Fuel level sensor - How do they work?

[Riceburner]

On my Rockster I renewed the fuel filter last week as part of a service and since then, the fuel-reserve light has been playing up.

Initially it was stuck "on" (ie lit). Even a full tank of fuel didn't change that.

But I've now done about 100 miles (commute to the office and back) and during those two rides, (I topped up that morning), the reserve light has gone off, then back on again at random intervals (about 10 times per trip).

Initally I thought it might be something to do with leaning the bike and changing something in the tank... but I couldn't replicate that.


So - the main question is... How is the fuel level actually sensed? How does the sensor work? I"m pretty sure it's not a lever with a floating ball on the end, so how is the level actually ascertained?

I'm aware that the GS probably has a different sensor given that you guys get a graded display for fuel level (IIRC) - but I'm guessing that the actual concept of operation will be somewhat similar at least.

 

[Ian J Hartley]

When you took off the pump plate to change the filter, you should have seen something like this.

I believe it to be a float with a magnet which when the level is low enough, the magnet in the float operates a reed switch which the indicates low fuel level.

Clearly the float is operating the reed switch, so electrically it appears sound, but it could be the float is stuck in the tube, or the tube isn’t sitting vertically if the pump plate was misaligned.

Did you orientate the pump plate correctly after the filter change.

 

[Riceburner]

Does anyone happen to have a photo of the underside of the tank showing the orientation of the plate in-situ?
I've a nasty feeling mine might not be pointing "up" correctly.....

 

[Ian J Hartley]

You can’t help marking stuff before disassembly.

Not all tanks in the 1150 range are the same, but all the pump plates are similar. You just have to work it out, but the cut out portion of the pump plate will be facing forward and at about 10 o’clock ish.

 

[Riceburner]

You can’t help marking stuff before disassembly.

Not all tanks in the 1150 range are the same, but all the pump plates are similar. You just have to work it out, but the cut out portion of the pump plate will be facing forward and at about 10 o’clock ish.View attachment 281533

I've never noticed the cutout.......
Cheers for that - you haven't got the same photo, but showing the rest of the tank? (just to make it really obvious!)

 

[Ian J Hartley]

I've never noticed the cutout.......
Cheers for that - you haven't got the same photo, but showing the rest of the tank? (just to make it really obvious!)

No, but you should be able to work it out. With the tank set level, the white float should be positioned vertically.

You will have to take the pump plate off to confirm, but looking at the pump plate should give you some idea whether you have it wrong. Besides, it would be a good idea anyway to check the inside, just in case you have either damaged the float or moved it during your maintenance.

 

[Riceburner]

Well....

This is how it "was" before I removed the plate

You can see the 'flat' and it's up at the top left of the plate.

I removed the plate, and as far as I could make out (without pulling the entire thing out, which is always a pain), it's oriented absolutely fine.

In this view you can see the bottom of the fuel level sensor canister, and the 3 scratches in the underside of the tank are directly underneath the cap, so they represent the "up" direction.

As far as I can make out - it's aligned correctly.

When I put the tank back on, I powered up the bike and the reserve light came on (as you'd expect with a completely empty tank).
I filled it with the 15 litres or so I'd syphoned out, fired it up (to check everything was good), and within a few moments the reserve light went out.

So - maybe it just needed a wiggle? Just needed to be acknowledged, like a small, quiet, otherwise well-behaved child?

I won't know until I ride it for 200+ miles in one go, with a bottle of petrol in the pannier......

In the meantime I'll just rely on the tacho.

 

[Ian J Hartley]

I’m not so sure. Looking at your picture, I don’t think the fuel pump collector is sitting at the lowest point of your tank.

You will know if a your range is down, and if the float still gives you erroneous readings. If it does try moving the pump around one position as indicated.

 

[albatross]

Flat side towards the front U shaped bracket , that’s the correct position on the GS
that determines the position of the float and assures the float arm is free to move.
I think,different floats and arms for GS and GSA with the larger 32 l tank.
But as this has a float switch…..
might be if it’s similar to position of the GS,…as Ian said and he is always right, it needs rotating by one thread set anti-clockwise
Test and try….

 

[Riceburner]

I actually tried rotating it 1/6th of a turn and it wouldn't go. (tried a few times, but no joy at all)

The gubbins internally simply didn't want to rotate any more than about 5 degrees.

It felt like the pump couldn't fit into the narrower part of the tank "under" the plate hole.

I think the fuel pump itself may be oriented differently on the GS/GSA fuel plate than it is on the R-R (The Rockster tank is the same as the R1150R tank).

I can live with it for now: Off to France tomorrow and one of the studs was beginning to feel like a thread was going so I'm not going to mess with it until I get back, or until I stop riding for winter.

 

[albatross]

RB, I am sure if you can’t rotate and there is only said position possible, it will be fine.couldn’t find any repair advice which would show the rockster/R fuel flat position.