OK so I'll start with a brief history of the problem. I bought an older ST3 back in November and the first chance I had to ride it was this Saturday.It was low on fuel when I bought it, the fuel guage worked and indicated a level, a bit Ducati guess but it worked. I filled it up with fuel and when I left the fuel station the low fuel light and engine management lights came on and the guage showed zero fuel.The bike ran fine so went for my ride. Just had a chance to look into the problem and it seems there is an electrical connector, inside the tank, which is now below the fuel level and obviously will be shorting out. ( See pictures ).The lead appears to connect to the fuel filler cap at one end and I presume the fuel level sensor at the other end. But this cant be right ( can it ! ). Any knowledge or help much appreciated. Steve R
Thanks Chris, it worries me it might spark while I'm riding it and cause the tank to explode between my legs......... not a good result.
Steve, When i did my pump that puzzled me so i went to the UNI of Google and found that Petrol is not a conductor
That's very interesting. Are you saying that immersed in petrol will not cause a short circuit and that the wire and connector are supposed to be there ? The fact it is ( at the moment ) fully submerged didn't concern me as it has no Oxygen but I was worried as it cleared the fuel level that once it was in free air a spark as it dried out might cause an ignition. Chris thanks for the exploded ( ironically) diagram it looks like it may be a cable from the fuel level sensor which is connected to the fuel filler ? I downloaded an ST3 manual yesterday so will investigate this a bit more later today if I get the time.
Further to the above, have a look at this page from the manual, the leads shown as (A) have a black and white coding and the cables on my connector are black and white so I guess what I am looking at is the connection from the fuel pump to the fuel sensor. Probably says then that the issue is a failed level sensor, which if I'm honest could be a relief as I was worried what else a previous owner may have bodged P.S. the downloaded workshop manual is great.
I've got the exact same fuel system and there several electrical connections submerged in petrol , not least the level sensor which is shown as 11 and 12 on the diagram from Chris Inside of that tube is a strip of circuit board with a double run of wire on it . A float slides up and down and makes an electrical connection between the two wires so that the resistance changes with changing fuel level . It's a pretty crude arrangement and the contacts on the slider are flimsy . Mine was playing up so I pulled it apart and gave it a refresh , which sorted the problem .
Thanks for the reply. The bike had been standing unused for about 4 years before I bought so it is quite likely the contacts are corroded or just dirty from lack of operation then. Very helpful info from you all Thanks. I let you know when I get it sorted.
Getting that sensor tube out is tricky , not least because you'll be working blind . It's held in place by two Terry clips , top and bottom and they are tight . Find the clips by touch , then you need to get a couple of fingers behind the tube and use your thumb to ease each side of the clip away from the tube . You can do a rough test using a multi-meter while tilting / tapping the tube to shift the float . The actual resistance values aren't as important as checking for discontinuity . If the meter goes off-scale it means the contact is lost at the point where the float is .... if that makes sense ?
yes Steve, the non-conducting bit and I agree it's a crazy thing, virtually every manufacturer has decided that there is ZERO chances that a chance spark from a commutator or brush face will ignite fuel because of excluded oxygen but this doesn't explain why there aren't more explosions when in-tank pump motors are energised while tank is empty. For me, this is another reason to make sure you have a "healthy" fuel pump.
The older multi stradas had exactly the same problem with the level sensor. They upgraded it to a better design, not sure if there’s an upgraded one available for the st3. Found this out while searching for potential fuel sensors for my 998.
Thanks Oldtech, are you saying you can remove the sensor without emptying and removing the fuel tank, pump etc? Looks like it's impossible. Any idea what a new sensor might cost ( if you can find one ). Using a mulitmeter is second nature to me is OK I used one half my working life looking for open circuit faults ( Alarm engineer )
Thanks Chris, I never would have guessed, the good news is the fuel pump is brand new,I should have got Moto Rapido to replace the sensor at the same time Doh !
Thanks Bettes, did you find the alternative sensor for the old multi and do you have a link to where you bought it ?
Hi Steve. No, sorry. It’s on the list of things to do sometime in the future. I just came across it while googling it, maybe on here or one of the American forums...
The fuel sensor is held in place by 2 rubber bungs, on on each end of it, and it is simply wedged between the top and bottom of the tank. It can only withdrawn by reaching in through the aperture in the bottom of the tank once you have removed the pump flange. Obviously this will require draining the tank although the tank could be left in place just hinged up. The easiest way to drain the tank it to use the fuel pump. Undo the return line from the base of the tank and put the end of it into a suitable container. There are 2 relays under the seat one of which is for the fuel pump. Pull them out one at a time. When the fuel pump doesn't run at switch on, that's the one you need. With the relay removed and the ignition off use a piece of wire to bridge between the terminal with the brown/white wire and one of the ones with a brown wire. When you switch on the ignition the pump will run without switching off enabling you to pumpall the fuel out.
