Hi, I have an intermittent problem that has finally become a full time problem. I have traced it to the fuel sensor, great, but I cannot get a new sensor, my BMW agent promissed me a new sensor ten days ago. Apparently, BMW have parts supply problems in France due to a new computr program. Does anybody know how to test this so that I can at least be sure it's that? From what I understand, on the 85 K100, the one that doesn't have a fuel gauge, the fuel sensor tells the EFI unit if there is no fuel and shuts the engine down. I'd like to be able to fool it into thinking there's fuel because the faulty sender is saying it's out of fuel. Am I making sense? My other alternative is buying online, does anyone know where I find an 85 fuel sensor, I don't mind paying shipping to Europe, it's very light and won't cost much!

Thanks in advance, Matthew

"The fuel sensor tells the EFI unit if there is no fuel and shuts the engine down"

Are you sure?
Just looked at the wiring diagrams for all K100s and cant see how that works
or any obvious link between the sender and injection control system.

you have 4 wires to the tank. Power, Ground and in your case, two outputs to the warning lights
later bikes have 4 as well but only one to the low fuel warning light
and one ( yellow) which can be connected to a gauge.
In either case the power and ground wires supply the pump.
Perhaps the problem isnt the sender, but the supply to the pump?

I have been meaning to try here
Just been a bit lazy lately...They do all sorts of restoration and supply hard to find components.

reg_K100RS wrote:"The fuel sensor tells the EFI unit if there is no fuel and shuts the engine down"

Are you sure?
Just looked at the wiring diagrams for all K100s and cant see how that works
or any obvious link between the sender and injection control system.

you have 4 wires to the tank. Power, Ground and in your case, two outputs to the warning lights
later bikes have 4 as well but only one to the low fuel warning light
and one ( yellow) which can be connected to a gauge.
In either case the power and ground wires supply the pump.
Perhaps the problem isnt the sender, but the supply to the pump?

I don't know where I read this thing about the sender cutting out the EFI, I spoke to the "K" specialist, in the BMW agent I'm tryingto get the parts from, he said that the common earth , pump and warning lights was a possible problem. I went through thr trouble shooting k100troubleshooting looking for connections and references, couldn't find any, so mabe a direct feed to the pump is the test. Thanks for your thoughts I'll give it a try.

Hi Matthew and I know it sounds weird but a full time problem is vastly easier to fault find than an intermittent one, so if you wish to give us a bit more specific information we will be more than happy to throw some ideas your way.

The fuel sensor has no connections to the EFI.
The water temperature sensor will prevent the EFI to work if it sends a signal that the engine is over heated.
Can you disconnect the plug of the FI computer and measure what resistance you find between pin #10 and the ground (take the measurement at the plug with the ignition off) When the engine is cold, you should read between 1.5 to 2 K Ohms.

Matthew
To repeat Phils suggestion
A blow by blow description of the symptoms will
probably have these guys offering more detailed guesses of
what your problem really is.

I dont claim much expertise on these bikes but from what I can see
you could throw the senders away and the bikes would run fine
as its not a critical component, but an accessory.

I concur the fuel sender as Crazy Frog says has nothing to do with the EFI it would be illogical to build that in because if the bike is out of fuel it stops so there is no need to electronically stop the bike with a sensor for fuel level. As Bert says the temperature sensor will stop the bike starting but will allow the bike to run until you shut it off and will prevent a re-start until it has cooled. As the guys say above you need to give us the full symptoms you are experiencing, is it a no start from cold, a no start from hot, cutting out at idle or a shut down whilst you are riding? Once we have some facts to go on we can do some diagnosis. Also if the K specialist at the dealer told you the fuel level sensor was a problem you have just located someone who you should not rely on for diagnostic advice.
Regards,
K-BIKE

Hi,
I fed the fuel pump directly through the reservoir cap, eliminating possible bad connections in the fuel sensor. The pump worked normally, but the plugs are dry. I've printed out the "crazy Frog" trouble shooting doc. (Bertrand tu et en France j'imagine, je suis a Aubervilliers dans le 93. Je cherche pas a t'emereder, just eventuellement profiter de tes connaiscance des fournisseurs ouvert en ete!) It's time to start testing seriously with the multi meter!

