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

[Jhullmoto]

Hi folks, long time user, first time poster etc etc.
please let me know kindly if I miss step.

I’m a professional custom builder but this is only my second K Bike.

I have run the relevent searches but can’t find an answer. My questions are quite specific as I’ve been troubleshooting for a week now and I need to get this bike out to my client.

I’m currently rebuilding a 1992 K100RS 4v (abs no cat version.)
I have deleted the entire frame loom and replaced it with a motogadget M-Unit Blue system. This all works great (it’s not my first) However, I have kept the engine loom stock.

I have deleted the ABS as I’ve done a K1200/S100RR wheel and front end conversion.
I have deleted the side stand switch
I have deleted the clutch switch
I have a included the fuel pump relay & the fan relay

The bike was ridden into the workshop before disassembly and ran well. However, I have extensively troublshooted the obvious parts/systems when dealing with a no spark issue. The wiring, voltages, resistances all check out on the coils.

The problem:  After the rebuild I find myself with no spark on both coils. The fuel pump primes for 2 seconds at ignition on but does not come on during startup.

So my question is regarding the Motronic:
I have power going to pin 33 and 15. As I said, it sends the signal to prime the pump so it’s doing that bit right but it seems to be blocking proper startup procedures.

Does the Motronic, for security/safety reasons, block the startup procedure by restricting ignition and fuel?

I read that the H2o Sensor can send bad/no signal and that can cause this issue. Is that true? The one in the bike is not showing any resistance so I’ve ordered a new one but I could do with confirmation that that could be the problem.

If not, is there any other reason that the Motronic might block startup like this?

As I’ve said, I’ve run through the bike from battery to plug ends, I have continuity on all earths and the coils check out for resistance and voltages. (Besides, it’s both coils which suggests that it’s not the coils or the hall sensor. They wouldn’t usually go down on both sides at the same time.)

Any thoughts would be much appreciated.
I’ve about used up my own knowledge on this and a few other peoples to boot. I don’t want to start shotgunning parts at it (I prefer to hunt with a rifle) but I have swapped out the ignition amp (as I saw this was the issue in another thread) to no avail and the co pot (just because I had a spare in stock)

Thank you.

Jonathan

[frankenduck]

How did you delete the side stand switch? Did you short the GRN/RED and GRN/YEL wires to each other?

[Laitch]

Welcome, Jonathan.

From what have you been reading that you can't believe and why have you been reading it?  From what I've read, if there is no Hall Sensor sign input to the Motronic—or the Motronic can't process it—there will be neither fuel pressure nor spark. I believe that. Of course, it's easy for me to believe that because I'm not sweating bullets trying to start a K1100.


Have you been consulting the Motronic 2.1 & 2.2 Training Reference Book available in our Service Bulletins~Brochures section? A diagram from it is attached. According to the diagram, there should be an output signal at pin 12 when cranking.

[Jhullmoto]

How did you delete the side stand switch? Did you short the GRN/RED and GRN/YEL wires to each other?

No, I removed it from the equation in its entirety and replaced its feed on the fuel pump relay (pin 86) with a 12v (ignition on) As I understand it, it has nothing to do with the Motronic.

[Jhullmoto]

Welcome, Jonathan.

From what have you been reading that you can't believe and why have you been reading it?  From what I've read, if there is no Hall Sensor sign input to the Motronic—or the Motronic can't process it—there will be neither fuel pressure nor spark. I believe that. Of course, it's easy for me to believe that because I'm not sweating bullets trying to start a K1100.

Hi, thanks for your reply but I don’t understand what you are saying here. It was either this forum or the another K100 forum that suggested the H2O sensor as a possible culprit. As it’s just one of only two sensors that feeds directly into the Motronic,  I had just hoped to rule that out here. What I read might well be rubbish of-course and that’s exactly why I asked. It stated that a broken sensor could continuously report Hot and stop the startup procedure.

Thank you for your suggestion regarding the Hall Sensor to the ignition amp. I’ll check that asap and report back.

Thanks.

[Jhullmoto]

Welcome, Jonathan.

Have you been consulting the Motronic 2.1 & 2.2 Training Reference Book available in our Service Bulletins~Brochures section? A diagram from it is attached. According to the diagram, there should be an output signal at pin 12 when cranking.

Thank you very much for the manual! That’s very helpful indeed!

[Jhullmoto]

After reading the manual from Laitch (thanks, that’s an awesome resource) I have got a very small output on both the 2 motronic outputs to the ignition amp. Only a fluctuating 0.20v on both during cranking. One is black (sw) on pin 2 of the amp connector and one is black/white (sw/ws) on pin 7 of the amp connector. The manual states that it’s a low voltage but does not say the exact expected parameters.

I am picking up a replacement hall sensor today just in case that’s the problem. I’ll keep you updated.

