Low Fuel Light

I was getting close to home yesterday on a 175 mi ride when the low fuel light came on. The fuel gauge shows four bars which would be about right after that distance (I filled up before I left) so I tend to believe the gauge, I really doubt that it's nearly empty. Anyway, I'm guessing there's a problem inside the tank with the sensor. Are they known to fail? Which piece? Any way to diagnose it without going into the tank?

I had the tank open to replace filter & internal lines about 2 yrs & 10K miles ago. It all looked OK and I haven't had any issues till now. Even had the light come on legitimately a couple times. I really don't want to open the tank up unless I really have to. I'm leaning toward filling it up and making sure the fuel gauge still works and if it does just ignore the light. Hell, this is the first bike I've had with a fuel gauge, let alone a low fuel warning (altho the others had reserves). The times it came on I already knew I was pushing it. I'm pretty sure I can live without it, at least until the next fuel filter change.

Anyway, I'm planning to take the tupperware off to add some lighting (Skene Photon Blasters) so I'll check the tank wiring and then decide how to proceed. If isn't one thing, it's another...

Morning Mark

First thing that you need to do is to determine WHAT is off-- the low fuel light or the fuel gauge (it's usually the fuel gauge but that isn't cast in stone)

If it really is the low fuel light that is off then it is working, just not at the correct level.

Those low fuel light in-tank sensors have a couple of issues-

One is-- the float arm gets bent during tank service or fuel pump plate reinstallation. (they usually still work but at the incorrect level)

The other is the float itself starts to deteriorate & chunks fall off.

I have also seen the float hang up on the wires in the tank but in that case they usually just don't work so don't put the light on.

Added: one thing to check is that the tank vent/Evap system isn't plugged. A plugged tank vent or plugged up Evap system can cause the sides of the fuel tank to suck in as the fuel is used out of it. That tank sucking in can crush the fuel gauge float tube & does (temporarily alter the fuel tank shape) -- Do you hear a whooshing sound when opening the fuel filler cap after along ride?

I once worked on a bike (that had lots of chipped inner tank paint) that had the pot contact blade bent that it would not touch the scale. Adjusted/bent it back and it worked just fine.

Dan.

I once worked on a bike (that had lots of chipped inner tank paint) that had the pot contact blade bent that it would not touch the scale. Adjusted/bent it back and it worked just fine.

 

Morning Dan

The 1150RT has a plastic fuel tank so isn't painted inside.

Thanks for the inputs.

To follow up on this...

I had ridden about 175 miles, starting with a full tank, when the low fuel light came on. The fuel gauge still showed four bars which is about what I would expect at that distance.

The tank vents are fine & no apparent distortion of the tank.

Today, I added two gallons of gas to the tank and the gauge went to seven bars. Low fuel light still on.

I put in two more gallons which filled it to the restrictor which is where I started the trip. So I figure four gallons for 175 miles is about 43 MPG which is pretty typical of the mileage I get. The gauge now shows full (which it is) but the low fuel light is still on.

So, my conclusion is that the low fuel sensor is hosed somehow but the gauge is still OK.

My fix...remove the low fuel indicator bulb. I'll keep an eye on the gas gauge and the mileage since fill-up. Next time I have to open the tank I'll deal with repairing it.

And keep my cell phone charged...just in case.

Morning Mark

It sort of sounds like you have a disintegrated float on the low fuel light sensor arm.

When the float falls apart & falls off the wire arm the arm then slowly migrates to the lowest point that it can go & puts on the low fuel light.

Last I knew that float isn't available from BMW so you either have to be resourceful & make one or replace the entire pump pass through assembly. (or just live without the low fuel light)

Yes, you have two independent fuel level senders. The tube that controls the gauge, and the float arm that controls the low fuel light. The low level light usually lights at one or two bars. You can easily be without the light and fix the float next time you are in the tank, or never fix it.