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Discussion Starter · #1 ·
Riding 2001 750s when it starts!
Not sure where to post the problem details so here it is
Have been through loads of threads re starting problems but none seem to cover my problem.
Fuel pump is not priming when ignition is switched on.
Relays are good and bike will crank even though fuel system has not primed?
Removed fuel pump and it runs fine connected directly to battery.
Traced wiring and have battery voltage through brown/white wire 4 pin connector under tank and if I connect the pump here to brown/white and black wires pump runs for 5 seconds and then stops as it should.
I still have battery voltage up at red wire at pump connection in the tank after passing through the low fuel level sensor but only if the pump is not connected! As soon as I push the 2 pin connector in on the pump the voltage drops to 0 and the pump obviously wont run. If I connect a bulb in line instead of the pump that wont light either.
If I connect a wire across the 2 connector pins instead of the pump I can get the battery voltage right through to battery negative at ECU pin.
If I check the 2 wires through the low fuel level sensor continuity is good for both and there is no short between them.
Am I missing something obvious or do I just need to get a new low fuel sensor on the assumption that thats the only thing stopping the pump from priming correctly. Can anyone explain to me how this occurs? Electrics is not my strongest discipline as you may have guessed. :confused::confused:
 

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2001 900SSie
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Your electrical skills are fine.
You have done what most of us would do and it is strange.
Given that the pump runs when connected to the main loom connector under the tank, you are right in concluding the problem is in the wiring that is in the fuel level sensor and connector(s) assembly.

The red and black wires for the pump simply pass through the base of the sensor.
The only thing I can suggest is that you measure resistance in the red wire from the outside connector to the pump connector in the tank.

Even there is high resistance, when not connected to the pump, you will still measure close to battery voltage.

Where do you live]?

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I had a similar problem with my 999.
I don't know how similar the pump arrangement is on the two bikes but the 999 has an assembly that is mounted on a cast alloy flange that is sealed into the tank by means of an o-ring. The wiring passes through a resin cast block in the flange so that is sealed. It seems that on a 999 at least, the wiring often breaks inside the insulating sleeve where it passes through the resin, giving intermittent symptoms.
To save myself lots of grief, I simply bought a s/h complete assembly and it solved the problem.
 

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The wires passing through the sensor are prone to breaking and shorting. I had the sensor power wire short and blow a fuse. Other issues can occur due to repeated raising / lowering of the tank. Try checking the electrics with the tank up and down to see if there is a difference.
 

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As soon as I push the 2 pin connector in on the pump the voltage drops to 0 and the pump obviously wont run. If I connect a bulb in line instead of the pump that wont light either.

If I check the 2 wires through the low fuel level sensor continuity is good for both and there is no short between them.
Am I missing something obvious
Possibly the pin in the connector is not locked in? When you push the connector in, it could push the pin or the receptacle terminal out of the connector leaving no connection.

I've seen this happen plenty on the heavy equipment I work on. Some of it uses the exact same connectors used on our bikes. Sounds crazy, I know but big equipment has tiny circuits in places.......sean
 
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I had the same issue. Someone at the factory put the zip ties too close the connectors and pulled them too tight, so the wires are slightly pulled out of the connectors and not making contact. Go all over the bike pushing all the wires back into the connectors from each side. I cut off all of the zip ties near connectors and redid them in a way that won’t pull the wires.
 

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Discussion Starter · #8 ·
Your electrical skills are fine.
You have done what most of us would do and it is strange.
Given that the pump runs when connected to the main loom connector under the tank, you are right in concluding the problem is in the wiring that is in the fuel level sensor and connector(s) assembly.

The red and black wires for the pump simply pass through the base of the sensor.
The only thing I can suggest is that you measure resistance in the red wire from the outside connector to the pump connector in the tank.

Even there is high resistance, when not connected to the pump, you will still measure close to battery voltage.

Where do you live]?

You can edit your details via User CP and then select additional information from memory.
Very similar item.
Update- Resistance was high. After checking prices I decided I had nothing to lose so cut open and dug away at encapsulation (which was surprisingly soft) to reveal a brass ferrule on the inside of the base. Red wire solder joint was not attached and the wire pulled free with no resistance. Trimmed and resoldered wire to ferrule and all working again. Will fill holes with some epoxy putty before refitting just to make sure nothing can vibrate loose later.
If you are going to try this yourself watch out for the components on the circuit board which is in there. Mine had brightly coloured casings so were easy to spot but if you puncture one of these low fuel level sensor will no longer work.
Thanks to all for ideas.
 
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