I should quickly add a side note; this is the 2.1 motronic and as such (I think) has no CO sensor. There is a lot of discussion regarding the Co sensor but there was visibly no sign of one on the bike’s exhaust system nor is there a connector for it on the engine loom. I think I’m right in thinking that the 2.1 doesn’t utilise this and has only the potentiometer. The manual seems to confirm this in a roundabout way but confirmation would be good.

Also, and I’m just shooting from the hip here but the only wire out of the engine loom I haven’t resolved is the brown/white (br/ws) from the diag plug to the deleted abs control unit. Does this perhaps need a resolution? This is the only abs related wire coming from the engine loom.

Thanks again.

[Laitch]

Are you using the Motronic Diagnosis data at this link? There are several No Spark checks and a couple of Hall Sensor checks. They involve BMW's proprietary tester but most tests can be reproduced with a good quality multimeter. It's probably best to ignore involvement with ABS wiring right now. One point about the ingnition amp is that its contact surfaces must be cleaned and then covered with a thin layer of heat shrink paste so they make full contact with each other.  Attached is one of the No Spark resistance tests from the manual.
 
Does your Brick still have functioning diagnostic plug that you have tried to use?

Maybe Scott_ will chime in here with some observations.

[Jhullmoto]

Hi, thanks for replying. I’m just fitting up the replacement hall sensor now. Yes to the ignition amp question. It’s all correctly seated with paste on an earth strapped location to a clean metal surface. I have continuity checked the earths at all stages of the amp, heat sink and mounting plate but not measured the exact resistance. I’ll do that this evening.

Thanks for the diagnosis data. The diag plug is in the loom still minus the connected abs lead of course. However, sadly, I do not possess a fault reader for these bikes or indeed a bmw multi tester.

I don’t usually have to deal with fuel injection and ecu controlled motorcycles. This only my second k bike. Normally, I’m a classic Honda guy! :D Moving forward, I’ll get properly kitted out but for now, it’s just a multimeter I guess.

I’ll take all your suggestions on board and let you know when I have a little more data to share.

Thanks Laitch, you’re a star for helping me out mate! Glad I chose to join the forum!

[Laitch]

Thanks Laitch, you’re a star for helping me out mate! Glad I chose to join the forum!

It's too early to start the party, Jonathon, but I would like to find lime and coconut frosting on the vanilla cake when it's delivered.   Wait until you meet some folks here who actually own a K1100. Glad won't come close to describing that feeling. 

[Laitch]

Incidentally, you don't need a code reader, you can use a test light. Try following the methods described in this post.

[Jhullmoto]

Ha ha! No problem. It’s a K100RS though mate. Not a K1100 you’ve done that a couple of times and I just wanted to point it out so we’re not at crossed purposes.

[Laitch]

Ha ha! No problem. It’s a K100RS though mate. Not a K1100 you’ve done that a couple of times.

Inflation—it's affecting everything over here. Nevertheless, it should work with the Motronic 2.1 you've got. Try it; you'll be glad you did, maybe.

[frankenduck]

Incidentally, you don't need a code reader, you can use a test light. Try following the methods described in this post.

The "test light" needs to be a single low power 12V LED. The diagnostic plug does not put out very much power so if you try something like a multi-LED 1156 turn signal bulb it probably won't illuminate.

[Jhullmoto]

The "test light" needs to be a single low power 12V LED. The diagnostic plug does not put out very much power so if you try something like a multi-LED 1156 turn signal bulb it probably won't illuminate.

Hi, and thanks, In the article, when making a test lamp, it says to connect the positive side of the rig to battery + and negative to the diag plug? That implies that the diag plug connectors are switched earths (makes sense as they are all brown with a stripe) and as such any 12v led work. However, before I put a clean 12v straight down those pins, I’d like confirmation on that. If I damage the moronic, I’m screwed.

[Jhullmoto]

Hi, and thanks, In the article, when making a test lamp, it says to connect the positive side of the rig to battery + and negative to the diag plug? That implies that the diag plug connectors are switched earths (makes sense as they are all brown with a stripe) and as such any 12v led work. However, before I put a clean 12v straight down those pins, I’d like confirmation on that. If I damage the moronic, I’m screwed.

This is the part that worries me:
Motronic Fault Code Readout:
Connect a common 12V LED (One acceptable LED is a Radio Shack Red LED P/N 276-270)
to pin #1 (+lead to Battery + , -lead to Pin#1). The LED is not necessary for K-bikes…


I’ve popped the voltage meter on the diag plug outs. I’m getting 4v out the green/brown and 2 to 3v out of the brown/blacks.

