Please would anyone with a similar experience offer me any advice to get this bike back to its reliable self again.

I have replaced the FI relay and ICM under front of tank, (old one no output on pin #eight), and the fuel pump is fine. Replaced temperature relay and fan is fine, but still no start.

Based on heat stress, I replaced the HES, spark plugs and leads and HV coils and tested temp sensor, (both outputs OK), AFM, TPS, ECM and all good per Crazy Frog's troubleshooting guide.

Spark at plugs and fuel injectors all working, although I suspect spark may be varying in intensity.

Engine cranks well and battery good. Tries to fire, but will not start. Sometimes, for no reason, it does start when the starter is held down to continue cranking after the engine fires and then the bike runs up like new - everything works and it rides great. But when  it stops and is shut down, will not restart. Other times this procedure will not start the engine.

I also noticed that disconnecting the temp sensor on radiator seems to help to fire a bit more, but still will not start. Have tested sensor and when running, output is per graph in guide and when cold as well, so seems OK.

Does this sound familiar to anyone?

Thanks,

Gerry

Havn't had a problem with the ICU,  so I'm just guessing.

You replaced heaps of bits,  I'll guess you only have one problem, unlikely lots of things failed at the same time. Are all the replaced parts known good?

If my bike I would put all the original parts back,  then find where the fault is and fix it.



No ICU output from pin 8 could be due to a missing input, so maybe nothing wrong with the ICU.

Was the tachometer working, or anything else that wasn't working properly?

Have you inspected the throttle body manifolds, the crankcase z-hose connection to the air box and the throttle body vacuum caps for cracks? Have you inspected the fuel pressure regulator vacuum hose for cracks and for an odor of gasoline? Have you verified the fuel pressure? Have you verified that all the fuel hoses in the tank are in good shape, tightly connected and that the fuel filter isn't restricted?

How many kilometers on this moto?

My guru friend one day took to my 84 K100RT. Replacment plugs had improved the bike but not as much as expected.

Set about balancing throttle bodies by ear, then added the manifolds just to prove his work [as in show his skills] and then took off and cleaned the throttle position sensor. Vacuums and Z pipe known good and carb cleaner spray didn't identify any leaks. Ran good after it.

Thank you to all who have given me assistance with this.

Sorry to not have provided more info, but the parts I replaced were a precautionary measure to avoid having to strip the bike down in the near future due to heat stress related issues. When I did this I did it part by part to confirm the health of each of the existing items. In most cases the existing items were all good, but showed signs of heat damage to their cabling and connectors such as cracks and brittleness. It did id deviation from normal on 1 HT lead and 1 HT coil though which were replaced.

The difficult part seems to be to find the fault, which I agree is a single issue, as it seems to be intermittent. The temp relay was faulty and I suspect the ICM was causing the fuel pump problem and a new ICM did rectify this.

The really puzzling thing is that if it will start, everything seems to run fine. I suspect some type of intermittent fault that may not be obvious to find.

 I have inspected all the usual suspects for leaks and if these were present I would expect them to permanently stop the bike from starting. I assume that the timing and carb balancing are in order for it to run well when it does start?

There is plenty of fuel coming through. Although there is spark at the plugs, I wonder if this is intermittent for some reason.

Thanks,

Gerry

I hate intermittent faults, I am waiting on parts to update my bike due to it misfiring intermittently. I went for a ride yesterday and found the fault, it was one of the fuses not being held in the holder properly. I used a piece of tissue to pack out the holder and it holds all the fuses in place. Problem solved.
 I would suspect you have a loose connection somewhere, either one of the multitudes of plugs has green crusts or a terminal is loose somewhere.

What year is the K?
The early ones had a one-way plug in the tank as retour for the fuel.
Can be stuck, get all pressure of the pump on the injectors.

I had an intermittent problem with starting and engine shutdown at speed on the highway.  It turned out to be dirty contacts in the ignition switch.  They're 30+ years old now, have accumulated a bit of dirt in them, and it doesn't take much to interfere with the operation.  Even if it isn't your problem, it is a good preventative measure.

http://www.kforum-tech.com/electrical/Cleaning_ignition_switch/Cleaning_switch.htm

I purchased a 88 K100RS,only 31000ks.
having similar problems found most of mine as the crankcase breather hose. Has delt with the majority of poor running. although I do not know much of my bikes history replacing most comsumable parts as I go so I know whats good & bad getting there slowly but learning quickly.Have fun regards Poddy

gerryte wrote:Sorry to not have provided more info, but the parts I replaced were a precautionary measure to avoid having to strip the bike down in the near future due to heat stress related issues.

