1150 Fuel pump issue

[Paul Young]

I’ve had a man issue with my GS not starting and knew that the battery was ready for changing, so ordered a replacement one that’s turned out fine. I’ve also replaced the starter pack n the last few weeks as it was easier than refurbing the ‘lazy’ one I had fitted. That also turned out fine and the bike turns over as expected. However, the fuel pump wasn’t priming. Now have a new Kemso pump fitted but it’s still not priming (or firing up).

Things I’ve tested:
- Fuse 6 is good and the relay, swapped for the horn one, shows the relay’s working fine
- voltage across the fuse shows 12.5v initially, falling back to zero as the relay clicks
- voltage at the connector below the tank shows the same as above across green/brown pins
- continuity checked from the plug beneath the tank to the back of the plate and to the fuel pump connectors shows all good and no short between them, until I connect the pump, then there’s continuity between green/brown wires through the motor
- Fuel pump connected directly to a spare 12v battery spins up perfectly and sounds sweet
- plugged together, suddenly there’s no initial12.5v at the pump when the ignition key is turned and the pump doesn’t prime. Yet, if I check continuity through the connectors, it checks out fine from the back of the socket on the loom side, all the way to the fuel pump connectors in the tank. Without the pump I get the initial 12.5v but with the pump connected, nothing…

Anybody got ideas please as I’m running out of them..? Thanks

 

[Ian J Hartley]

Your problem may not be voltage, but current.

If you have a poor connection across a switch or relay, then the voltage will look fine under no load, but as soon as you put a current load on like the fuel pump then the voltage will drop so low that the fuel pump won’t run.

The power for the fuel pump is on the Green/white wire which also feeds power to the fuel injectors and lambda probe. Additionally there is an unused connector tucked up on the right frame under the seat (tank breather valve) which can be a source of problems if the wire has chaffed and connecting the frame causing a high resistance path to earth.

I’m taking it that your motronic is powering up fine.

 

[hops]

Hall sensor?

 

[Paul Young]

Your problem may not be voltage, but current.

If you have a poor connection across a switch or relay, then the voltage will look fine under no load, but as soon as you put a current load on like the fuel pump then the voltage will drop so low that the fuel pump won’t run.

The power for the fuel pump is on the Green/white wire which also feeds power to the fuel injectors and lambda probe. Additionally there is an unused connector tucked up on the right frame under the seat (tank breather valve) which can be a source of problems if the wire has chaffed and connecting the frame causing a high resistance path to earth.

I’m taking it that your motronic is powering up fine.

Thanks Ian. I’d hoped you might have an idea for me to look for… How do I test if the motronic is powering up? Is there a telltale?
I’ll start looking for chafing (ooer missus ) but wouldn’t that show up under a continuity test if I check the green/white to earth?

Hall sensor?

Thanks, it was one of my first suspects but it’s not that. I have 12.5v where it should be but not when the fuel pumps connected. I also have a HES tester that showed good results.

 

[DrFarkoff]

@Paul Young Connect an indicator bulb between the Pump power source at the plug and Battery Ground this is important as this tests that you have enough power supply to the pump and by using the Battery ground you negate that there is a bad ground! as @Ian J Hartley has mentioned volts is not a sign of amps !

Once you power up does the Bulb light up ? Bright is good! You have full amps needed, Dim?

Then there is a supply fault! Bridge out the pump relay "load circuit " does it go bright then? The relay likely has burnt contacts Swap it out and do the checks again

Now test the Ground of the circuit ... battery positive through the bulb to ground Brown on the plug Bulb should be bright

People say just connect X to Y but this way you analyse individual parts of the circuit for very little extra effort !

 

[Paul Young]

@Paul Young Connect an indicator bulb between the Pump power source at the plug and Battery Ground this is important as this tests that you have enough power supply to the pump and by using the Battery ground you negate that there is a bad ground! as @Ian J Hartley has mentioned volts is not a sign of amps !

Once you power up does the Bulb light up ? Bright is good! You have full amps needed, Dim?

Then there is a supply fault! Bridge out the pump relay "load circuit " does it go bright then? The relay likely has burnt contacts Swap it out and do the checks again

Now test the Ground of the circuit ... battery positive through the bulb to ground Brown on the plug Bulb should be bright

People say just connect X to Y but this way you analyse individual parts of the circuit for very little extra effort !

That fantastic. Thanks for the step-by-step. I should have time later this week to start on it all so I’ll update as soon as I can.

Do you have a simple explanation/diagram of which of the relay pins I need to bridge?

 

[Brian O]

hi paul,

sorry i dont have any answers for you but you are more than welcome to nip over if you want to measure or compare anything

brian

 

[DrFarkoff]

That fantastic. Thanks for the step-by-step. I should have time later this week to start on it all so I’ll update as soon as I can.

Do you have a simple explanation/diagram of which of the relay pins I need to bridge?

If you pull out the relay If I remember correctly you have 2 wide spades and 3 small ones

The heavy ones are the load circuit

Putting your finger on it when you switch on and press the starter should let you feel a click which is your upstream signal ticked off the list too