Hi all - 

I have a 1985 K100RS.  Rider her to work and back home mostly, only 11 miles each way.  Over the summer I had several instances where she'd not want to re-start after riding only a few miles (leave home and stop for gas, for example).  Let the bike sit for a few minutes and she'd start no problem.  No issues with engine cut-out or missing when running otherwise.

Then, couple of months ago, she stopped completely.  Riding home the rpms wanted to drop below 1000 at idle - sitting at a stop light I had to rev to 1500rpm or more to keep it running.  Made it home, but in the last couple of blocks one or two cylinders totally cut out and just before I shut down the idle speed was down to 600rpm or so.

Replaced fuel filter, checked all 4 plugs for spark (all good).  Bike will crank, but not fire.  You can hear the fuel pump spin.

Took her to a vintage mechanic here in Seattle.  He checked the injectors and all 4 were spraying fuel, but interestingly would continue to spray for about 2 seconds after releasing the starter button.  He diagnosed a failed fuel injection module.  

Has anyone experienced anything similar with their bike?  I had a quick look at the EFI troubleshooting page in the portal and will be following up with this.  Also thinking of buying a used module to see if that helps with the fix.


Thanks,
Tony Marts

Spraying for 1.5 seconds after engine stop does not indicate that the ECU is faulty.
There is very obviously a faulty component but that diagnoses does not hold up.
Get the trouble shootong flow chart from the portal page and follow that, it will give you a good outcome with regard to the problem.
There are so many people who are only too fast to diagnose a bad ECU when in fact the only time I have seen one fail is with water leaking onto them. They are very reliable.

Thanks Rick.  I'm going to print out the troubleshooting guide today and start reading up.  The more I read and think about the problem, I agree that the ECU may not be the issue.

possibly one of the hall effect devices playing up

might be an idea to check the wiring under - around the timing plate at the end of the crankshaft ....corrosion could be an issue ...unobserved so far ?

a few around here have offered a plausible explanation to the dielectric of the insulation on the hall effect devices breaking down

but it is known that heat and missing  usually points to the hall effects sensors in many instances

just  a heads up ...the temp sensor attached to the water outlet from the head to the radiator  also has noted as having connector and ground connection issues ...which can starve or over fuel the system

many posts about this throughout the forum

good luck

Condition of the spark plugs will tell a little about what's going on... are they wet or dry after trying to start?

If the K is starting from cold and running for a while and the problem only arises after warming up the Hall sensor is a suspect.

If you use a heat source [hair dryer] on the front T cover and warm it up to operating temperature and then try to start the bike. If the problem shows up then you should be looking at the Hall sensor.

The temperature sensor Charlie99 mentions is also known but getting at it takes a bit of time and removal.

The module is normally reliable and the worst that seems to happen is poor connections at the plug.

Sorry for the late reply.

Plugs are wet.  In fact, there is so much fuel building up from starting attempts that it was leaking from the header pipes/muffler joint.  

Plugs are firing as well, you can see spark from each.

I plan on doing most of the checks in the trouble-shooting guide, even the coolant temp sensor (which will allow me to change to coolant anyway).

The hall sensor went bad on my first K75 and was eventually diagnosed by the dealer after much fiddling (they replaced the ignition control unit and checked fuel pressure, among other things).

I had this come up on mine and it was trash stuck to the bottom of the fuel pump covering the intake portion. Cleaned it off and she ran like a top.

With you describing how wet the internals are with fuel I would be getting the injectors serviced as they may be spraying all the time and not just when the ECU tells them to spray.
To clean them your self get a can of carb and throttle body cleaner and a 9v battery like is used in the household fire alarms. Use the 9volts to operate the injector and spray the cleaner through the injector and leave the injector sit for 30 minutes then do it again. Keep what comes out just to see how much crud comes out. Get a service kit which comprises new O-rings, filter for the top of the injector at the inlet and a pintle cap.
The small filter comes out by screwing a selftaping screw in gently and pulling it out.
Give the outside a clean and fit the bits, put them back and see how it goes.

Excess fuel could mean the water temp sensor (as noted above) is not grounding which tells the FICU its extremely cold so it pours on the fuel at startup. Easy to test. Just measure the impeadance on pin #10 to earth on the FICU plug. Should be reading 2.5KΩ @ 20°c

Well I finally got the bike in the garage and pulled the tank.  I've read through the troubleshooting guide from the portal and have a couple of questions before I dive into the checks.

I was able to pick up a 12V LED rated at 20mA.  I didn't see a current flow rating value in the guide for these, just want to make sure the current draw is ok before testing the Hall sensor and injector power.

Also, when checking the voltage values at the EFI and Fuel Injection female connectors I assume I'd ground the multimeter negative probe to the ground connector when checking any other given pin for positive voltage.  For example, on the EFI check, for Pin #6 (signal from starter switch), the you check for voltage between Pin 6 and Pin 1 (ground).

Full disclosure, I'm an engineer but for aircraft structure, not electrical.