I need help!!!!! Just took off my smarty jr and now I have a hissing sound coming from the fuel rail. It gets louder the further back the rail you go.

 

I have what sounds like a similar problem, been trying to resolve it for 6 months with no luck. Mine sounds almost like a belt squeel, kind of high pitched hissing ( or like an excavator hydraulic maxing out). I've poked all over with a stethescope and keep coming back to the rail. My first thought was that a little fuel was leaking past the relief valve so i put a plug in the banjo bolt and it still does it. Mine doesn't do it all the time but when it does make noise i seem to be down on power and fuel mileage and i notice my low press fuel drops a few psi like its flowing extra fuel somewhere. I can't think of anything else that could make such a sound from the rail. If you figure it out keep me posted!!

 

Are you both sure it is not a boost leak, coming from one of the connections on the intake horn or boost hose?

When the rail relief valve releases, it is more of a cycling "pop pop pop" when the valve opens and reseats. I suppose the relief valve could be stuck partially open, but you would be way down on power.

 

Where is the rail relief valve located. pics would help. can't tell if I'm down on power since it is back to the stock setting. My next question is why does it go away when I install the jr back on?

 

not sure about the original poster but i pressure tested intake for boost leaks and found nothing. I was thinking the large gasket on the bottom of the intake horn but it seemed fine. Rail relief is the small cylinder that comes vertically off the rail with a return line that goes down to the side of the fuel filter mount. my theory with the relief valve is that if they don't pop all the way maybe they can just leak a little fuel by (making the whistling noise) and then re-seat sometimes. Isn't the valve spring loaded so can those springs wear?

 

It can't be a boost leak at an idle can it??? The noise seems to stop with the jr installed

 

If the jr seems to make yours stop i wonder if that can help me narrow down the cause. I've had every dealer and cummins shop in town listen to mine and no one has any ideas so i had almost given up. Mine is loud at idle then seems to fade or get drowned out with increased rpms so i still think its high pressure fuel sound leaking past something and not boost related. I thought maybe an injector sticking or worn ball seats leaking too much return fuel might make some noise but nobody (including Don M) thinks injector issues make any noise. Or a loose connector tube but i don't see any fuel leaks and oil analysis showed no fuel. Then i was thinking that maybe even with the plugged banjo bolt on top of the rail relief valve that maybe fuel was still leaking past the valve and flowing around the coarse threads of the banjo bolt.

Would the jr change rail pressure at idle? Or if it were injector related i wonder if changing the timing has an affect? sounds like another real good excuse for me to get a jr.....

 

Hopefully Bob or Marco see this and chime in with some answers