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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: fourwinds on April 23, 2015, 09:34:48 PM
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87 k100 RT, intermittent fuel pump operation.
To summarize,
When ignition key is on, one can hear the fuel pump running.
Bike starts and runs for perhaps 3-5 sec.
After engine stops, the fuel pump can be clearly heard to RE-start. (this tells me that it had stopped at some point.)
A wire run from the battery positive terminal to the fuel pump fuse slot results in the Fuel Pump running constantly, bike starts, revs, runs well. Let it run long enough to warm up and test that the fan operates.
Have gone through the diagnostics on:
Air flow meter, temp switch, basic FI operation.
I suspect the Fuel Injection Relay is at fault.
Does that sound correct?
Thanks to you all, the info I have found here has already been of great assistance!
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Dirty contacts on the FI controller would be something to clean/check to rule out.
You can swap the FP relay with another one to rule out the relay.
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Additional info:
Pulled out FI relay, applied power, it "clicks"
Installed FI relay, checked for power at Fuse #6, nothing while pressing starter button.
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Additional info:
Pulled out FI relay, applied power, it "clicks"
Installed FI relay, checked for power at Fuse #6, nothing while pressing starter button.
Just because you can hear an audible "click" is no guarantee that it will pass current to drive the pump..........
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after peaking into the tank to verify i gotts enough fuel to fire this thing off and sustain normal operation... id be looking at the under tank wiring harness connector... thats after i replaced the fuel filter of course... and after i preformed the backspin starter maintenance...
butts thats just me... one lonely motobricker with recycled air in my tiors...
j o
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The fuel filter & lines are all new. Plenty of gas. The 4-wire connector under the tank tests good.
Fuel pump can be heard running with ignition key on, before pressing starter button.
Starts & runs for a few seconds, then engine dies. Fuel pump clearly RE-starts.
As a test, I put her all back together, jump a wire from positive terminal of battery to the left side of the #6 fuse, and she'll run all day.
The puzzle is this: what is causing the fuel pump to stop running during the starter engagement cycle?
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Did a bit more testing at lunchbreak...
additional info:
Bench tested FI relay, have voltage at "inner 87" post with no power to relay coil.
With power to relay coil, relay clicks and have power to "outer 87" post.
Seems to me that the FI relay is working correctly.
put FI relay in it's socket, have voltage at 4-wire connector the goes to tank.
press starter button and this voltage rapidly drops to zero.
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Sounds to me that the wrong type of relay is mounted.....switching output,
instead of double output.
When the coil isn't energized it should not be power at the output terminals,
when power is applied to the coil you should have power to both outputs.
A relay with switching output have the terminal designation 87a + 87b.
A relay with double output have the terminal designation 87 + 87.
You should have the later one.
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inge k is always so technical...
im a simple motobricker... so...
with moto on center stand... kickstand up... in neutral... clutch lever pulled in... ignition off...
switch ignition on... hit and release start button...
do you have headlight... do you have horn...
j o
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Inge K.,
I have been pondering that perhaps it was an incorrect relay.
Just bought this bike 3 weeks ago, not running.
When I bought her I was advised that the fuel pump needed replacement.
Am a complete newbie to the K-Bike, and wouldn't know a correct FI relay from an incorrect FI relay by sight.
It would seem that in it's prior life the relay was incorrectly changed.
Will get a correct relay ASAP!!
Thanks so much, will report back.
Johnny, When I put her on the centerstand and hotwire the #6 fuse and every system works. She runs like a dream!
Take the jumper wire out, put the fuse back in and she runs 3-5 seconds and dies.
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... Just bought this bike 3 weeks ago, not running.
When I bought her I was advised that the fuel pump needed replacement....
That should have been the first line of your first post in this thread.
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never woulda guessed it was a bastardized new to you nonrunner... thanks for the intel...
j o
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Sorry, I should have put the info regarding the bike status & background situation early on. New at this.
Nothing on the bike is bastardized, just had been taken off the road for a fuel pump replacement.
I bought it knowing I would have to complete that maintenance.
Good news, have confirmed that it is an incorrect FI relay.
Not sure how that got installed, but, all is well now.
It is a perfectly good relay, just not the right one for the job.
A great lesson in diagnosis!
All in all, am glad that I spent the last 3 weeks going over the entire bike, and reading all of the info here.
Have a much greater understanding of and appreciation for the K-bike than if it had been good-to-go on Day 1.
Thank you all!!!
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Stumbled on this threadl searching for information on the fuel pump since my K100 conked out last night. That's an impressive diagnosis from Inge. But it won't help me. There's a kind of whirring noise when the ignition is turned on that lasts a second or two. What is that, the fuel pump? If I open the filler cap should I be able to hear it running permanently?
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The pump will run for a very short time when the ignition is turned on. It will run when the starter is cranking. And it will run if ignition is on and the flap on the AFM is open. Otherwise, it doesn't run.
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I pulled off the fuel hose from the pump outlet of the tank and pushed the starter. Fuel comes out but only as if it were free flowing. I just read that it should be 65 psi. I'm guessing I've got nowhere near that, does that sound right? Also, should fuel pore out of the tank from the return pipe connection when this hose is taken off? The reason I ask is, I have the original owner's manual which describes how to take of the tank but doesn't mention this. I'm rather amazed that BMW l would explain to how to take the tank off instead of advising the owner to go to the dealer, moreso when taking the hose off lets all the fuel out.
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Took out the pump and filter. The plastic base of the pump seems to be warped. Blew through the filter, I'm going to try without the filter to see if there's visibly any more pressure when I hit the starter.
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I pulled off the fuel hose from the pump outlet of the tank and pushed the starter. Fuel comes out but only as if it were free flowing. I just read that it should be 65 psi. I'm guessing I've got nowhere near that, does that sound right? Also, should fuel pore out of the tank from the return pipe connection when this hose is taken off? The reason I ask is, I have the original owner's manual which describes how to take of the tank but doesn't mention this. I'm rather amazed that BMW l would explain to how to take the tank off instead of advising the owner to go to the dealer, moreso when taking the hose off lets all the fuel out.
http://www.motobrick.com/index.php/topic,6200.msg41283.html#msg41283
I guess since the only time I'd really ever disconnect the fuel lines is to remove the tank and that requires disconnecting the power connector, I think Inge's suggestion in the above thread makes a lot of sense. Or, a large rag. Next time, I'm going to have a plug handy.