Regards, Matthew

mattinker@yahoo.com

I am sorry but I am not in France. I am living on the East coast of Canada (but I am originally from France). I don't have any idea of which dealer is open during the summer in your area.
The EFI troubleshooting has been updated in English, but not in French (sorry but I don't have the time. Maybe next winter). Please look at both versions to get the maximum of info.
Can you please tell us if you get power at the fuel injectors.
This will give us some clues to help you troubleshoot your problem.
If you have any language problem (I don't think you do) send me an MP.

Bert

Bert,

thanks for your reply, I should have looked on the right hand side of your message to see where you live! I have no problems with English, it's my mother tounge I've only been massacering the "langue de Moliere" for thirty years!

I'll try and get onto the injector current test tonight, reading through your troubleshooting guide, it certainly seems like the place to start!

Regards, Matthew

I massacre the langue of Shakespeare for 20 years and proudly speak Frenglish.

I know enough 'Franglais' to make myself misunderstood in
both languages

Moving slowly forward, 12volt LEDs should arrive tomorrow,so with any luck I'll be able to test the fuel injector supply.

Matthew (who's using his bicyle far too much these days!)

Hi,
my 12 volt LED arrived, tested for current at the injectors, nothing. Fuses are all OK, the fuel pump functions normally when fed directlyfrom it's supply without going through the sensor. So what next? This fault has been intermittent, getting worse, The bike would ocassionally cut out, either for a second or two, or for much longer, pulling on varous bits of the loom seemed to get it going again. I cleaned the earth connections, all of the cable connectors, the battery earth. After the clean up I thought I had it licked, but a week later, it started again. After the latest fuel sender episode, where both fuel lights came on with a nearly full tank it's not even trying to start,wheras before, it would fire two or three times and stop. Now, the plugs are clean and dry.

I would very much apreciate help with the next steps, I trained as a mechanic brfore the arrival of electronic injection. I have no problems with the mechanical side, but the electronics! I can use an ohm meter, I'm an indusrtial electricien also, but no electronics! Regards, Matthew

Just a wild guess but how about the throttle position switch?
(black connector on LH side at rear of fuel rail)
if it sends a 'closed' signal to the efi thingy no fuel is injected
I and I know others have had problems with these

I guess the next easy step would be to test the water temperature sensor.
The easiest is to unplug the EFI computer and measure the resistance between pin #10 of the plug and the ground.
Here is the values you should read. When the engine is cold (water between 20 and 30 degrees), the resistance should not be under 1.5 kΩ

Hi, I tried starting with the throtle switch dis-connected, nothing changed. I've allready changed the water temperature sensor twelve months ago. It would start even when it was bad, it was treating it as though the engine was hot, I'm getting nothing at the injector out put leads!

Regards, Matthew

Matthew,

Even if you had replaced the water temperature sensor, it could fail again. If it is shorted , the bike WILL NOT start.
You told us that the plugs are dry, but.... do you have spark at the plugs?

If the EFI doesn't receive a signal from the ignition unit, it will not power the injectors.

You tested the signal at the injectors and got nothing. Do you get at least +12v at the injectors?
- Set up your multimeter for 12 volt DC
- Unplug the electrical connector of one injector.
- put the positive wire of your multimeter to the connection fed by the Green/red wire.
- touch the engine with the other wire of your multimeter (need to be a good ground)
- Turn ON the ignition and crank the engine.
You should read 12v.

Bert

My '87 had the same problem...turns out the fan motor was toast and causing a loopback through the sensor, shutting down the fuel pump relay. Replaced the fan motor and she ran right as rain.

Thank you all for your help so far, I am so short of time at the moment, that I bought very cheaply, with a friend a K75 (ex police) to use whilst I get through this work crisis period, I'll get back to the K100 later! So I'll be back again I should think! Thanks again, Matthew