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Discussion Starter · #1 ·
Hey Guys,

Tried to go for a Sunday ride and got as far as the driveway! Fuel pump fuse 15 amp keeps blowing. This is out of nowhere....been riding the bike everyday for a month w/ no issues. Before I get my volt meter and take things apart....any known issues with my 95 900 SP fuel pump fuse blowing.

I the only electrical work I have done this month was replacing rear tailight assembly a week ago.

Thanks
 

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You could try checking the wires coming out of the fuel sending unit. Pull back the boot and see if any of them are frayed. 3 of my 4 wires were and causing my fuel pump to be inop sometimes. If they are touching each other also, it could pop a fuse.

Only other thing I can think of is the fuel pump itself.
 

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in addition to above,,,,remove pump/filter and bench test. just apply 12v and see if motor runs or not.
 

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Fuel Filter Electrical Load

The design basis current rating of the fuel pump is 5 amp. Ducati fuel injection systems use a high pressure fuel pump powered by a DC motor that draws a fairly-high current and a dirty/clogged fuel filter will causes the motor to work harder and draw a much higher current. So the in-line fuel filter inside the gas tank requires regular replacement. A pump feeding fuel through a clean filter will draw about 2 - 5 amps, but this figure can rise to 10 amps or higher with a dirty filter. Try changing the filter.
 

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Discussion Starter · #5 · (Edited)
Thanks guys, I did some non electrical/volt meter testing and found a rather bizarre scenerio~

I did find one of the black wires under the tank for the pump flattened and some insulation gone.(there were two and assuming one of them is the ground) It must have been sandwiched between the frame. I isolated the wire and taped it up temporarily. Here is the weird thing.

The pump is running fine with the tank up and unlatched. As I bring it down everything is still good. I hook the latch to the frame and as soon as I latch it down the fuse blows! I looked for 30 minutes to see what wire/relay can be "catching" or crushing when the tank if latched and couldn't find anything. I even pulled the wiring for the pump away from the frame or anything metal. I did this test while my buddy watched 10 times! I'm glad I have a box of 50 15 AMP fuses. Does the latch on our bikes complete some type of circuit to ground? Are there wires attached to it inside the tank for the latch? I'm just really dumbfounded. I also tried leaving the unlatched and just using my body weight to push the tank down and fuse doesn't blow. SO I'm pretty sure it's not a physical issue causing the problem. :think:

***UPDATE***

I found an interesting fix for now, I put electrical tape on the tank where the metal catch makes contact when "locked" down. No more blowing fuse but I'm afraid this may be a dangerous band aid to the issue. Something inside the tank may be shorting out and when the catch makes contact with the tank body....it completes the circuit and pop! Wish I paid more attention in electrical 101.
 

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Discussion Starter · #6 ·
The design basis current rating of the fuel pump is 5 amp. Ducati fuel injection systems use a high pressure fuel pump powered by a DC motor that draws a fairly-high current and a dirty/clogged fuel filter will causes the motor to work harder and draw a much higher current. So the in-line fuel filter inside the gas tank requires regular replacement. A pump feeding fuel through a clean filter will draw about 2 - 5 amps, but this figure can rise to 10 amps or higher with a dirty filter. Try changing the filter.
My bike is not fuel injected....carbs here.....does your suggestion still apply?
 

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A dirty filter is still bad for the pump. Whether it is enough to blow a fuse or not, I don't know.

Last time I had mine serviced the mechanic gave me "that look" when he mentioned my fuel filter. I did feel better that I had asked him to replace it though.
 

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Thanks guys, I did some non electrical/volt meter testing and found a rather bizarre scenerio~

I did find one of the black wires under the tank for the pump flattened and some insulation gone.(there were two and assuming one of them is the ground) It must have been sandwiched between the frame. I isolated the wire and taped it up temporarily. Here is the weird thing.

The pump is running fine with the tank up and unlatched. As I bring it down everything is still good. I hook the latch to the frame and as soon as I latch it down the fuse blows! I looked for 30 minutes to see what wire/relay can be "catching" or crushing when the tank if latched and couldn't find anything. I even pulled the wiring for the pump away from the frame or anything metal. I did this test while my buddy watched 10 times! I'm glad I have a box of 50 15 AMP fuses. Does the latch on our bikes complete some type of circuit to ground? Are there wires attached to it inside the tank for the latch? I'm just really dumbfounded. I also tried leaving the unlatched and just using my body weight to push the tank down and fuse doesn't blow. SO I'm pretty sure it's not a physical issue causing the problem. :think:
hi there.

have you taken the entire pump assembly out of
the tank already ?
i'd do that to take a look how things are set-up inside,
fuel pump and filter work, most annoying thing on our
lovely bikes.

anyway, you have my best wishes.

cheers. :)
 

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Discussion Starter · #9 · (Edited)
hi there.

have you taken the entire pump assembly out of
the tank already ?
i'd do that to take a look how things are set-up inside,
fuel pump and filter work, most annoying thing on our
lovely bikes.

anyway, you have my best wishes.

cheers. :)
Will take out the assembly after some sleep. Set if is similar to my M5, fuel pump and filter are inside tank fully submerged in fuel! Do you have any hints of what's causing this weird issue?

