1992 K100RS 4v abs (no cat) No spark or fuel feed after rebuild. [SOLVED]

[frankenduck]

Don't forget a resistor in line with the LED. LED's run of 1.2 - 1.5 V DC, 12 Volts is going to blow the LED.
 I've wired 2 LED's in anti-parallel with a in line resistor, lights up whenever there's 12 V present, no matter the polarity.

You don't need a resistor if you buy a 12V LED.

For example, I use 12V 3mm LEDs to backlight my dash switches. No resistor needed.



You can also buy pre-wired LEDs that already have the resistor wired in.
https://www.amazon.com/dp/B01EFHRF0Q/

[Jhullmoto]

Perfect. Thank you!

Thank you but to be honest and with respect to all of course, this all seems way too ‘bodge’ for me risk on a clients bike and I don’t work like that.  There’s a lot of money at stake here and trying to source a replacement motronic would be a time and expense issue I just can’t afford. If it were my personal ride, I’d have a go… sure but I think for this bike, in the absence of the right diagnostic equipment, I’ll have to continue down the traditional troubleshooting route.

Thank you both kindly for your advice regarding the test rig. If all else fails, I may come back to it.

[frankenduck]

I recommend doing the fault code read. As Mick points out, you don't even need the LED on a K because the temp in the cluster light will flash the code.

I just compared the wiring diagrams and the pins are the same color codes for a K100RS4V and Mick's 93 K1100 and go to the exact same places.

Pin 1 BRN/BLK wires goes to Motronic Pin 20 and the temp light
Pin 2 BRN/WHT to ABS Pin 23
Pin 3 BRN/GRN to Motronic Pin 12

All you need to do is ground Pin 1 for 5 seconds to get the Motronic in fault code mode.

[Jhullmoto]

Thank you Frankenduck. Yes, that makes sense, I’ll see if the Motoscope pro deals with that in the same way as the stock K100 dash.

I should have something else to report later this afternoon regarding the replacement Hall Sensor, its new connection and the Temp sensor.

I do have one more ‘niggle’ regarding the ignition amp. I have covered all the recommendations regarding its installation. It’s clean, mounted on its stock aluminium heat sink (with paste) on a bare metal plate that includes an earth strap. All earth continuity is confirmed. However, I notice that, on the stock bike, the amp’s heat sink is mounted to an aluminium mounting surface that is attached around the battery compartment. The one I’ve fabricated is made of Mild steel and doubles as a coil cover.  I can of course knock up a quick Aluminium mount to test this but is it possible that the secondary mounting materiel have an effect on its operation? I think I’m just clutching at straws here. Im starting to question all my decisions.

In the image, though you can’t tell, the underside of the aluminium heat sink is bare metal.

[Jhullmoto]

Forget the ignition amp question above.

PROBLEM SOLVED!

The Hall Sensor was the issue. Either the sensor itself or its connector. Can’t be 100%.
After being pointed in the right direction by you guys and detailed reading of the M2.1 Motronic and the Diagnostics documents, I was able to confirm that my wiring was indeed correct and in fact, it was the Motronic that could not correctly process the signal from the Hall Sensor. This could have been because (when cleaning it up for the rebuild) I accidentally damaged it, or because the connection plug had seen some corrosion. So I swapped out the hall sensor itself and on the loom side, I replaced all 5 female pin terminals inside the stock connector housing.

It is now, not only supplying a beautiful clean spark, the fuel pump feed is now operating correctly too.

A good friend of mine and ex Dakar moto mechanic always says: (and I said this earlier in the thread) “When troubleshooting, Always hunt with a rifle, never a shotgun.” You guys helped me do just that. Thank you to everyone for your help, especially Laitch and Frankenduck.

If anyone is in or near London at the end of the month, the bike and I are at the Bike Shed London Show 2024 in the pro category, or hit me up on instagram (just search jhullmoto)

Thanks again,

Jonathan

[Laitch]

Thanks for the followup, Jonathan. Please post profile photos of the completed project in this thread. Good luck!

[frankenduck]

“When troubleshooting, Always hunt with a rifle, never a shotgun.”

You don't have to use shot in in a shotgun, you can use a 12ga slug.

Ignition amp: Heat is the enemy with that component so that wouldn't impact performance at startup on a cold bike. If the bike starts fine but then runs like crap after several minutes then that is the usual symptom of an overheating ignition amp. But it sounds like you have it mounted well with heat sink compound so you should be OK on that front.

[Jhullmoto]

Hey folks. As promised:
Here’s the bike.
1992 K100RS 4v
K1200 wheel conversion
YSS Sidewinder rear shock conversion
S100RR front end conversion
Centre post subframe conversion
Colour: BMW Hockenhiem Silver
M-unit Blue electrical system
Antigravity 801 powered
DNA Air filter conversion

[Laitch]