I covered to this point on my original thread but since it will now start and run I will think it may be an unrelated issue.
85 K100 purchased a couple weeks ago as a non runner.
I replaced the ICU, plug wires, and plugs and the bikes fires immediately on cold start.  It warms up, surges RPMs, won't idle, and dies.  On warm restart attempts it behaves almost as if I'm back to square one: short cycles of the starter spinning, plenty of flow into and out of the tank . Suggestions made to check the fuel pressure regulator, vacuum pipe to it, as well as making sure the previous owner replaced the temp sensor with the correct part and didn't use sealant tape.
I'm also going to go through all connections including ICU and ECU with contact cleaner and dielectric grease.
Any other suggestions welcomed.
I did make it almost around the block before I found out these boots were made for pushing.  Cheers to that!!

New fuel pressure regulator, and it's vacuum hose is good.  There is good ground at temp sender and the PO stated confidence in it being the right one.  
I hooked up a test light to 12v+ and  started the bike.  I inserted the test light probe into the red/blue and red/black connectors while running to watch the ground signal.  That ground signal was definitely dropping away and causing the bike to die.
The coils, plugs, plug wires and ICU have been replaced and doing so has the bike cold starting great but dying and losing the ignition ground signal when it warms up.

The HES can fail when heated up. Probably worth checking out.
Regards Martin.

It's been replaced in an attempt to get it running by PO.  Also, does the Hall sensor have any bearing on starting?  I thought at starting RPM it wasn't in the loop?

You stated that it starts fine when cold but plays up once it warms up. "The coils, plugs, plug wires and ICU have been replaced and doing so has the bike cold starting great but dying and losing the ignition ground signal when it warms up."  It's worth rechecking.
Regards Martin.

Now that I am in the "warm but won't restart" condition and know that I'm losing ignition signal, I tested ICU connector wires 9&14 and am getting full 12v while the starter is spinning.  The troubleshooting guide says it should be in the 1.5-4v range.

I get the same voltage using the old ICU.  What is responsible for dropping that voltage down?

BespokeVillainy wrote:Also, does the Hall sensor have any bearing on starting?  I thought at starting RPM it wasn't in the loop?

If the Hall sensors during cranking or running are not outputting an engine speed (TD) signal to the ignition control unit, or the ignition control unit can’t interpret it because it is faulty, the spark plugs won’t fire correctly and fuel injector relay function will also be affected.

I'd say that your problem is heat related. I'd try heating various components with a hot air gun and see what readings change. I've also resorted to packing crushed ice around components to confirm that the component is overheating.
Regards Martin.

Going to try and track down an LED to test the sensor

+1 on cooling the various electronic components when the engine is warm. Instead of the crushed ice, you can also use a freeze spray that comes in an aeresol can.

https://www.crcindustries.com/products/freeze-spray-10-wt-oz-14086.html

So I just pulled the Hall and noted a piece of what feels like old gasket sealer off of the ring and you could see what looks like b

urnishing.  The Hall sensor looked fine.

I have 20ma 12V LEDs coming tomorrow.  I'll run the hall test cold and then heat it with a hair dryer and see if they fail.

Looks like your 'bit of old gasket sealer' has done a good job of scoring and marking the rotor. Whatever it is, it shouldn't be in there and is possibly the cause of your misfire by getting bits of itself jammed in the hall sensors and then knocked out again as the hole comes by.

BespokeVillainy wrote:Now that I am in the "warm but won't restart" condition and know that I'm losing ignition signal, I tested ICU connector wires 9&14 and am getting full 12v while the starter is spinning.  The troubleshooting guide says it should be in the 1.5-4v range.

I get the same voltage using the old ICU.  What is responsible for dropping that voltage down?

Also, because it's an on and off pulsing it's hard to measure with the direct current Voltage range. Your reading is what you would expect with DCV.  If you set your multimeter to ACV you will probably get within the range predicted in Bert's guide.

