Hello everybody.

While riding, I lost engine power and bumbled to a stop. All electronics were still up.
The starter turns vigorously, but the bike never fires again, not even for a second. Into the garage it goes.
One year later...

'85 K100RS

Problem: Cranks, but no start. No other apparent electric issues.
What I did:
-The obvious stuff (fuses, connections, N, clutch), Crazy Frog's guide
-Bought a terrible looking hall effect sensor and swapped it in. No effect. Mine might be fine. Both might be dead. Now I'll test instead of throwing money at it.

What the bike does:

-Starter turns
-Fuel pump runs
-Pressure at rail, injectors can pass fuel & are not stuck
-all 4 injectors do NOT fire with rail removed from engine while cranking


What I am doing: 

-Buying another multimeter (don't lend tools)
-Testing the airflow meter 
-Testing both HESs
-Asking you for help

This doesn't sound like the normal HES story, does it? Never had symptoms before this. Died once, and never started, or even burped again. 
The bike saw 48hrs of heavy rain just before the ride...

This bike has seen a lot of moisture over its mostly outdoor life. Dead Jetronic/Fuel injection "computer"? AFM?
The FI computer needs an RPM signal from the ICM/HES and what else to send the "squirt fuel" command?

Thank you, 

Moore

sounds like the efi computer (under seat ) big plug has become dislodged
there is a spring type clip that holds it in place , which you should be able to see through a hole in the toolbox (above the computer )

in my past this has come loose for me a couple of times (after playing with stuff )  usually after a pot hole hit or something

yes all electrics good , no injection

good luck

The jetronic connection is good, the latch feels quite secure. Ignition control module connection feels good too. All other connections are solid. 

I have a multimeter. I'll go down the line with it. How often do the 80s Jetronic computers go out?

When you wrenched this for two weeks, was the tank cleaned, the fuel filter replaced and were all the injectors checked for spray after you were finished?

I will give odds on it being the ECU once they get wet it usually spells the end for them and they get wet innards very easily due to a rubber seal that rots with age.

You have made no mention of spark or spark plugs. What's the story there?

Might be ECU connector also.  Even though the cable housing might be secured to the ECU enclosure, it doesn't mean that all pins are making contact with their counterparts.

Disengage the ECU connector and inspect all 35 pins of the female connector.  Look to see that they are intact and would make solid connection.  Have you cleaned the connections with contact cleaner like DeOxit?  If not, do so.

Inspect the housing of the ECU for obvious signs of distress and damage where water might find its way in.  If there is signs of water ingress, Rick's conjecture might be true.