The really puzzling thing is that if it will start, everything seems to run fine. I suspect some type of intermittent fault that may not be obvious to find.

I can't tell from your response whether you inspected the engine for throttle body manifold, vacuum tube cap and fuel pressure regulator hose leaks but the moto doesn't need to be "stripped" too far down to do that. Are you referring to personal issues with heat stress keeping that from happening?

Anyway, to echo Stumpy and Point-Seven-five, the ground connections at the frame tube under the tank should be inspected and cleaned. All electrical connectors including the ignition switch connector under the tank should be inspected and cleaned. The ignition switch itself should be inspect and cleaned. These are all relatively benign tasks and should be considered the moto owner's equivalent of crocheting. Failure of connections is a common fault source of intermittent engine problems. Leave repair-by-replacement-of-parts to the authorized service centers.

Get an old fashion timing light and if you can start this relic again, attach it to each of the spark plug leads and observe for yourself whether the delivery of spark is intermittent.

Which parts are you receiving that might remedy problems?

To clarify, all parts fitted are genuine BMW from agent. I have checked the throttle body manifold, vacuum tube caps, fuel hose leaks and ground connections. Although the bike is old, it is in excellent condition with low 40k mileage for age, always having been garaged, serviced and cleaned so corrosion is not a problem.

The heat stress is to the components listed as the agent advised they see this frequently on Ks that run in very hot environments and it typically shows up as cracked rubber/plastic coverings/connectors and I found this on HES cabling although the HES unit was still functioning. The reason I changed them was to avoid having to remove the RS fairings each time I needed to do this.

I did check the ignition switch and the kill/stop/start switches and all OK and work with full battery voltage coming through and all electrical gear/lights working fine. I did not dismantle the ignition switch in case it pops apart like an old watch.

I will dig out my old timing light to check the spark plugs again.

I have not checked fuel pump pressure, but have visually seen all 4 injectors operating during engine cranking and had the bike running when it did start and no problem on the road, so I assume the fuel feed is OK?

Checked all fuses and again all tight and in order.

Perhaps somewhere, as Stumpy suggests, a loose connection in a connector, but where to look based on the symptoms? 

Thanks again,

Gerry

Could you list the things NOT done.?

Your timing light idea is good.

I wouldn't eliminate fuel pressure as it's intermittent. Were the plugs wet? Unplugging temp sensor helps (running rich) maybe points to lean mix.

Has pin 8 failed again? (pressing the button might be masking a problem) Maybe check the other outputs while there.

Is the tacho working and which cluster lights are working?

Has it died,  if so suddenly or slowly?

gerryte wrote: The reason I changed them was to avoid having to remove the RS fairings each time I needed to do this.
I did check the ignition switch and the kill/stop/start switches and all OK . . .
. . . so I assume the fuel feed is OK?
Perhaps somewhere, as Stumpy suggests, a loose connection in a connector, but where to look based on the symptoms?

You'll likely need to remove the tank to clean and inspect the ground connections attached to the frame and the connectors under the tank. Avoidance is futile. It's flawed reasoning to assume the ignition switch and kill switch are ok because you tested them. Your problem is an intermittent one; the switches can possibly function at one moment then fail at another from corrosion or other conditions within them or their connectors. Engine vibration can change the situation at any time. Heat can cause tenuous connections to fail until they cool down. Assumptions are distractions.

There is a series of orderly system tests within the troubleshooting guide in the site's Portal. Their accuracy is predicated on good ground and plug connections. Inspection is the only way to verify their condition before undertaking the testing. You'll need to look under the tank.

One plug that won't take much disassembly to reach is the Jetronic plug beneath the seat. Unplug it, clean the pins and sockets with DeoxIT electrical cleaner then plug it in tightly. A plug that is loosely connected or slightly corroded will cause intermittent running problems and it needn't be too loose or corroded to do that. Another is the 4-pin connection to the fuel pump. On your '84 moto, it's beneath the left side of the tank.

As Olaf suggests, list everything you've done.

As poddy suggests, have fun!  It's not about the destination, it's all about the journey—unless you need to get somewhere.

Do you have a good Battery?  Slave it with another one.
Is the Alternator putting out enough to charge the battery?
Is the positive lead tightly connected to the starter relay? 
Is the lead from the starter relay to the starter motor tightly connected?
Is the earth lead connected to the battery tightly?
You could check the resistance to ensure no broken strands.