It might be worth looking at the temperature sensor again cause even though the previous owner says he is confident he got the right one, maybe you shouldn't be confident since he sold it as a non runner.

daveyson wrote:Also, because it's an on and off pulsing it's hard to measure with the direct current Voltage range. Your reading is what you would expect with DCV.  If you set your multimeter to ACV you will probably get within the range predicted in Bert's guide.runner.

As daveyson indicates, wherever the test shows a measurement of Volts~, it means measure Volts AC.

That's a hard one to get used to.
Hoping to have time to get on it this weekend.  The LEDs I ordered arrived too.

So I just tested both HES sides and both sides would kill the LED light cold as well as heated with a hair dryer to the point I couldn't hold the metal plate.
I guess I will focus on the temperature sensor next since it seems to die every time as soon as the bike warms up.
Fingers crossed.

BespokeVillainy wrote:So I just tested both HES sides and both sides would kill the LED light cold as well as heated with a hair dryer to the point I couldn't hold the metal plate.
I guess I will focus on the temperature sensor next since it seems to die every time as soon as the bike warms up.
Fingers crossed.

Temperature sensor does not cause a no running situation but it can cause excess fuelling by thinking its cold and over fuelling to compensate causing it to die.

If it thinks the bike is hot it inhibits a restart but does not cause it to stop.

If you change it make sure its for a 2v engine as the 4v looks the same but its not.

I wondered if it impacted spark or fuel.  Thanks for that.  Would it be the same for air flow/air temp?
Whatever it is, it definitely is killing spark.  I watched it start missing and then die with the test light on the coil connections.
Thanks again.

Losing spark could be a failing coil. Early models had coil problems that led to a redesign around 86-87. A failing coil can sometimes work when cold and fail when hot for a while before completely going bad. If you replaced with an early coil, you may not have completely eliminated the coil as a source of the problem.

When you lose spark, is it on more than one cylinder? Are you losing spark on a pair of cylinders that share a coil? If you swap coils, does the problem move to the other cylinders?

Point-Seven-five wrote:Losing spark could be a failing coil.  Early models had coil problems that led to a redesign around 86-87.  A failing coil can sometimes work when cold and fail when hot for a while before completely going bad.    If you replaced with an early coil, you may not have completely eliminated the coil as a source of the problem.  

When you lose spark, is it on more than one cylinder?  Are you losing spark on a pair of cylinders that share a coil?  If you swap coils, does the problem move to the other cylinders?

If you haven't done the coil check you should do that first. I assumed it had been done.

Early ones are very very prone to this and failing after getting hot, been there. The coil cover doesn't fit if you mix old and later coils, either 2 old or much more preferably 2 later ones.

I'm going to try rigging test lights to both coils at the same time and see if the missing and dying are the same.
Thanks!
If I can make the test rig stable I'll try and get video.

A coil issue affects one or both of 1/4, or alternatively one or both of 2/3. 1/4 fire together at the same time, 2/3 then do the same. 

The test is not fully reliable as it does not pick up if its failing under load due to weakness of spark.

I understand the batch fire of the system.  My dying happens both at idle as well as higher RPM when the bike warms up.

I just attempted to  test the secondary grounding of  Both coils at the same time using LEDs I picked up to test the HES but as expected I'm cooking them and have to quickly put my incandescent test light in as a substitute for one. I have also noticed that I seem to have lost my smooth idle.

I'm definitely losing the grounding signal of the blue/black wire to the coil.  I can swap it and the black/red wire  and the problem follows the wire regardless of the coil.  It is also independent of either of the 2 ICM units I have.

Thinking about trying a jumper wire from the ICM plug back to the coil to see if maybe it's a bad electrical connection along the wire.

BespokeVillainy wrote:I'm definitely losing the grounding signal of the blue/black wire to the coil.  I can swap it and the black/red wire  and the problem follows the wire regardless of the coil.  It is also independent of either of the 2 ICM units I have.

Anyone fill us in on the grounding?

Is it grounded through the ICU, possibly pointing to a fault in the ICU unit itself or in the plug connector?

