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Enjoy The Ride
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Discussion Starter #1
My bike is running so bad it starts to foul a new set of plugs in less than 50 miles. the fuel milage has gone from the low 50s mpg to the mid 20s mpg. It had been at the dealer for almost six weeks & they are stumped. I just can't give them a blank check & have them fix it.

The only fault code is the O2 sensor. 2 different sensors have been installed & both still showed a fault code. They also checked the injectors for leakage. They changed the Motronic control unit & Ign. coil. Nothing helped. The way the bike runs its more than just dumping to much fuel. It barley has enough power to get going from a stop light.

I do have have a good Digital Multimeter but I'm not very good with electronics. The mechanical part of the engine (valve lash,compression test & leak down) is the same as it has been for the last 30,000 miles.

If there is any interest in the Charlotte NC area for a tech session I would be more than happy to have one. I have plenty of space & all the tools that would be needed.

Any thoughts: Thanks Dave
 

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Enjoy The Ride
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Discussion Starter #3
mobygrape said:
Engine temperature sensor?
It runs the same hot or cold. It also started out as a intermittent problem but now is a full time problem
 

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Fuel pressure regulator? Too much fuel spraying through the injectors may cause the 02 sensor to be confused.
 

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Discussion Starter #5
pushin9s said:
Fuel pressure regulator? Too much fuel spraying through the injectors may cause the 02 sensor to be confused.
When I checked the fuel pressure it was 65 to 80 lbs & that was the first thing I changed. At first first I was sure that was the problem. With the new regulator it is now a steady 50psi.
 

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2005 K1200LT
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You say two O2 sensors have been installed and they both read faults? Get out your meter and check that there is 12V at pin 1 of the connector (should be green/white on the bike side harness) This is fed from the fuel pump relay so the bike should be running when you test it.

The only other thing is to check continuity from the O2 sensor connector to the Motronic. Sounds like everything else has been eliminated.

pin 1 Green/White fed 12v by Fuel pump Relay
pin 2 Green/Brown to pin 25 at Motronic
pin 3 Yellow to pin 12 at Motronic
pin 4 Black to pin 11 at Motronic.

Note: the last two are also sheilded.

Good luck.
 

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If the engine temp sensor is bad, it can produce the extreme rich condition that you describe. It won't matter if the bike is hot or cold, it will be way to rich to run in any condition. The O2 sensor problem might cause poor milage, but not the plug fouling and driveablity problems that you describe. I had an oilhead that had an intermittent excessive richness fault. It would go from running fine to barely able to make it home. It was the engine temp sensor.
 

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Good point Paul. It is the one on the rear of the cylinder head.
 

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I would think that if two O2 sensors are showing a fault code in the computer then there is a good chance of a short circuit or open circuit in the wiring harness between the O2 sensor and computer. This would cause a full rich condition.
 

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Discussion Starter #10
mobygrape said:
If the engine temp sensor is bad, it can produce the extreme rich condition that you describe. It won't matter if the bike is hot or cold, it will be way to rich to run in any condition. The O2 sensor problem might cause poor milage, but not the plug fouling and driveablity problems that you describe. I had an oilhead that had an intermittent excessive richness fault. It would go from running fine to barely able to make it home. It was the engine temp sensor.
If the engine temp sensor is bad would the temp gauge still work properly?. It is running worse than just a open loop O2 sensor.
 

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Discussion Starter #11
jzeiler said:
You say two O2 sensors have been installed and they both read faults? Get out your meter and check that there is 12V at pin 1 of the connector (should be green/white on the bike side harness) This is fed from the fuel pump relay so the bike should be running when you test it.

The only other thing is to check continuity from the O2 sensor connector to the Motronic. Sounds like everything else has been eliminated.

pin 1 Green/White fed 12v by Fuel pump Relay
pin 2 Green/Brown to pin 25 at Motronic
pin 3 Yellow to pin 12 at Motronic
pin 4 Black to pin 11 at Motronic.

Note: the last two are also sheilded.

Good luck.
I will check the voltage as soon as I get the tank back on. My wiring diagram doesn't show where the volts come from. I still need to remove the upper fairing. I want to be able to look at the whole wiring harness. There is visible signs of salt spray from riding this past winter under the gas tank.
 

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saddle-man said:
If the engine temp sensor is bad would the temp gauge still work properly?. It is running worse than just a open loop O2 sensor.
There are two temp sensors. The one that feeds the guage is on the water pump, the one that feeds the Motronic brain is on the back side of the cylinder head near the coil pack.
 

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I had a similar problem and the falt was due to a defective Throttle Valve Stub . The shop manual refers to this as the Throttle valve potentiometer.
This does not support the prior DX code of faulty O2 sensor, Just some food for thought.
 

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Discussion Starter #14
The continuity of the O2 sensor checks out on the three wires to the computer. The green-white wire has 13.72 volts when running.
On the engine temp sensor is it possible to put it in a pot of water & bring it to a boil while checking the ohms?.
 

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You could but there is no data available on what the correct readings should be. If it is working I would expect a change in reading as the temp increases. If you don't get a change I would say it is bad.

I would say just change it but it, like every thing else, is an $80.00 part.

Also since the cable is relativley short you may be able to just disconnect it and see if there is a difference in the performance.
 

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Enjoy The Ride
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Discussion Starter #16
I just checked the engine temp sensor with the engine cold. On the 4k scale it reads 1.993 & on the 4m scale it reads .002. I said I have a nice Digital Multimeter but I didn't say I know how to use it. Not knowing wich scale to use I'll check both.

I just put another set of spark plugs in they shouldn't foul near as quick with no load. I'll run the engine at a fast idle & watch the ohm meter on the engine temp sensor as the engine heats up. I'm not ready to just throw parts at it yet.
 

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I had a 2000LT that did the same thing. Limped into the dealer. The dealer had the bike for 16 weeks and could find nothing diagnosable. BMWNA was no help. Finally replaced the Motronic unit. This fixed the problem for a short while. I finally tore into the bike and found a number of electrical connections showing corosion. I cleaned them up and gave them a coat of di-electric grease. This permanently solved my problem. Hope this helps.
Chris
 

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Discussion Starter #18
cbrxman said:
I had a 2000LT that did the same thing. Limped into the dealer. The dealer had the bike for 16 weeks and could find nothing diagnosable. BMWNA was no help. Finally replaced the Motronic unit. This fixed the problem for a short while. I finally tore into the bike and found a number of electrical connections showing corosion. I cleaned them up and gave them a coat of di-electric grease. This permanently solved my problem. Hope this helps.
Chris
The dealer tried a motronic with no help. The only corrosion I have found so far was with the BC computer connections which the mechanic said was normal. That has been unhooked for the last 2000 miles. I have my radar detector in its place.
 

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Discussion Starter #19
It won't run but for a few seconds with the engine temp sensor unhooked. I just hooked the temp sensor back up & ran it until the water temp reached 220 at the radiator thats when the fans kicked in. The 4k reading cold was 1.993 at 220 its at .170. The 4m reading cold was .002 at 220 its at .000.

For its worth I also checked the exhaust temps at the header flange. #1 490, #2 406, #3 350, #4 350

I'm leaning towards the temp sensor is ok.

Now that the bike is to hot to work on I'm headed out back to my 32,000 acre heated swimming hole for a dip. :cool:
 

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I have to agree the sensor sounds fine. This is going to be a tought one but I'll hang in there with ya on it.
 
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