Riding home a few nights back on my '82 K100rs I had a total breakdown and cannot find the problem. The bike was running particularly well (of course) and then ignition totally dies while travelling at 60mph. Ignition lights and head lights remained on. Tried to restart but no cranking at all. Tried to bump start as on hill but no ignition (I presume).

AA arrived and we went through every connector we could find - no luck. Finally on low loader at 2:30 am. Engine will crank when battery applied direct to starter. Replaced the load shed relay as I had a problem last year with headlight remaining on and thought it may be connected. No fix.

Fuel relay clicks when pressing start button. Looked at wiring diagram and it looks like the starter solenoid is earthed through ignition module which makes me suspect the module has gone wrong - is this too simple thinking? Voltage at switch side of the solenoiud is only 9V? Curious. Fuel pump does not come on when turning on ignition.

So basically engine will not crank through Start switch and no ignition. Any suggestions on what to check next much appreciated

Chris
 p.s. The alternator light had glowed fairly brightly 10 miles previously, but had gone out.

If the fuel relay clicks when you press the start button and the fuel pump doesn't come on then suspect the pump first of all.
Remove it and test it on a battery and caution it will have fuel in it and connecting to a battery can cause sparks.
The pump on a K100 will start when you press the start button not when you turn the key.
Sometimes a bit of crud gets in the pump and jambs it try reversing the battery connections, If it runs when you reconnect the right way check to find how the crud got in. It's usually the strainer at the base of the pump has a split or tear.

How good is the battery? Its normal enough for the alternator light to come on at night, but its usually just a dim glow when you close throttle and use the brakes, it would possibly show a very dim glow on full beam but it would not normally glow brightly. If it was showing bright all of a sudden then there would seem to be a problem on that side of the electrics. First off check the battery, if its low remove it and charge it up and see if that works. If charging it solves the problem just make sure the battery is holding the charge then check that the alternator is producing current. If you have the bike running turn on the lights and rev it to 2000rpm, then turn lights off. The red light should not glow at this point. If your voltage is way off as in a dud battery the K wont go. This may not be the problem but start with the basics as they say.

I did think of the fuel pump too but I thought that if it failed the starter would still turn over.

Oops that'll teach me for not reading it properly.  
Try the starter relay by disconnecting the small 2 pin plug and apply 12 v and earth directly to those 2 pins and check the plug on the module and make sure all the connectors are working and that it is plugged in properly.

Rick

You may well be right because when the battery failed on my LT it still tried to turn over. There are a few earths to check too, like the gearbox lug and even the battery terminal connections.

Check out this thread too....

https://www.k100-forum.com/t7808-good-morning

Some similarities.....

The earth connections under the tank is where the ICU gets the earth for the starter relay.
Its on the left side about mid point and has many brown wires connected to the frame under a 6mm bolt. Give them a good clean.

Thanks lots for your advice. Gave earth connection undertank a quick loosen/tighten. I'll give it a good clean later.
I've been doing all my testing with tank off and fuel pump disconnected. I assume It should still crank if all system is in good order?

Chris

Yeah it will still crank over with the tank off

Tried cleaning earth onto frame below tank. Hey Presto, the engine cranked. Put tank back on then tried to start engine. Just a click, back to square one. Anyway must be getting closer, thanks for advice, chris

Check the connections in the 9 pin plug for the RHS switch block it sounds like a lose connection.  Also make sure that when you put the tank back on it doesn't squash the 9 pin plug as there is limited room under the tank and it easy to do.

done the 9 pin plug, no joy. Tried every earth and connector block. Tried earthing the brown/red wire to starter solenoid and engine cranks well - didn't have tank on and no engine firing. So solenoid is getting no earth from the ignition module. Module may have some overheating discolouration at the plug join - very slight maybe imagination or corrosion. Tried applying earth direct to module terminal in case wire had a break. I'm starting to suspect the ECU module but can't see why it cranked over yesterday a few times and don't understand if there is a logic in the module to supply earth when ignition on.
Thinking of buying a used module from ebay and eliminating that- silly idea?
Cheers
Chris

Before we go any further lets be sure about this. Its the Ignition Control Module ICU which is just behind the steering head beneath the top frame rail.  The Engine Control Module ECU is mounted under the seat above the battery.
The ICU supplies an earth to the starter relay if the engine isn't running or running below 711rpm.
That earth can also be supplied from the neutral light and the clutch switch
The ECU has nothing at all to do with supplying the earth to the starter relay.
If you go to the portal page and under interesting links there is a page for trouble shooting EFI/Ignition system if you follow that you should be able to find where the problem is.

Just curious but where did you get the 711 RPM number?  (I'm not doubting you, just curious.)




The voltage that comes to the starter button from the gear indicator (a.k.a. N light) or clutch switch is 12V+ and is sent to the starter relay via the black/yellow wire to the 86 terminal of the starter relay.

The ground for the starter relay comes to the 85 terminal via a brown/red wire from the ICU.

Just curious but where did you get the 771 RPM number?

Ingapedia I believe but I think I have seen it else where. Maybe it was BMWs workshop manual. I will search but my computer is as big a mess as my shed so be patient.

Well I must be getting better at searching didn't long at all
A lockout feature is also included to prevent the starter
motor from operating if the engine is running. Power to the
starter relay is shut off by the ignition control unit if engine
speed is greater than 711 rpm .

Page 299 Clymers

Yeah that's right    it 's 12 v that is supplied by the neutral light and the clutch switch not earth

ThanKS for all this advice. It is the ICU under tank below headlock. UK seems to refer to this as An ECU sorry for confusion. I can get a module on eBay for 20 pounds so will try this, as I think the earth is not switching to connected within the ICU properly,cheers

Then of course there is the fact it wont fire either (as well as crank)

Ah Ha We need a standard glossary for parts  Lets start with this A thingy will henceforth be called a whatsit any more brilliant ideas.  

The "Thing" being fried would explain both things.

New ICU (and brushes for alternator) has fixed the issue. Running nicely again, thanks for advice

Is it an idea to have a list of parts here that people can use when fault-finding? I can imagine a list for the antipodians, UK/Europe, North America etc where we can list which parts (particularly the expensive ones like ICUs and ECUs) that people can use to temporary change their part with to check function? Most of us have some parts stowed away that might come in handy when others want to do a quick check? Idea??

true indeed rene

although some of us have a good support network for testing ...there are many who don't have the contact

ReneZ wrote:Is it an idea to have a list of parts here that people can use when fault-finding? I can imagine a list for the antipodians, UK/Europe, North America etc where we can list which parts (particularly the expensive ones like ICUs and ECUs) that people can use to temporary change their part with to check function? Most of us have some parts stowed away that might come in handy when others want to do a quick check? Idea??

When I had an ICU problem 88KE offered to swap them to check them out. As I was reasonably sure it was my problem I calculated that at least 3 sets of postage would be close to cost of getting a replacement from Motorworks. But the idea is sound. I had never met 88KE at that time but finding someone so helpful led to us meeting up and finding some new friends.

No worries , I do have a few spares and if there was an ask I would offer.