BMW K bikes (Bricks)

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Bikelord

Bikelord
active member
active member
Hi again everyone! 

A bit of a technical question for you all. I'm currently building a K100 cafe racer up from scratch using a m.unit and stripping all the unnecessary electronics out.

I'm really close to having the bike complete, but I'm currently running into an issue.
Currently the bike will only start and idle with the fuel pump disconnected.

I have tested the fuel pump, it pumps fuel in the correct direction and flows fuel through the front of the rail towards the back of the rail, through the FPR and then back into the tank. The injectors all seem to be functional all squirting as they should, spark plugs are all working sparking as they should, and compression is normal.

I've checked the alternator and it is charging the bike at 13.7 volts when it is idling.

When the bike has the fuel pump connected and you attempt to start the bike it will continue to crank and will struggle to start. as soon as you disconnect the pump the bike will fire up instantly, and idle normally.

I then went and tested the system by plugging the pump into a external power supply, and as soon as I connected the pump with the bike idling, the bike instantly chugged and shut down. Similarly when the bike is idling and the pump is plugged into the bikes connector, the bike will instantly start chugging and shut down.

So the question is, why would the bike be only able to start and run with the fuel pump disconnected? Could the issue be with the Fuel Pressure Regulator or something else I'm overlooking? 
On the odd occasion that I have been able to get the bike to run with the fuel pump connected, it will only run briefly and very roughly, any advice would be greatly appreciated!


Cheers!!


__________________________________________________
BMW K100RT 1987
BMW K100rt 1987 White Ex-Police (CHiPs)
    

duck

duck
Life time member
Life time member
My first guess, as you pointed out, would be a bad fuel pressure regulator.

The Bosch part # is 0280130069 - which costs a lot less than the same part with a BMW part #.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

duck

duck
Life time member
Life time member
Another possible source of overfueling is the temp sensor on the coolant pipe coming from the cylinder head.  If that temp sensor is bad or disconnected then the engine will flood quickly and die.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

MartinW

MartinW
Life time member
Life time member
+1 on Duck. However due to the location of the switch it is subject to water and road crap. This can lead to a bad connection which needs to be cleaned with something like 2 part DeoxIT. As and extra precaution I smear dielectric or heavy silicone grease around the connection. The theory being the grease with keep out water and air that leads to corrosion and a bad connection. I've had problems twice with this connection until I pulled it apart and cleaned it properly and greased it.

Merry Christmas regards Martin.


__________________________________________________
K75s Hybrid
    

Bikelord

Bikelord
active member
active member
@duck wrote:Another possible source of overfueling is the temp sensor on the coolant pipe coming from the cylinder head.  If that temp sensor is bad or disconnected then the engine will flood quickly and die.
Interesting you should say that the temp sensor might be the issue. As I mentioned earlier I've pretty much gone through the electronics and removed some of the unnecessary stuff, in the process I haven't gotten around to fitting a coolant light indicator, is the coolant light 100% necessary to run the bike?
All the wiring for the coolant temp sensor is still in tact, just minus the indicator light bulb.

Also that part number you've graciously provided is a for a coolant temp sensor, which I will most likely need now, hahaha. But if I was after a replacement Fuel Pressure Regulator, what would be the part number for a suitable bosh equivalent?


__________________________________________________
BMW K100RT 1987
BMW K100rt 1987 White Ex-Police (CHiPs)
    

Bikelord

Bikelord
active member
active member
@MartinW wrote:+1 on Duck. However due to the location of the switch it is subject to water and road crap. This can lead to a bad connection which needs to be cleaned with something like 2 part DeoxIT. As and extra precaution I smear dielectric or heavy silicone grease around the connection. The theory being the grease with keep out water and air that leads to corrosion and a bad connection. I've had problems twice with this connection until I pulled it apart and cleaned it properly and greased it.

Merry Christmas regards Martin.
Good to know! I'll be sure to check the Temp Sensor wiring and contacts next time I'm working on the bike. Just out of curiosity, when you say you've had issues with this connection before, what are the symptoms you have experienced?

Merry Christmas!


__________________________________________________
BMW K100RT 1987
BMW K100rt 1987 White Ex-Police (CHiPs)
    

mike d

avatar
Life time member
Life time member
If you've not done so already then go to the tech pages http://www.kforum-tech.com/

and in the electrical section read the 'Troubleshooting the EFI' It will show how to measure the temperature sensor resistance which will tell if it is working correctly or not.

The 'coolant light' is a separate item as it only illuminates when the engine is over temperature. If the the bike is running when the bulb illuminates the bike will continue to run. However if you turn off the engine, you will not be able to restart it until the light has extinguished (i.e. the temperature is below the cut off point).

Mike

    

duck

duck
Life time member
Life time member
@Bikelord wrote:
@MartinW wrote:+1 on Duck. However due to the location of the switch it is subject to water and road crap. This can lead to a bad connection which needs to be cleaned with something like 2 part DeoxIT. As and extra precaution I smear dielectric or heavy silicone grease around the connection. The theory being the grease with keep out water and air that leads to corrosion and a bad connection. I've had problems twice with this connection until I pulled it apart and cleaned it properly and greased it.

Merry Christmas regards Martin.
Good to know! I'll be sure to check the Temp Sensor wiring and contacts next time I'm working on the bike. Just out of curiosity, when you say you've had issues with this connection before, what are the symptoms you have experienced?

