hi all, i am new to BMW and to this forum. i recently bought a 85 k100 not running and am hoping to get it going soon. I've read great things about the bike and look forward to putting some miles on it. i have done some digging on trouble shooting but no luck so far. if anyone in central or north Texas wants to help take a stab at it I'd be grateful. at this point I'd be willing to pay to get it working but am apprehensive about taking it to a dealer since it's an older bike and may be the first one the tech has ever worked on. thanks all! Chris in temple

i guess i could include some more info on the condition. the previous owner rode it daily for about twelve years, up to 100k plus miles. on his way home about three months ago it suddenly died. he parked it and got a 2005 model. so far I've verified that the injectors are squirting gas and the plugs are sparking. the old plugs were pretty black and sooty when i replaced them with ngks. it occasionally backfires when i turn it over, but no running.

Oh you are close to having it going. I would check the main connection to the computer under the seat. Plug and unplug a few times and see what happens. Also there is a temp sensor wire at the front left side of the engine. If that is corroded or broken off the sensor it will give a no start condition. You will likely have to remove the air cleaner box to see it. Also buy a can of DeOxit and treat every electrical connection.

When you push the start button do you hear the fuel pump whiring, it should run for 1.5 seconds after the start button is pressed. Also check the connector under the right side cover which goes to the tank or it could with an 85 be under the left side of the tank and push up into the socket. Make sure there is no corrosion and clean well with the Deoxit, just giving it a bit of a wriggle can help diagnose but clean it properly if faulty.
If no luck there get back to us so far we have managed to get all commers going.

Oh yeah welcome to the forum good to have you along

Rick I figured if the plugs were wet the fuel pump must be a go... And he has fuel spraying out of the injectors.

club_c wrote:Rick I figured if the plugs were wet the fuel pump must be a go... And he has fuel spraying out of the injectors.

I am not real with it today my pain is in front of the meds, my back is giving me heaps.
Still worth checking the connectors if they are intermittent it will give problems. Check your coils and leads as a nice fat spark at atmospheric pressure can turn to a pathetic thing at compression also the connectors to the ICU right up front under the tank.

There's great troubleshooting information on the download site.

Sounds like your onto it, must be close to running, so many connections and semiconductors, heaps of opportunities for a no go, amazing how reliable the Ks are.
The current generation of bikes are imposssible to tweek without all the techno even a red radio wifi key my ducati mate tells me, makes you wonder if they have a useby date programmed in ? Ks don't keep us posted.
Rick

Look at the earth connections under the tank, there should be good contact, best to remove them clean up all the surfaces and refit. As said in some earlier posts clean all of the electrical connectors.

chris ...might be worth looking up the fault testing for hall efect sensors (ignition timing )

but i agree with club c ...have a good look at the temp sensor ...just behind the radiator

this governs in many ways, the mixture= fuel fed by the injector controller under the seat

pin 10 and earth are the measurement locations for this

there are a few good threads in the forum about this as well ...

try the search function

welcome aboard

Welcome Chris. good luck with getting going - it will be worth it.

88

I had some problems last year, they were cured when I replaced the ICU unit up behind the forks, its under the gas tank. Worth taking it out and cleaning all the connector pins. It seems a few sensors connect in here, the difficulty is that a bad connection may lead you to suspect a faulty sensor when the connection is the problem. There are also earths that should be opened and remade.

As everyone says the electrical connections are the weak point, once you have them sorted you are highly likely to have it solved.

All this means you will have the gas tank on and off a few times. If you can you should replace the fuel lines - if they are perished at all that may weep causing a fire risk. BMW line is not expensive and if you make them longer you can do a lot more without having to remove the gas tank each time you need in there, ie access the relay box, the connectors, the rad top up.

A little patience is needed but it will be well rewarded.

quick update. I pulled the bike out and started messing with it this morning. I unplugged the computer a couple times and replugged with no luck. Compression is around 160psi with open throttle via my tester. I looked for the water temp sensor. It is under the radiator on a hard line, right? I want to test it but can't find out where pin 10 is on the computer plug. I noticed there are two loose wires zip tied to the wire leading to the temp sensor, no idea what they are, couldn't really tell what color they were. I'll pull the tank off and get a better look after lunch. I saw the boots between the injectors and the head are starting to crack. I may test the hall sensor this afternoon, haven't looked into what all I'd have to pull to get to it yet. The engine is pretty oily, may clean it all down before anything else. The amount of electrics on this thing is a little daunting; I'm used to working on bikes with carbs and points. Many thanks already.

Dont despair. Once you have it running you will realise all the time you spend with carbs and points, especially if you have 4 carbs and having to keep them in balance and clean etc etc. Most of us have been through the carb/points/tappets four pot Japanese superbike that needed constant adjustment and you will have none of that. You are picking up on some previous neglect and after that you should be good.

