got faced with the same issue. Full marks for the young man for hanging in there! :-)

Thanks for thinking with me!

Do you pull in and hold the clutch before you press the start button? (BTW this is required when you remove the OEM instrument cluster because the start enable circuit is part of the cluster).

Hi Rob, yes we did, aware of that.

Strangely enough something is switching (we go from 4V to 0V), but not enough power is switched. Strange one. I need to dig out my spare injection module and fit it/see what it does.

I think I've ruled out the switches and the wiring between them and the modules (ICE & ECU). Probably overlooking something simple....

OK, Hutch changed the injection brain and the bike is running now after some readjustments :-)