Too much fuel pressure - Ducati.ms

longdrive · May 29th, 2011, 8:38 am

Made the mistake of over filling my tank on a hot day, filled it almost to the filler neck then rode it for a few miles and parked it in the sun. A couple hours later I tried to fire her up with no luck. The combination of a full tank of gas with no room for expansion, no venting, the sun beating down & the motor acting like a hot plate lead to the fuel line blowing off the fuel pump. So if you have the symptoms of no fuel try this first before you waste an hour taking off the fairings, checking hoses & making her feel bad.
Drain your tank down to quarter full & with the tank cap open turn your key to on and listen, if a line is blown off you'll hear it splashing all over inside the tank, be careful not to get an eye full. When the key is turned on the pump primes and pressurizes the fuel lines with the injectors closed, too much tank pressure causes the fuel lines to be over pressurized. As it turns out, it was a blessing in disguise, when I pulled the fuel pump assembly the hose was blown off the fuel pump outlet but the other hoses were shot, I mean the rubber was crumbling and should have been replaced sooner. The clamps are reusable just need about 8" of 5/16" hose (that's I.D.) a fuel filter & new O ring seal. So lesson learned, like all women, let'em vent!

Happy trails

'01 ST4

Joe-B · May 29th, 2011, 10:01 am

My ST3s and SS both have overflow vents in the tank. Doesn't the ST4?

mals900ss · May 31st, 2011, 2:50 am

I'm with Joe, I suspect this was just unfortunate timing. It is not uncommon for the hose to come off in the tank, there is a breather system which may or may not be working or blocked up on your tank however it seems extremely unlikely your cause and reaction are related.

Nice pick up all the same and decent tip about getting the tank level down to hear it...

Dmitry · May 31st, 2011, 7:17 am

Not familiar with ST set-up but on a 748 I can see the pump when cap is open, can probably spot a blown off hose.
As for overfilling, there are vents on the tank, most likely you would come back to a pool of gas on the ground if tank was overfilled (been there)

I have to say that your explanation simply does not make sense. Pressure inside the tank made the hose come off the pump? Not possible because pump inside the tank is pressurized with tank so the pressure differential is 0.
Pump operates at over 40 psi and probably can generate 80 psi if the regulator is stuck so we know the hoses can take at least 40 before blowing off, it would only take 20 psi of internal pressure to completely warp your tank.

Most plausible explanation is that it popped off the moment you turned the bike on, 10 year old rubber hose with heat applied and a fresh batch of ethanol infused gas working away at it, and it just gave in

ducsbill · May 31st, 2011, 12:34 pm

I'm remembering something related to the ST series and overflow problems. I think the early STx bikes, those prior to 2005, used a different hose setup for the vent and overflow. Inside the tank all the STx bikes were the same but for some reason the early ones merged the two on the bottom and routed both to the charcoal vent canister. If you overfilled the tank the overflow of raw fuel would go to the canister and cause starting problems. Starting with the 2005 bikes it appears they changed things and used one hose for the vent to the canister and a separate one for the raw fuel overflow.
Bill W.

longdrive · Jun 4th, 2011, 10:05 pm

Ok, I blew the hose off again, this is after I replaced the f.f. and eliminated the canister. is the fuel regulator built into the fuel pump assy? I'm beginning to think it's bad.

'01 ST4

yellow blur · Jun 4th, 2011, 10:31 pm

When you installed the hose over the barb did you use any lube or install it dry? Should be dry.

Did you use submersible fuel hose? If not you'll need to redo the job or the line will degrade.

The hose shouldn't blow off even if the filter is completely plugged fully restricting the flow. Make sure the clamps are tight and you're using the correct size hose.

davy.j · Jun 5th, 2011, 1:24 am

Quote:

Originally Posted by longdrive

Made the mistake of over filling my tank on a hot day, filled it almost to the filler neck then rode it for a few miles and parked it in the sun. A couple hours later I tried to fire her up with no luck. The combination of a full tank of gas with no room for expansion, no venting, the sun beating down & the motor acting like a hot plate lead to the fuel line blowing off the fuel pump. So if you have the symptoms of no fuel try this first before you waste an hour taking off the fairings, checking hoses & making her feel bad.
Drain your tank down to quarter full & with the tank cap open turn your key to on and listen, if a line is blown off you'll hear it splashing all over inside the tank, be careful not to get an eye full. When the key is turned on the pump primes and pressurizes the fuel lines with the injectors closed, too much tank pressure causes the fuel lines to be over pressurized. As it turns out, it was a blessing in disguise, when I pulled the fuel pump assembly the hose was blown off the fuel pump outlet but the other hoses were shot, I mean the rubber was crumbling and should have been replaced sooner. The clamps are reusable just need about 8" of 5/16" hose (that's I.D.) a fuel filter & new O ring seal. So lesson learned, like all women, let'em vent!

Happy trails

'01 ST4

Possibly could be a bit of rubber found it's way into the fuel pressure regulator.