Have you cleaned the tank and replaced the old fuel?
A even a quarter of a cup of Old stale fuel, left in the tank if refilled will prevent it from starting up when cold.
By the way....if you want to use the forum effectively, you should answer the various members' questions when asked so that we can help you. Don't go charging in and working on too many things at one time for fear of "un-fixing" something that isn't currently broken.
Please post pictures like of the wires you found at the coolant temperature sight, so your question can be addressed.
We'll get you going.

I'm going to try to attach pictures of the wires. https://docs.google.com/file/d/0B39Aqze2NQtYX1YwOUx6MmlBNDA/edit?usp=sharing

@ibjman: Thanks for the tip. The fuel had been drained by the previous owner before he put it away for the three or so months it sat before I got it. I think I mentioned that the no start situation was pre-existing, in fact it was the reason the previous owner got rid of it. I am trying to explore all the suggestions I'm receiving, and believe me when I say I don't plan to intentionally do any unnecessary work.

Does anyone have a link to a diagram showing how the pins on the computer are numbered? I see that pin 10 to ground is the way to measure continuity through the temp sensor, but I don't know which pin is pin 10.

To all who mentioned checking the front control unit connections, I'll do that this evening. And Rick G, more on the coils and leads: what specifically should I check? Resistance through the leads? The spark is blue but may not be as strong as it should be. Thanks

chrslws wrote:To all who mentioned checking the front control unit connections, I'll do that this evening. And Rick G, more on the coils and leads: what specifically should I check? Resistance through the leads? The spark is blue but may not be as strong as it should be. Thanks

Check for corrosion at any of the plug points and connectors, measure the resistance of the leads should be 5000 ohms and give the leads a wriggle to make sure there is nothing intermittent. Measure the resistance of the coil primaries and secondaries. Primary is where the 12v connects around 4 ohms and secondary is to plugs about 10000ohms
Plugs should be NGK D7EA ir equivilant.

RicK G wrote:
Give the leads a wiggle to make sure there is nothing intermittent. Measure the resistance of the coil primaries and secondaries. Primary is where the 12v connects around 4 ohms and secondary is to plugs about 10000ohms
Plugs should be NGK D7EA ir equivilant.

Which one?

chrslws wrote:
Does anyone have a link to a diagram showing how the pins on the computer are numbered? I see that pin 10 to ground is the way to measure continuity through the temp sensor, but I don't know which pin is pin 10.

Send a pm to Crazy Frog (Bert) if you haven't already. He will send you the password to the download section.
More stuff in there than you could poke pin 10 at.

rossco

and I would suggest those wires may be for an auxiliary temp gauge?

Quick update: checked the ignition module connector and the connections appear to all be clean. I cleaned the grounds on the center of the frame under the tank and on the left in front and below the battery. I guess I should be able to find the DeOxit product at Radio Shack? Any specific instructions for use or just whatever the can says?

On an unrelated note, I repainted the fender, seat pan, and side covers and they look pretty good, although I still need to buff them. Debating whether to paint or polish the tank. I feel like I got ahead of myself painting all that stuff before getting the bike to run, but I had everything out for another project.

Testing resistance on the coils and plug wires might have given some fresh insight. Plug wires were each around 8800 ohms, except for one which I couldn't get to read no matter how I prodded it. It sparked when I put the plug in, but could never get a clean spot for a reading. Primaries showed 8.5 ohm (1/4 cyl coil) and 9.3 (2/3 cyl coil).

BMW provided some better ignition coils to replace the early ones. The originals where all Black. The better ones have orange ends on the towers where the plug wires connect.
I spent weeks trying to get mine running right till I replaced those coils with orange ones. sounds like your primary readings are high? i'm thinking like 2-3 ohms here? your reporting 8?

try this or google k100 wiring diagram

Quick resistance check on the coolant sensor shows 2.37k ohms at 67 degrees F. Looks close to the chart on the troubleshooting page, maybe a little under the curve.

Good job. The coolant sensor is a less likely cause of probs. They are quite dependable as is (most?) of the wiring to sensor circuits.

I get a great deal of value out of that elec. schematic.
I printed out the largest possible copy on my 11X17" printer,....... printed the similar, "simpler" "Electronic Ignition" diagram on the opposite side and then laminated the whole piece.
I can not make notates, etc wherever I wish to on it with a grease pencil & wipe them clean when finished.

On the diagram, is there a way I can get a higher resolution version? When I open it after saving, I can't blow it up without it going fuzzy.

So, at this point, is it possible that my troubles are simply due to needing a tune up (plug wires and coils)?

try this link, Im nit sure how big you can magnify the image without losing focused resolution.
http://home.comcast.net/~smithduck/bmw/kwiring/kwiring.htm
Rick

Thanks Rick, that's better.

planning on ordering plug wires. are the new ones from Beemerboneyard worth buying or should I try to get OEM? http://www.beemerboneyard.com/12121459876k100.html

I dont think you would get a better price for new leads.
The Beemerboneyard had good prices but by the time the USPS gets its lb of flesh it's not worthwhile buying from him in Australia.