[Jhullmoto]

Just to update you guys. Aside from now being very well read. (Thanks guys)
I’ve swapped out the H2O sensor this morning. Not a quick job. I’ve fitted up the replacement Hall Sensor but I noticed the  contacts on the engine loom side are in bad shape. It looks to me like it’s been minus its rubber protector sleeve for some time during its life. So, I have some new crimped female terminals arriving tomorrow and I’ll be replacing all five in the stock connector housing.

When all that’s done, I’ll probably go for another crank with the changes I’ve made and if there’s no significant improvement, I’ll go down the suggested fault code road. (I’ll still need answers to the above question though if and when I get there).

Cheers!

[Laitch]

. . .  Aside from now being very well read.
I’ve swapped out the H2O sensor this morning. I’ve fitted up the replacement Hall Sensor but I noticed the  contacts on the engine loom side are in bad shape. It looks to me like it’s been minus its rubber protector sleeve for some time during its life.
. . . The LED is not necessary for K-bikes…

The Motronic manuals wouldn't seem to make good summer reading at the beach (or whichever hopefully sunny recreational venue is handy where you are), so this is a good time to review them.

Please post a photo of the loom-side connection protective sleeve in its present degraded condition, and also a photo of the sensor-side connector.

Many blokes—to use a quaint word over here —with Motronic Bricks have used those code-reading techniques successfully. Your use will need to be a leap of faith based on anecdotal evidence provided by disembodied, mysterious posting on the Internet.  Some owners have read flashes from an LED, and others may have read flashes from the coolant temperature light in the instrument cluster as indicated in the omitted part of the sentence you quoted. Which method was used could have been a matter of convenience, or perhaps because the coolant temperature light didn't respond predictably or at all.

[sooprvylyn]

I posted a wiring diagram for m-unit to 4v bike on the wiring diagrams forum. Take a look at it, its pretty simple.

I did all the same deletes you have described on my k1000rs...which should be similar to yours.  No problems getting the bike to run using that diagram.

[Jhullmoto]

I posted a wiring diagram for m-unit to 4v bike on the wiring diagrams forum. Take a look at it, its pretty simple.

I did all the same deletes you have described on my k1000rs...which should be similar to yours.  No problems getting the bike to run using that diagram.

Hi and thank you. Yes I have seen that. You have done it much the same as me. I used my friend Tim’s diagram from Powerbrick for both my K-Bike builds. The only thing the munit really does (as far as ignition is concerned) is send a 12v to the coils & the starter relay. That side is working fine. The trick is knowing how to setup the relays etc. However, I’m pretty sure my problem is down to the engine loom, its components and how the motronic is responding to that. While troubleshooting, I have removed the munit from the equation entirely and I still have the same issue. I’ll have a good look at your diagram and see if there is anything glaringly different. I know Powerbrick run their fan direct from auxiliary 1 and delete the relay in favour of the fan being on all the time the engine is running but I’m not comfortable with that so I have included a relay as you have.

Thanks for sharing that mate. I’ll let you know if I spot anything.

[Jhullmoto]

Please post a photo of the loom-side connection protective sleeve in its present degraded condition, and also a photo of the sensor-side connector.

They are just dirty and corroded mate. Nothing unusual like a short etc. just 30 years old. The plug (loom side) has clearly been left uncovered that’s all. It has a split in it at the cable end. I just want to make sure I have good, clean connections. Don’t worry, I have all the right tools. It won’t be a bodge job and I’ll be using the original terminal housing. That’s in great shape. The terminals on the moulded cover on the replacement Hall Sensor look fine. I probably don’t need to do this, it’s just a peace of mind thing.

[frankenduck]

Hi, and thanks, In the article, when making a test lamp, it says to connect the positive side of the rig to battery + and negative to the diag plug? That implies that the diag plug connectors are switched earths (makes sense as they are all brown with a stripe) and as such any 12v led work. However, before I put a clean 12v straight down those pins, I’d like confirmation on that. If I damage the moronic, I’m screwed.

That's not how a diode works. It's not the same as using a piece of wire which would cause a short.

LEDs illuminate when there is a difference in voltage potential (a.k.a. volts) between the terminals.

For example, if you hook up 12V LED to a 12V battery the battery's anode (negative terminal) remains at 0V and the battery's cathode (positive terminal) remains at 12V.

Also note that LEDs are often polarized.

On a simple 5mm LED the slightly longer wire is the positive wire.

[Ingo]

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.

[Jhullmoto]

That's not how a diode works. It's not the same as using a piece of wire which would cause a short.

LEDs illuminate when there is a difference in voltage potential (a.k.a. volts) between the terminals.

For example, if you hook up 12V LED to a 12V battery the battery's anode (negative terminal) remains at 0V and the battery's cathode (positive terminal) remains at 12V.

Also note that LEDs are often polarized.

On a simple 5mm LED the slightly longer wire is the positive wire.

Perfect. Thank you!

[Jhullmoto]

Sorry for the double post. These old forum templates are hell on an iPhone.