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85 K100 - bike won't start

Last edited:
BTW, I don't think I reported on my fuses:

1: 12.2V
2: 11.8V
3: 12.2V
6: 0.0 (!)....but the fuel pump does run and I do have fuel pressure. So IDK.
7: 12.2V
 
If it's like other older K bikes - the pump only runs for a second when you turn on the key, to pressurize the system, then stops; it resumes when the engine is running.
You might need a third hand (or some little clips) to catch the start-up voltage.
 
Thanks, Paul - makes sense.

And I tested the injectors individually with a 9V battery....after some reluctance, each one of them fired a stream! So my assumption they were all clogged was wrong.
Looks like I have a electrical cause after all. Will test each lead tomorrow when I get the LED tester.
 
They should not be reluctant to squirt... should be immediate, but I don't recall if the lower voltage (9 volts) would do that (YouTube wants me to sign in, grrrr). Possible junk inside, or a bad pintle?
 
Latest: I tested the FI leads and got a voltage flash at each one. Reconnected and now I have a fine mist from each injector! Odd turn of events, but I'll take it!
Will do some more injector cleaning and replace the O-rings. Might as well replace the spark plugs while I'm at it. Then will give it a crank. 🙏
 
Update - looks like I DON'T have much power coming to the FI harness. I used Lee's recommended noid tester and got no flashes at any of the plugs....just the dimmest of glows.

The good news is the injectors work/spray with the 9V battery test and I've got pressure in the fuel line.

I know there are threads out there about troubleshooting where the voltage is breaking down between the battery & the FI harness. But I'll take any recommendations or advice!

(Also, don't use the ear plugs for FI hole plugs....I almost sucked one into the cylinder :eek:)
 
rawhites said:
Update - looks like I DON'T have much power coming to the FI harness. I used Lee's recommended noid tester and got no flashes at any of the plugs....just the dimmest of glows.

The good news is the injectors work/spray with the 9V battery test and I've got pressure in the fuel line.

I know there are threads out there about troubleshooting where the voltage is breaking down between the battery & the FI harness. But I'll take any recommendations or advice!

(Also, don't use the ear plugs for FI hole plugs....I almost sucked one into the cylinder :eek:)
Click to expand...
Besides a general check of the wiring harness for obvious problems, I'd suggest removing and cleaning the starter. The classic K-bike electrical system uses the starter as one of the main grounds and if it gets dirty inside you can get all kinds of electrical problems. I had this happen with my 1990 K1 with only 14,000 miles on it. The turn signals would flash opposite of what I selected or go into 4-way mode and other issues. The starter was filthily - don't ask me how - but once cleaned everything worked perfectly.
 
pauls1150 said:
I still haven't found a sidestand switch in the MAX fiche.... 🙁
But here's a pic from them showing the clutch switch, item 6.
View attachment 101215
Click to expand...
Hey Paul - coming back to this possibility of my problem lying in the clutch sensor not working properly....if it isn't working, would I still be able to crank the starter & get spark, which is the case currently?
It seems the primary issue is no power to the fuel injectors, so I'm trying to find that root cause.
Also, to inspect the clutch switch, I assume I should do a continuity test and "clutch out" should equal no continuity and "clutch in" should give me a continuity signal?
Thanks!
 
I am not sure if this helps, but here goes. If it cranks when in gear and the clutch pulled it is not the clutch switch.

These bikes are a bit weird compared to later models. In many later models both ignition and injection are controlled by a single Engine Control Unit (ECU) . On the K100 and K75 models this is not the case. Ignition is controlled by the Ignition module mounted on the frame up under the fuel tank. Fuel injection is controlled by the LJetronic module under the seat area.

Given what I have read here so far it sounds as if the ignition is working but that the LJetronic is not sending appropriate signals to the injectors, So it would seem to be a bad connection or wiring, or a faulty LJetronic unit.
 
In light of Paul’s clarification it might be time to pull the big connector on the LJetronic and check it for corrosion and cleanliness? And check grounds, always on the older brick-k bikes check the ground connections.

Best,
DeVern
 
Thank you, Paul & DeVern! I’ve done a lot of Deoxit work on the connector to the ECU…to no avail so far. Not sure what else I can do there.
I’m going after all the ground points around the bike with fine grit and deoxit.
So based on my symptoms, is it worth working on the starter relay or on rehabbing the starter itself?
I’m game for any sequence, so long as it’s worth it!
 
I don't think so. The starter grounding controls the load-shed relay and ignition isn't one of the things that you would want to load-shed.

The diagrams show the FI relay sends solid power to the injectors and the Jetronic provides a pulsed ground (which is typical on the Motronics as well) so start with checking the output from the Fuel Injection relay and then see if the same power is available at the harness plug and at the injectors themselves.
 
Thanks, Anton - if you wouldn't mind providing some basic steps on identifying that relay and testing that relay output, I could use the guidance....my electrical knowledge is limited, let's say. And looking at Clymers & Haynes, I'm surprised with how little detail there is on the relays....there's not even a clear depiction of which is the FI relay (Clymers identifies two "fuel pump relays" and Haynes doesn't say anything about it), much less how to test them for voltage & continuity.
I really appreciate the help!
(BTW, not sure if this is meaningful, but I have power to the turn signals & headlight, but not the horn...And confirmed, the starter cranks when is in gear, clutch pulled in. Though clutch is stuck for now.)
 
Start by looking at whatever wiring diagram you have. I'm looking at a K75 diagram (which is probably really similar) and I'm following this:
Red (Battery +) to ignition switch
Green (switched power) from ignition switch to kill switch
Green w/yellow from there to lots of things including a control terminal on the FI relay. So if you have the key on, kill switch up, you should have 12V there.
The Ignition module grounds the other control terminal of the FI relay on a yellow w/purple wire, sending power from red (unfused, unswitched battery +) over green w/red to the injectors.

So find the relay in the box under the tank. It'll probably have wires colored:
- green /red
- yellow /purple
- red
- green /red (x2)

Check the voltages at those wires with the key on and the kill switch up to see what's happening there. It will probably only get the ground from the ICU when you crank the engine, but you can check the green /yellow for voltage without cranking.
 
Here's what I got:
- Red (30): 12.4 at no crank; 11.0 at crank
- Grn.ylw (86): 12.2 at no crank; 10.62 at crank
- Ylw.brwn (85): 0 at no crank; 0 at crank
- Grn.red (87): 0 at no crank; 0 at crank1
 
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