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Discussion Starter #1
Hi all I have an annoying new problem with my 1985 k75, this surfaced after running out of fuel on my way home after a long week at work when I was just looking forward to getting home without problems! I pushed the bike the last few hundred yards to the gas station, refueled but the bike but it refused to start. I can now hear the fuel pump has stopped working but first removed the fuel pipe connected to the injector rail to try to suck fuel through to remove air and prime the system but no fuel came through even when cranking the engine. Is this likely to be the pump fuse or are pumps prone to damage if the engine is cranked without fuel ? Thanks in advance guys Selly
 

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PsyKotic Waterfowl
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It shouldn't die just because you ran out of gas.

That said, the fuel pump is cooled by the gas around it so it's probably not a good idea to run it way low all of the time.

There's no need to prime things when you run out of gas.

I'd pull the pump out and bench test it to see if you hear it spinning. (The smaller diameter terminal is positive.) Or you could jump it in the tank - just be careful not to make any sparks in the tank for obvious reasons.
 

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+1 on the fuel being your pumps only coolant and it is designed to be immersed during operation. Engine cranking has no relevance to the electric fuel pump's operation, so if you can't hear the pump come up to pressure before touching the starter, it's either toast or not getting juice. You'll be very fortunate if it's just a fuse or failed wiring, that pump is far from new being an 85, so I fear the worst and expect you are looking at a new pump (and filter while you're in there) On the bright side, if you do replace it you should be good for another 25 years ;)
 

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PsyKotic Waterfowl
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TrialsRider said:
+1 on the fuel being your pumps only coolant and it is designed to be immersed during operation. Engine cranking has no relevance to the electric fuel pump's operation, so if you can't hear the pump come up to pressure before touching the starter, it's either toast or not getting juice. You'll be very fortunate if it's just a fuse or failed wiring, that pump is far from new being an 85, so I fear the worst and expect you are looking at a new pump (and filter while you're in there) On the bright side, if you do replace it you should be good for another 25 years ;)
This is not true for a 1985 K100. Two valve K bikes don't start the fuel pump until the starter button is pushed. Four valve K bikes pre-pressurize the fuel system for a second or two when the key is turned on.
 

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FlyingDuck said:
This is not true for a 1985 K100. Two valve K bikes don't start the fuel pump until the starter button is pushed. Four valve K bikes pre-pressurize the fuel system for a second or two when the key is turned on.
+1 on the pump not starting up until the starter button is hit. The ignition control module appears to activate the fuel injection relay (by schematic.) I would have to say the ignition control module is either looking for the start button input to activate circuits for the FI control relay, or it is looking for the Hall Sensor activation to determine the need for the fuel pump. This is probably because these bikes do not run an electronic feedback fuel pressure regulator (vacuum controlled on early bikes) so the fuel injection controller and ignition controller will not be able to see what fuel pressure it has in the system. Also, you will notice this is a return system fuel injection system, not a dead head system, thus the nice warm fuel tank on cold days and hot tank on hot days. So un-used fuel is returned to the fuel tank via the return line. This makes air locks a lot more difficult to happen.

I would check the ground to the tank (brown wire in the fuel tank harness connector located on the right side of the bike behind the right side cover.) Also check the green and white wire for power in the same connector. Make sure you check both of these on the frame side connector and not the connector that goes up to the tank. If you have power then more than likely the #1 and #6 fuses are okay. BUT......CHECK the condition of the fuses anyway. Even try substituting in new fuses anyway. (Should always have extras in the bike for safety anyway. A box of extras saved another riders bacon in the high mountain desert outside of John Day,Oregon thanks to my foresight to have them. He was grateful due to not wanting to walk 25 miles in 102F to get a tow. They do just get old and go bad after years of on and off use. As well, the contacts in the Fuse Panel are somewhat exposed to the weather and can corrode.) If you know how to check a relay for proper activation and control I would check the FI Control relay as well.

Good Luck and Safe Riding
 

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FlyingDuck said:
This is not true for a 1985 K100. Two valve K bikes don't start the fuel pump until the starter button is pushed. Four valve K bikes pre-pressurize the fuel system for a second or two when the key is turned on.
Curious, you can certainly hear mine wind up for about 2 seconds when the key is turned on (86 K100RS) and if the battery is too flat I can't even bump start it down a big hill. Sorry if I steered you wrong Selly and do let us know how it turns out.
 

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Discussion Starter #7
Solution found

Hi all thanks for all of your responses. The pump problem turned out to be down to a blown fuse which I missed when I checked them in the dark with an obviously inadequate flashlight. Lesson learnt - now I have a decent flashlight and a few other useful things packed on the bike ready for minor repairs. Selly
 

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why

Why'd the fuse blow?
 
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