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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: SteveCrout on July 17, 2021, 09:20:47 PM
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So, my 1987 K75c was parked in March as I went to work out of town. 60,000 kms and it has always run like a top. I came back and went to start it and it would turn over, idle for a moment and quit. I couldn't hear the fuel pump whirring when I pressed the starter. So far I've done the following:
- checked the ground from battery to frame
- checked the connection between the pump assembly and the harness (the 4 pin connector) and they are all solid
- applied 12 volts to the green and yellow wire to the pump and the pump runs fine
- pulled out the relay for the fuel system and checked the power to pin 30 and have power ok
- checked the red lead on the pin 86 and pressed the starter button and get 12 volts ok
- put the red lead on battery and black on pin 85 of socket and get 12 volts when pressing starter
- pulled the main harness plug and checked for corrosion - none
- battery is fully charged
- neutral light and charge light come on when key is turned on
- I don't hear the pump working before, during or after the starter is pressed
I'd be pleased if someone could make me look goofy and point out a simple solution!
I've looked over the various queries on the site but they all seem to have a different combination of issues. I'm stumped!
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Check/replace the fuel filter. The fibers in fuel filters swell if a bike sits for a while.
See if there's power between the green/white wire and brown wire at the fuel tank connector when you press the start button.
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Thanks Frankenduck - there is power between the green and white and brown and the fuel pump runs if I connect the two to 12 volts. the filter should be OK but I'll have a look. The fuel pump not running when I press the starter has me bugged.
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What does fuse 6 look like? Maybe replace them all anyway.
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there is power between the green and white and brown and the fuel pump runs if I connect the two to 12 volts.
How are you determining that 12V are at the upstream side of the four-pin connector when the ignition is On and the starter button is pressed?
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Thanks Frankenduck - there is power between the green and white and brown and the fuel pump runs if I connect the two to 12 volts. the filter should be OK but I'll have a look. The fuel pump not running when I press the starter has me bugged.
There should only be power between green/white and brown wires when the bike is starting or running. And if there is power to those two wires then the fuel pump should be running.
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Thanks Daveson - the fuse in #6 is 7.5 amp and intact
The power to the pump from brown and the green and white was only when I pressed the starter button - as it should be I think.
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"the pump runs when I apply 12 Volts"
Can you explain how you did that.
Sometimes the fuses are no good even though they look good. You want to deoxit the fuses and plugs too.
If you connect a battery to fuel relay pins 85 and 86 you should hear a click and then have continuity between 30 and both 87 pins.
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Fully testing the relay can keep you from replacing a good relay.
https://youtu.be/IpRWcNoLdwQ
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Another quick way to check, with a jumper wire between 30 and the inner 87 pin, you should hear the pump run, even with the ignition off. If your fuel hoses are too short to do this with the tank lifted, remove battery earth first and connect it after the tank is properly installed.
If it doesn't run, the fuel relay is not your problem.
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Fully testing the relay can keep you from replacing a good relay.
https://youtu.be/IpRWcNoLdwQ
A very easy way to test a relay is to put a 9V battery to the 85 and 86 terminals and listen for a click.
(https://static.bhphoto.com/images/images500x500/energizer_e9vb_9v_alkaline_battery_bulk_1547732708_1450633.jpg)
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Thanks everyone for your input so far. Work is getting in the way of fixing my toys and it might be a day or so before I can try the helpful suggestions you all posted.
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OK - so I think it's time for an update. I have performed all of the tests suggested on this site and so far - no joy.
I tried it again this morning hoping the boogey man came by and helped me out - no such luck. The engine turns over, there is power to the 4 pin connector to the fuel pump when I press the starter but no starting up. if there is fuel in the rail and a bit of pressure left it'll start and idle for a a few seconds but no acceleration.
I have tested the relay using the jumper across 30 and 87 - no difference
I have tested the continuity of the fuel pump wires by applying 12v to the brown and green wire and hearing the pump run
I have checked the ground wires mid-from and cleaned them all off and used a bit of dielectric grease to ensure they stay clean
I took off the tank and removed the fuel filter and fuel pump units. I bench tested the pump and filter by connecting them and sitting the pump in a jar of fresh fuel then watched as I applied power (from a distance of course - that's why I'm still here!) and ran the pump and it drew the fuel up quickly, passed it through the filter and out the discharge side with considerable pressure. (Don't know if it was the 36 PSI we're all looking for but it felt strong.
the connections to the pump were clean, the connections to the 4 pin wire outside the tank are clean and not receding when plugged in.
