Hello! 

I have a 1985 BMW k100 that started to run really poorly recently. It was overdue for some maintenance since i bought it, so i decided to use this opportunity to fix some things, and conduct some preventative maintenance. 

Through my testing, i've found a few issues:

1. 2-3 coil had no resistance between the high voltage towers, the 1-4 coil had 10.5 ohms. Both coils had 2.5 at the low voltage plugs. Coils were the original old black versions. Just ordered some new red tops. 
2. Fuel pressure bounced around significantly when i tested it, but stayed between 35-39 psi.  Upon shutting off the bike, the pressure dropped to 0 almost immediately. Fuel pump and filter have been replaced fairly recently. I took this to mean an issue with stuck injector/FPR. I've ordered the new 4 hole version of the injectors, and a new FPR to eliminate any issues with the fuel system. 
3. installed a new air filter, checked the paddle in the sensor while i was doing so and it moved freely. 
4. The z crank case breather hose was cracking, but didn't look like it had cracked all the way through yet, I went ahead and ordered a new one. There was a little bit of oil in the hose when i removed it. I wasn't sure if this is normal. 
5. the hose connecting the bottom of the FPR and cylinder 4 was in mediocre shape, but didnt have a clamp on it where it connected to the cylinder. I've ordered a new one, but does it need to be clamped?
6. bought and will install a new HES.
7. when i removed the top of the reservoir for the rear brake, there was only half the fluid left from when i topped it off a year ago. I went ahead and got a new reservoir and new rear brake lines. Hopefully thats the issue and i don't have to rebuild the caliper or cylinder. 

Anyway

I'm continuing to test the bike as i go. It's never run great (i've had it for 3 years, but never had a chance to dive into it til now), it always seemed to stumble on itself if given gas too quickly, and has progressively idled worse, until it started to noticeably hunt in idle which is why i've started this process.

Anyway i live at 7k elevation, and came across some information about a high altitude plug on the bike. I've looked and looked and cannot find it. However I did find a plug that had been disconnected, and a plug with no connection to it. I'm trying to figure out what each of these plugs do(thinking one could be the high altitude plug)?! both have been unplugged since i bought it, so I'm interested in finding out how they affect the bike. 

Here are two pictures of the plugs. The top three prong plug was unplugged when i found it. 

The bottom two prong plug has not mate, and i'm assuming this is the high altitude plug? 

Good to see you and that's a good list you have there.

Mixed thoughts on 4 hole injectors for the 2v. I have done it and they increased consumption. I put them in and an immediate improvement. But a couple of thousand miles later put the old ones back,after them being cleaned and checked and one replaced and they ran just as smoothly. The 4 holes hit my fuel about 15%. Also get some spare injector seals, you need 2 for each so buy 10.....

That vacuum pipe has no clamps. Your 85 might just also have a fuel pressure sensor FPS, early ones do and I have them on my 83 and 84 Ks, it has a similar vacuum pipe to the front cylinder on the throttle bodies. Take it off and get 4, not 3 vacuum caps and replace the other 3 and put the 4th on to the spigot for that pipe. If you have an FPS it lives beside the fuel pressure regulator and has a single electrical spade connection. It does nothing. 

Fun sometimes in getting the air box off.....2 6mm allen bolts in the bottom, liberal WD 40 helps.

Run a check on the valve clearances and then balance the throttle bodies and air intakes.

On my Ks the fuel pressure drops immediately the pump is off, no residual pressure on all 3. FPR is getting expensive too.

Throttle position sensor may need a clean and reset too.

As you are in there, check the cooling fan is doing ok, not seized, it should turn freely by hand.

Draining coolant? Open the hose clip on the bottom hose into the water pump and not the drain plug. Much easier to seal after.

Neither photo is the high altitude plug.  You will find that plug near the top frame rail on the left side directly above the coils near the rear of the tank.

The plug is a round two wire plug about a quarter inch in diameter with a rubber sleeve around it.

The plugs in your photos might be for the fuel and temperature gauges or heated grips.

