K100RS running rich

[thormeyer]

Hi All..

I'm new the forum an to the brick. I bought a 1985 RS with only 9500 orig. km on it!!!!  :euro But as I drove it back home I found it had very bad fuel economy (about 26 mpg (10,5 km/l)). I pulled the plugs and they were all back. I have read alot about this on the forum abput runing rich and the first i did was to take off the radiator, termostat and temp. sensor for the ECU box.

The termostat work fine, but the rubber was in bad condition - bought a new.
The temp. sensor work fine - bought a new to test against.

So new the head scratching began!! But then I came across the topic on the forum (http://www.motobrick.com/index.php?topic=3509.0) were Inge K. suggests to check the wiring from temp. sensor til ECU (L-jetronic). I did this and found the resistance was much higher when I messured at the big connecter!!! So even when I drop the temp. sensor into 100 degree celsius water the resistance do's not come under 5 kOhm.. Which will make the L-jetronic think the bike is about 4 degrees all the time - ergo rich fuel mix!!

Now comes My real question - How do I fixit??? Can I buy the a new wire loom?? Is it better to repair?? The wire loom from the L-jetronic has alot of other wires goning in and out, so i not sure I would do it my self, even though I have work on many bikes before (mostly 70's honda, bmw, moto guzzi - wiring not to complex)

Hope some one has a good idea..


Best regards

Thor Meyer
Denmark
   

[Laitch]

But then I came across the topic on the forum (http://www.motobrick.com/index.php?topic=3509.0) were Inge K. suggests to check the wiring from temp. sensor til ECU (L-jetronic). I did this and found the resistance was much higher when I messured at the big connecter!!! So even when I drop the temp. sensor into 100 degree celsius water the resistance do's not come under 5 kOhm.. Which will make the L-jetronic think the bike is about 4 degrees all the time - ergo rich fuel mix!!

Did you perform the test on the new sensor, too, Thor,  or only on the original sensor installed on the bike?

[thormeyer]

Hi Laitch

Yep - I did the test on both. Same results.

/Thor

[kennybobby]

Check the ground connections at the bolt located under the fuel tank--remove the bolt and clean all the lugs.  That is where pin 13 makes it's path to ground, and if it is corroded it will result in a higher resistance reading such as you have measured.

Also pull the cover off of your ignition coils and try to start it at night--if you haven't replaced your ignition wires recently then you may observe a little lightning storm around the boots and wires.  When the condition gets really bad it will feel like bogging and lack of power when riding and also cause poor fuel economy.  kb

[Laitch]

Checking ground connections, as kennybobby suggests is alway good practice.

Why is the new sensor not giving the correct values? A correctly functioning sensor should follow the resistance arc on this graph if the test is being performed correctly and the measuring device is accurate, so it is premature to consider at the loom at this point, I think.

[thormeyer]

OK kenneybobby - i have pull the wiring out so it is more easy to see the wire and test. I will try to ground the brun wires again, after i have cleaned the surface on the ring terminal on the the wires and the connection point.

Laitach - when i connect the old and new sensor direct to the multimeter an put it in boiling water, the sensors follow the curves, but when I connect the sensor to the loom and messure with the multimeter af the L-jetronic plug, I messure about dobble the resistance.

/Thor
 

[The Mighty Gryphon]

It sounds like you have found the problem and it is in the wiring between the sensor and the L-Jetronic.

First thing I would do is to check the wiring continuity between the sensor and the points the wiring connects it to.  This is to see which of the two wires is the bad one.  I would also get some DeOxit contact cleaner and give the plug at the sensor end a good shot.  This connector is in a spot where it can see a lt of water, dirt and salt.  The connector at the engine control unit is much more protected and less likely to be the source of the problem. 

If still bad, try to follow the wires through the bike and see if you can find any breaks or spots where the insulation has been damaged.

Last, you can measure resistance through the wire by carefully sticking a pin through the insulation and into the wire and connecting the meter to it.  This way you can test the connection between the connector pin and the wire itself.

[thormeyer]

I hope so.. Hope it is a bad ground connection. But yes I will do some fiddling and mesuring.  :2thumbup:

And if it is the wire then i think i will take to a professional auto electrician, so I is done right.. Is it still possible to buy the plugs/connectors??

/Thor

 

[kennybobby]

Howdy Thor,

Really simple to check the wiring resistance.  Measure from Pin 10 of jetronic connector to the socket connector at the sensor--this checks just the signal wire.

Then to check the ground, measure from pin 13 of jetronic to the engine case.  My bet is that this is where the high resistance will be found.

[The Mighty Gryphon]

How do the terminals on the sensor and it's connector on the harness look?  Do they show any corrosion?

[thormeyer]

Hi Kennybobby,

Yeah - I pulled the wire diagram and can see the other pind goes to the temperature sensing unit. So one pind to the J-tronic and the other one to the temp. unit. So I need to check all ground connections to be sure - especially the connection from the temp. sensor and back.

Yeah - i think your right. The wire all seem in very good condition.

Mighty Cryphon - they all look to be in very good condition..

/Thor 

[rbm]

The temp sensor grounds through the stand pipe.  It is common that corrosion at this threaded connection can introduce more resistance in the circuit. Also, sometimes people use PTFE tape on the threads --don't do that. Make sure the threads on the temp sensor and the stand pipe are clean and conductivity is as good as it can get.

[thormeyer]

Hi rbm..

Yep - I will clean all the ground connections on the bike and messure the resistance at all the ground points, to be sure.

by the way - should I get the injectors cleaned?? The bike only has 9500 orig. kilometers on her (that's an average of 300 km a year). So my guess is the bike has stood still for many years, which is not good for the injectors.