It's starting to sound like something is supposed to happen when the ignition is turned on and the starter pressed but isn't. Is this where the Hall effect unit would /should be kicking in?
Thanks again for all your great suggestions. I'm learning lots about the bike as we go along so I don't mind if they don't solve it. I would like to have it running again soon though! It's embarrassing to have a lot of bikes around and none of them functional at the moment!
Thanks again! Steve
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Work is getting in the way of fixing my toys . . .
"the pump runs when I apply 12 Volts" Can you explain how you did that.
If you connect a battery to fuel relay pins 85 and 86 you should hear a click and then have continuity between 30 and both 87 pins.
A very easy way to test a relay is to put a 9V battery to the 85 and 86 terminals and listen for a click.
I have performed all of the tests suggested on this site and so far - no joy.
I tried it again this morning hoping the boogey man came by and helped me out - no such luck.
It's starting to sound like something is supposed to happen when the ignition is turned on and the starter pressed but isn't. Is this where the Hall effect unit would /should be kicking in?
With the jumper wire between 30 and 87, was the pump running?
One problem that has arisen is that you think you're working on a toy. :laughing4-giggles: The next problem is that questions are being asked that you don't seem to be answering. Additionally, you assert you have power upstream of the four-pin fuel pump connector. How have you determined whether there is power downstream of the connector? Also, The boogey man causes trouble; helping is not in his job description. Finally, you might have performed all the suggested tests but you don't seem to have told us all the results.
To answer your Hall sensor question:
The fuel pump relay is activated during starting and it stays activated until the signal from the Hall sensors drops out, e.g., when the starter is shut down, the engine stalls, or the running engine is intentionally shut down.
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Also I don't think you have tested the green/red wire from the fuel injection relay to fuse 6, and it's connections.
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Well, Mr Laitch - I have to admit it's been a while since anyone has given me shit for not taking their advice seriously enough. My apologies for obviously touching a nerve by suggesting I consider the great engineering achievements of the BMW company - a toy.
Although application of Malsow's Hierarchy of Needs would probably find it difficult to place the Beemer on any of the five levels, it is obviously there somewhere for some of us.
That aside, I did forget to mention I tested the fuse connections earlier but forgot to post, I also tested the relay using a lower voltage battery and I could hear the click.
With the jumper between 30 and 87 there was no activity when the key was on and starter pressed.
So this kind of brings me back to the last post - I think I'll look for a way to test the Hall effect unit and go from there.
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How are you determining that 12V are at the upstream side of the four-pin connector when the ignition is On and the starter button is pressed?
Yes I am getting 12 volts from the loom side of the harness when I press the starter button.
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Also I don't think you have tested the green/red wire from the fuel injection relay to fuse 6, and it's connections.
I tested the connections on fuse 6 and they are good. I detected 12 volts at fuse 6 when I pressed the starter button.
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With a jumper wire from 30 to 87 the pump was running on my brick, even with the ignition off, so there was no input or output from the hall sensor. The jumper wire should make a direct connection from the battery to the pump.
Maybe your not getting enough Amps even though the Volts seem good. Maybe use a test light instead of a multimeter, with the jumper wire and working back, probably from the tank four pin plug.
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With a jumper wire from 30 to 87 the pump was running on my brick, even with the ignition off, so there was no input or output from the hall sensor. The jumper wire should make a direct connection from the battery to the pump.
Maybe your not getting enough Amps even though the Volts seem good. Maybe use a test light instead of a multimeter, with the jumper wire and working back, probably from the tank four pin plug.
So - I thought about all the stuff the system was doing and the one thing it wasn't and traced my connections back to their sources. Sure enough, the ground wire on the loom side was corroded through and would connect once in a while but not enough to run properly. I suppose I didn't notice it before because of the pressure maintained in the system even when the pump is shut off.
So I went to the local Lordco and bought a 4 pin connector used on trailers. As it turns out the colour codes are the same brown, green , white and yellow so the cut and re-connect was easy.
So - it runs like it used to and I'm a happy camper!
Once again - thanks to all of you who offered solutions. It was a good exercise in following the circuit from source to application.
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icon_cheers
Fantastic!
This is where I come when I'm out of ideas and need advice.
Often it's the simplest thing, though. . . they don't let you get away with anything, especially the professor.
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Maybe your not getting enough Amps even though the Volts seem good. Maybe use a test light instead of a multimeter, with the jumper wire and working back, probably from the tank four pin plug.
Good advice to use a test light as one with an incandescent lamp will provide a load to the circuit. In a previous life as a Chevy mechanic I remember finding a number of dodgy connections by checking it with a something that provided a load. The new LED ones won't do it.