Working from the top down:-

Three pin flat terminals (brown, yellow/slate, blue/slate) = hazard switch
Three pin round terminals (brown, slate/blue, green/black)= connector for additional instruments
Two pin round terminals (brown, green/black) = heated grips

As you live at 7k elevation , you need to make sure the jumper pin is in. It can be tricky to see as it is the same color as the sheathing ie black. On mine it was tie wrapped to back of the left rear frame “triangle”. 
You are certainly attacking the problem from all side. I know how tricky  that can be as I recently had to do the same. I did the same sort of things you have done and the issue turned out to be a simple issue with an intermittent break in the plug lead. Do the basic simple things first . Checking for that pin would be the easiest part of the diagnosis.

Hey Everyone! Thank you for the help identifying the plugs! I found the Altitude Pug:cheers:

However, bad news. I've completed the work that I thought would fix the main issue, it hasn't. 

This was what in sounded like before the work:




This is what it sounds like after. 



Here's what I've done so far:

New red top coils
New Hall effects Sensor
New Z Crank case breather hose
New Fuel Pump Regulator
New Fuel Hoses
New Spark Plugs
New(Ish) plug wires

Here's what I checked. 
Plugs under tank
Plug into tank
Compression in cylinders is good 

I'm not sure where to go from here. I'll be syncing the TBs as soon as my gauge arrives, but I don't think that's the issue. I'm guessing it must be something with the ignition system, but I don't know. 

What do you guys think?

Check around the throttle bodies for leaks and synchronize. Have you fitted the new fuel injectors? Have you checked the mixture either with a gas analyser or the lean drop method?
Regards Martin.

MartinW wrote:Check around the throttle bodies for leaks and synchronize. Have you fitted the new fuel injectors? Have you checked the mixture either with a gas analyser or the lean drop method?
Regards Martin.

Thanks Martin.

I'm just waiting on my gauge, and I'll sychronize the TBs. 

The new fuel injectors are in, and they're the 4 hole. I bought them from someone who says they've been tested and approved before sending. 

P.S. when I pulled the old plugs, they all seemed very wet. That's why I'm guessing it's something with he ignition system.

Very wet plugs can be a case of a faulty temperature sensor or dirty  sensor connection that will also cause bad running. As far as 4 hole injectors, go a mates son is a auto electrician and his company does a lot of work with fuel injectors. Apparently apart from increasing fuel consumption there is no benefit due to the positioning of the injectors in relation to the valves. There is also more chances of the holes blocking due to their decreased size.
Regards Martin.

I’ve heard similar things from a few people about these injectors, but I wanted an extra set while I cleaned the originals, so I tried the 4 hole injectors.

I checked the ohms to the plug for the temperature sensor. It read 950. I ran the engine about 45 mins before I checked it for only about a minute, so I couldn’t tell if the sensor was reading high, or if the engine was still hot from previously running. I’ll check it tomorrow morning after it sits for the night.

When you say dirty sensor connection, what exactly do you mean?

Thank you for your help!

The sensor is sited behind the radiator on the left hand side. It is subjected to a lot of road spray and crap and eventually this works it's way into the connector and it starts to corrode and/or the road crap partially insulates it. In order to stop the ingress of water and crap I smeared heavy silicone grease or dielectric around the plug when I installed it. It can also develop a bad connection where it goes into the computer. The sensor should never be installed with Teflon paste or tape on it's threads as it is required to earth through the threads.
Regards Martin.

MartinW wrote:The sensor is sited behind the radiator on the left hand side. It is subjected to a lot of road spray and crap and eventually this works it's way into the connector and it starts to corrode and/or the road crap partially insulates it. In order to stop the ingress of water and crap I smeared heavy silicone grease or dielectric around the plug when I installed it. It can also develop a bad connection where it goes into the computer. The sensor should never be installed with Teflon paste or tape on it's threads as it is required to earth through the threads.
Regards Martin.

Thanks Martin! I JUST put the airbox in over the weekend... darn! I'll remove it again and check/clean the sensor plug this afternoon.

I just checked pin 10 with the engine cold, and it came back at 2.5k ohms, which I think is in spec?

Rockymountainmoto wrote:I just checked pin 10 with the engine cold, and it came back at 2.5k ohms, which I think is in spec?

2.5k is perfect.

Does that mean I can rule out the temperature sensor?