'95 M900, testing the fuel sensor...

[Flip]

Ok back to the topic-

So you know the bulb and fuse are good yes?

So the next thing to try is with the ignition on check to see if you have voltage on the blue/black wire on the sensor connector. If there is none you need to check the wiring between the connector and the fuse box for open circuits or poor connections.

[Capo]

[Luddite]

Thanks, Capo. Very interesting.

That's one complicated unit!

[Flip]

Okay, I've just re-read this thread (I replied earlier using my phone and couldn't be bothered to read it all).

So you have 12v at the connector and the light comes on when you short the terminals suggesting the circuit there is good.

I think the photo Capo posted is from a later bike with an electric fuel pump hence the additional wiring and circuit board whereas the early bikes used the float only to make or break the circuit.

So a silly question- If you shake it does it rattle?

I know it seems unlikely but if you have three sensors all used and of the same rough age is it possible they could all be gummed up with years of crappy fuel.

I know Ducati have had quite a lot of stick over the years about dodgy sender units but personally my twenty one year old bike is still on the original but maybe it's an exception as it's also on the original Regulator/Rectifier too.

[Macflurry]

Hi guys and thank you for all the responses.

Originally Posted by mjgt

If you are going to test it in liquid just use water not petrol, it's safer
You are just 30 odd miles from me if you fancy a ride out bring one with you and we can have a look at it together, I have a multimeter and plenty of water, even got coffee.

Thank you for the offer, and I would have happily taken you up on it but my bike currently needs MOT'ing.

Originally Posted by Flip

So you have 12v at the connector and the light comes on when you short the terminals suggesting the circuit there is good.

I think the photo Capo posted is from a later bike with an electric fuel pump hence the additional wiring and circuit board whereas the early bikes used the float only to make or break the circuit.

So a silly question- If you shake it does it rattle?

I know it seems unlikely but if you have three sensors all used and of the same rough age is it possible they could all be gummed up with years of crappy fuel.

Yes, the circuit appears good and appeared to be a simple make or break circuit, which is why I wanted to check how these older ones work as there's no obvious moving parts for a float.

I managed to find the Monsters wiring diagram to check and confirm it was a simple make/break circuit, so I'm happy bike side is good but could check that it's definitely getting the full 12V.

No, it doesn't rattle. There's no sounds of anything moving in there which brings me back to why I posted this, as I don't know what's inside or how it's supposed to work, I needed to check I wasn't causing more damage to any components by trying to clear stuff out or if this is simply how it's supposed to be.

I know mine is for sure knackered, the one on the spare tank is of unknown history so I assume that one is knackered but number three is supposed to be known working... but as it is used I need to know how they're supposed to work to rule it out properly. A jammed float was what I suspected at first but as they don't appear that you can strip them I'm back to needing to know how they work before I can try to fix it properly. If it was something other than a float, and isn't gravity activated as suggested earlier, then I may need a different approach.

I can try leaving one to soak in something to try and clear out some gunk.

Originally Posted by Capo

The float does not have any switches, it uses some form of capacitance/ induction
I tore one to bits and have photos

The older sensor like mine should be just make or break. The newer ones, if they show a fuel level , will need either a resister ladder or variable resistor on the float to give different readings for the levels. The capacitors on the board will most likely act like a rectifier to smooth out the values that are fed out so the fuel gauge doesn't constantly go up and down with every bump in the road.

[Flip]

A couple of years back during one of my ‘refreshes’ where I replaced the fuel pipes, vacuum tap and pump bits I had the fuel sender out to swap the prone to cracking plastic nut for a nice alloy one.

While it was out of the tank I am 99% certain it rattled as the float ball moved inside.

I’ll look back through my photos to see if it looks the same as yours. It might not help at all but it might give a little clue on what to check next.

[Macflurry]

Originally Posted by Flip

A couple of years back during one of my ‘refreshes’ where I replaced the fuel pipes, vacuum tap and pump bits I had the fuel sender out to swap the prone to cracking plastic nut for a nice alloy one.

While it was out of the tank I am 99% certain it rattled as the float ball moved inside.

I’ll look back through my photos to see if it looks the same as yours. It might not help at all but it might give a little clue on what to check next.

Thank you, but if its a pain don't worry about it. I'll find something too soak mine in and see how it goes.

[Tosh]

Sorry to jump in but, if you have a known bad un, and have a spare, why not cut one open and have a look inside ?

[Macflurry]

Originally Posted by Tosh

Sorry to jump in but, if you have a known bad un, and have a spare, why not cut one open and have a look inside ?

Trust me, it has crossed my mind. But with the price of these used being ridiculous I wanted to confirm if they were knackered before hacking them apart. I can see where they are put together using a circlip at the end but it's ddefinitely not designed to come apart gracefully.