/Thor

[thormeyer]

Hi all..

Small update - I have been working on the bike today. I have dobble checked the wiring loom and after discovering that the temp. sensor need to have ground, there was nothing wrong with the loom... Hmmm.. BUT..

Now I moved on to the TPS, which I have read also can have a effect on rich running if not adjusted correct. This is what i found:

- There was no "click" when I moved the throttle - put the multimeter on (messuring ohm). With the throttle closed there was no resistance and with throttle open the same reading (had the multimeter on the common/ground pind and the one furthest out.

-Now I put the multimeter on the common/ground and the one furthest in - I messure no resistance with closed throttle, and about 2 ohm with full open.

So I took the TPS off, cleaned it and gave it some lubrication, put it back on and adjusted it, as described on a forum post.

Now it clicks and there is and resiatnce when the throttle is closed and none when I open (on the furthest out) and on the furthest in, no resistance when throttle open and about 2 ohm when full open..   

IS THIS RIGHT????...

Also does any one now how the vacuum switch works and what it is for???


/Thor
 


 

[Laitch]

Now it clicks and there is and resiatnce when the throttle is closed and none when I open (on the furthest out) and on the furthest in, no resistance when throttle open and about 2 ohm when full open..   IS THIS RIGHT????...
Also does any one now how the vacuum switch works and what it is for???

If I were at this point in diagnosis and treatment, Thor, I'd be taking the bike out for a run to see how it responds and to check the spark plug insulator firing tip color.

The purpose of the vacuum switch (highlighted in red here) is described in Vogel's troubleshooting guide section about the throttle sensor like this:
With this system, when decelerating (switch 1 close), the fuel injection is disabled until the rpm goes down to 2000rpm. If the engine is still decelerating and the rpm is lower than 2000, the EFI is re-enabled and the injection is controlled again by the FI computer. As an example, when riding at 5000rpm and cutting the throttle, the injection will be cut off between 5000 and 2000rpm. (This is one of the reason why the K100 really slow down when you shut down the throttle.) This switch assembly only signals idle or full throttle to the EFI. Mid throttle signal to the EFI was controlled by the vacuum switch. This switch has been removed in the late 1985)

[thormeyer]

Hey All..

I'm having a bit of problems with my BMW K100 from 1985. It was running rich and i have know checked and replaced:

- Fuel regulator
- Water temp sensor
- Thermostat
- Sparkplugs
- Oil and filter
- Checked the wiring and resistance
- Air Filter

But it is still running very rich - balck smoke when I rev and the exhuast smells of fuel.

I have made a small video of how it sounds - https://www.dropbox.com/sh/jkanleimg3ce506/AAClfmFIl2eDsCZl-WHJeZXaa?dl=0

I have just received a fuel pressure test kit and will test the fuel pressure - to be sure it is just right.

Hope some one has a good idea...   

/Thor Meyer

[bikesnbones]

It might also be worth changing the air filter.
If that's filthy and clogged, it could cause rich running.
What were the condition of the spark plugs (colour)

[thormeyer]

The filter is also new (forgot to write it).

the old plugs were black - I put new Bosch plugs today (just put the bike together today after replacing all the obvious, but still running rich, as seen on the video)

/Thor

[thormeyer]

I have one more question  - should the rpm rise if I pull of the small black vaccum plugs on the throttle body??

/Thor

[kennybobby]

It will with your bike since you are running rich, the extra air drawn in thru the vacuum port will cause the rpm to increase.  On a bike with a normal mixture it would cause a lean condition and stalling.

You will need to check all the sensors to find out which is out of spec.  For example, check the  engine water temperature sensor resistance between the jetronic connector socket pin 10 and the ground lug--should be ~2.5kOhms at 20C.  If it is reading significantly higher, or open circuit, then it will cause the jetronic to enrichen the mixture.

[Laitch]

Also, here are a couple of relevant posts in threads dealing with rich mixtures, Thor.

http://www.motobrick.com/index.php/topic,7800.msg55850.html#msg55850

http://www.motobrick.com/index.php/topic,3509.msg21098.html#msg21098

[thormeyer]

Hey Laitch..

I have had the bike started yesterday - unfortunately no improvement.. :( (here a small video of it running: https://www.dropbox.com/sh/jkanleimg3ce506/AAClfmFIl2eDsCZl-WHJeZXaa?dl=0) She's still running VERY rich.. I pulled out the small black vaccum plugs and the rpm raised, which for me indicate to much fuel.

I'm running out of things to check - I will check the fuel pressure in the rail, to be sure it is spot on. If this is this case I think I will take of the injectors and have them tested/reconditioned.

Any other good idea's???

/Thor 

[thormeyer]

Hey All..

I did a pressure test on the fuel system today - The pressure was way to high - over 70 PSI!!! The pressure regulator is all new, so it should not be there the problem is.

was else could cause this high pressure in the system?? I'm thinken a clog in the return?? does this seem plausible??

best regards

Thor

[kennybobby]

When you measured the 70 psi fuel pressure, was it with a tee in the line to the fuel rail?  That is the pump pressure when deadheaded--sounds like the regulator is not flowing.

You could pull the return line from the front of the tank and run it into a bucket to check that the regulator is open.

[rbm]

That pressure is nearly double, probably full pump pressure so the regulator is not working.  Possible causes could the a defective regulator from new, improper vacuum hookup to the fourth throttle body, maybe clogged return.

When the engine is running, open the lid on the tank and  look inside.  You should see ripples in the content indicating that the fuel is returning to the tank.  A blocked return will have a very noticeable effect on this return stream.

If you decide to replace the regulator (again), then there is a good variable one that allows you to set the pressure. Search Ebay for 231581166056.