Back to the known good parts bit. That fault has happened to other ICU units so possible to have 2 faulty ones. If I am right the ICU controls that earth. But if the earth is degrading does it mean the fault is in ICU or the other end as in a poor/damaged cable? The ground signal comes FROM the ICU? The ICU 'opens' and 'closes' the earth to control it? 

Does the rev counter behave normally during this?

I saw that the other her blue/black wire goes to the rev counter (tach) and it does behave normally just showing the R.P.M.s dropping as the ignition misses.

I cut the blue/black wire going to the rev counter just in case there was a short along it's path and got the same result.  Sudden drop in the ground signal on the blue/black coil wire when it warms.  I immediately tried swapping the ICU and it changed nothing.  Running out of ideas...

BespokeVillainy wrote:What sensor gives the blue/black (#9 I believe) it's ground?  The black/red coil wire (#14 I believe) functions normally.

Attached is an extract of the engine management schematic showing the ignition control unit and its coil wire terminal connections: the black/blue (sw bl) wire to terminal 14, and black/red (sw rt) to terminal 9.

When the engine stalls after warming up, are any of its spark plugs wet? 

Regardless of my hair dryer testing, If the two Hall sensors work independently to give a signal to each coil wouldn't it make sense that one might be failing at warmer temps?

Yes, the plugs get wet from the injectors pumping with no spark

It's the signal from the top sensor that allows the ICU to send an on and off ground through the black/blue wire.

BespokeVillainy wrote:Yes, the plugs get wet from the injectors pumping with no spark

If you mean "all the plugs", you indicated that one coil was firing and the other would quit; the engine ran then stalled so half of it had spark until it stalled. Is that the case? The reason I'm asking is that you asserted previously that both hall sensors were operational. 

If both Hall sensors function, what could be happening is the air flow sensor/ air temperature sensor is sending faulty signals to the ignition control unit so the fuel injection unit can't interpret them optimally when it receives them, or the signals from the air flow meter are correct but the  fuel injection control unit is fails to interpret some of them correctly because of an internal defect.

If the signals from the air flow meter are incorrect the engine could start then stall from flooding because the mixture isn't being leaned as the engine warms.

Does the ICU get a signal from the air flow meter?

Also, just thinking that the engine flooding from fuel wouldn't kill the signal from the a single secondary coil wire so sharply would it?

All things equal a failing air flow sensor affects all 4 cylinders equally. Filing Hall sensor only affects 2, 1/4 or 2/3.  Important to clarify if all plugs are same.

Outside of something crazy going on inside 2 different ICU the HES was the only thing I could come up with that would stop the signal to 14 without stopping it to 9.  Assuming the hair dryer didn't get it hot enough, I ordered new HES set.
Will check back in after it arrives and I swap it.
Thanks.

Is this any good?

http://www.kforum-tech.com/electrical/EFI/bike-wont-start-EN.htm

It is a wealth of knowledge and I reference it often.

Update:
Even though it passed away he hairdryer test I decided that one of the HES dying at running temperature was the only thing that made sense (to me) that could kill the ground signal to a single coil.  Since I had swapped the ICU and was getting the same failure mode I though while possible, it's unlikely that two ICU would be failing the same way.
I just replaced the HES and it ran well into warm temperatures.  I could turn the bike off and get quick restarts. It never made the fan come on but both radiator hoses were toasty.  I'm going to button it all back up and see if circling the block (when the weather clears) will prove victory!
Thanks for all of the help getting this far!!

6 miles without a hiccup.  Calling it cured!  2 days ago I got the all clear from cancer.  It's been a great week so far

Thanks for the help.  Now I can see I want bar risers.  I'm not used to riding on my wrists

BespokeVillainy wrote:6 miles without a hiccup.  Calling it cured!  2 days ago I got the all clear from cancer.  It's been a great week so far

That's excellent but sounding like you have contracted K Pox.!!!

That's great news! On both counts, especially the second.

Definitely!!

Life happens, be there.
I love Great Good News
Ride on.
Shep