Merry Christmas!
On my K100 the connector for the temp sensor just came loose and fell off.  Must have been from a prior person doing sloppy maintenance because it has a sturdy wire clip on it that won't just fall off.

The symptom I experienced is that it just quit from flooding and then it was overfueling so much that when I tried to start it gas dripped onto the ground from the connection between the headers and the exhaust can.  My bike has an aftermarket exhaust though so I'm not sure if a bike with a stock exhaust can would drip like mine did. (The bike has a Luftmeister exhaust.)


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

Laitch

Laitch
Life time member
Life time member
@Bikelord wrote:I'm really close to having the bike complete, but I'm currently running into an issue.
Currently the bike will only start and idle with the fuel pump disconnected.
At this point, I'd welcome an explanation of how an engine that depends upon fuel pressure to operate can operate at all without fuel pressure, which is what is being asserted here.

How long will it "idle normally?" The engine should not run if the fuel pump isn't running, too. Review what you are disconnecting and connecting. It seems to me you might have delivery and return hoses and wiring connected incorrectly or misidentified regardless of your assertion to the contrary. Check the fuel pressure vacuum line for fuel.

Check all your tank fuel line connections for tightness. Be certain your fuel filter isn't clogged.

If you can get the engine to rev under load without a fuel pump, this will be a giant stride in the search for fuel economy. Smile


__________________________________________________
1995 K75 81,000 miles
Fueling Issue? Whats your best guess? Usa-lo10
    

MartinW

MartinW
Life time member
Life time member
On the two times my temperature sensor connection failed I had the following symptoms. Bike would crank over as normal but failed to fire up. You could smell fuel coming from the exhaust. On removing the plugs they were extremely wet. After drying the plugs and very carefully checking spark was present (do not set fire to your bike when doing this), I came to the following temporary solution to get myself home. I removed the fuel pump fuse #6 marked Kraftstoppe a and let the cylinders and plugs dry out for about 30 min. I was going to crank it over but was afraid my bike might of self immolated. After drying out refitted the plugs and tried to start the bike after a couple of coughs and splutters and throttle manipulation it started and ran albeit very rough. As the residual fuel ran out it started to die so I jammed the fuel pump fuse back in and by manipulating the throttle I managed to keep it running. The second time it happened I managed to get my hand in the wriggle the connection but when that didn't work I went back to the first method and pulled the fuse. There is a second method employed by .75 which involves unplugging the fuel pump in stead of removing the fuse. Due to the fact that this connection can be a source of problems on Bricks I tended to avoid playing with it.
Regards Martin.


__________________________________________________
K75s Hybrid
    

Bikelord

Bikelord
active member
active member
@Laitch wrote:
@Bikelord wrote:I'm really close to having the bike complete, but I'm currently running into an issue.
Currently the bike will only start and idle with the fuel pump disconnected.
At this point, I'd welcome an explanation of how an engine that depends upon fuel pressure to operate can operate at all without fuel pressure, which is what is being asserted here.

How long will it "idle normally?" The engine should not run if the fuel pump isn't running, too. Review what you are disconnecting and connecting. It seems to me you might have delivery and return hoses and wiring connected incorrectly or misidentified regardless of your assertion to the contrary. Check the fuel pressure vacuum line for fuel.

Check all your tank fuel line connections for tightness. Be certain your fuel filter isn't clogged.

If you can get the engine to rev under load without a fuel pump, this will be a giant stride in the search for fuel economy. Smile
That's exactly what I thought, there is no way the bike could run without pump pressure! However here we are I have a k100 that runs without it (somewhat). Of course it only really idles I haven't really been too game to run it for too long without it connected, but I have had it going for about 1-2 mins without the pump. My best guess is that the intake stroke draws some fuel through, enough to let it idle? Out of curiosity when the fuel line is pinched from the tank to the rail, the engine starves. Also when the bike is rev'ed without the pump it will stumble, like it is being starved.

I am 100% without a shadow of doubt, certain that the direction of the travel is correct. 

I.E. from the pump, to the filter, out the tank, through the rail, to the pressure regulator and back into the tank.

Similarly I have quadruple checked that the wiring is correct using wiring diagrams, making sure the polarity is correct on the pump, so it pumps fuel in the correct direction. I've checked all the fuel lines replacing all of the old and hard ones for fresh fuel lines. Same goes for the vacuum hose to the bottom of the regulator, it visually looks fine and created a vacuum on the receiving end of the hose.

I'll check the filter again, but it does get flow through it when testing the pump as the return line has adequate flow coming out.

At this point it seems as if the FPR or Coolant Temp Sensor/connection is the culprit.

LOL, I wouldn't complain about having the worlds most efficient K100, but only if it ran. Hahaha!

Cheers, Ken.


__________________________________________________
BMW K100RT 1987
BMW K100rt 1987 White Ex-Police (CHiPs)
    

Laitch

Laitch
Life time member
Life time member
@Bikelord wrote:
That's exactly what I thought, there is no way the bike could run without pump pressure! However here we are I have a k100 that runs without it (somewhat).
Brilliant.


__________________________________________________
1995 K75 81,000 miles
Fueling Issue? Whats your best guess? Usa-lo10
    

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