***UPDATE HERE IS SOME CRAZY SH*t!

I didn't get a chance to pull the pump/filter assembly today due to other pressing matters. But did find this out! My gas tank is electrified with the ignition on!!!!!! I took a test light and was able to get 12 volts from the latch, petcock, back hindge and tip of vent! So I'm thinking there is some bad wiring issues inside the tank just like Muschi suggested. A local forum member wants to help me find a frayed wire by the ignition switch....which he believes is the cause. Just thought I'd share this in case it has happened to someone else before!

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hm no to be honest, but it is rather early in the day still,
i hope for some enlightment later on.

;)
 

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Discussion Starter · #11 · (Edited)
Update

Finally got the fuel pump assembly out. tested pump, it was fine. Replaced filter and checked all wiring....found no faults.

Put everything back together and tank no longer lights up the test light and fuse not blowing! I'm frustrated because I didn't find any obvious faults and even though problem has been resolved.....it's cause is still unknown and will still haunt me when I'm 100+ miles away from home and it happens again. :mad: Thanks for all the advice though....very much appreciated.
 

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That's crazy you were getting power through the tank. It sounds like one of your fuel pump wires is shorting to the tank, thus when you latched it to the frame it completed the short to ground and blew the fuse. Make sure you inspect the insulation on the wires carefully.
 

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Discussion Starter · #13 ·
That's crazy you were getting power through the tank. It sounds like one of your fuel pump wires is shorting to the tank, thus when you latched it to the frame it completed the short to ground and blew the fuse. Make sure you inspect the insulation on the wires carefully.
Thanks for that. I couldn't see any frays or damage to the insulation. I was suprised the wires look like speaker wire at first because on was cooper and the other silver. (insulation is clear plastic) I will check again with a meter after I go thru this tank of fuel. Silly question.....there is no repairing any frays or damage to wiring submerged in gasoline right? If I have to replace the wires, it looks like I would have to replace the low fuel sensor too!
 

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hmmm.. i have seen this type of problem before on cars. Pump motor shorts to pump case, pump case is inadequately isolated from the pump bracket and then 12v is shunted to ground via your gas tank which popped the fuse.

The wierd thing for me was when you had the test light lit earlier.. i guess just maybe at that moment in time the energized tank was isolated from the frame (via the loose hinge and unlatched hook). Who knows but im sure you will see this again. I would imagine regardless of your symptoms the shiny arrow will lead eventually back to the fuel pump itself.

Maybe thats why it ran until you got to the end of the drive way earlier.. was it when you went across a bump that it turned off? The tank was isolated from ground (frame) and the "bump" made contact shunting the voltage to ground and pop.
 

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Discussion Starter · #15 ·
hmmm.. i have seen this type of problem before on cars. Pump motor shorts to pump case, pump case is inadequately isolated from the pump bracket and then 12v is shunted to ground via your gas tank which popped the fuse.

The wierd thing for me was when you had the test light lit earlier.. i guess just maybe at that moment in time the energized tank was isolated from the frame (via the loose hinge and unlatched hook). Who knows but im sure you will see this again. I would imagine regardless of your symptoms the shiny arrow will lead eventually back to the fuel pump itself.

Maybe thats why it ran until you got to the end of the drive way earlier.. was it when you went across a bump that it turned off? The tank was isolated from ground (frame) and the "bump" made contact shunting the voltage to ground and pop.

The techs at the dealership were scratching their heads too on this one. The fuse popped before I hit the "bump" in the driveway. If anything I think part of the reason for this was I let the tank go almost empty this week because I wanted to replace the fuel filter and change the oil. When I first opened the tank I noticed the wires for the pump were resting on the left side of the tank wall. So if there is a break it would have been in that section of wire. Since I always keep my tank full. (I fill up every 60+ miles) the wire was always suspended in the fuel and didn't have a chance to touch the side of the tank. That is my theory.:think: Do you know if the wires is suppose to be just "floating" around in there or should it be anchored to something?

Not sure if this applies but the pump is encased in a rubber boot so not sure how a 12V leak from the pump body can transfer to the tank. Can fuel actually be electrified?
 
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