Vacuum leak on gas Allegro??

[beany]

Hi Folk....
We have a 2005 Allegro on a workhorse platform and have noticed a hissing sound coming from the rear of the RV. Seems to be a constant vacuum leak or air pressure leak sound but everything works fine and could find no source while snooping around underneath. Its a gas rig so shouldn't be any vacuum lines or air pressure.
Any thoughts on what it might be and should I be worried ???
As Always.. Thanks Guys
Don Ashley

[olfarmer]

Sorry double post.

[olfarmer]

We had to have the in tank fuel pump on our 2001 Winnebago with a Workhorse chassis replaced last summer. The original pump never made any noise. The new GM replacement makes a "whirring" sound if you stand near the back of the MH. I have had Chevy pickups that did the same.

[Rick_Jay]

I believe what you are hearing is the normal sound of the in-tank fuel pump.

How long have you had this motorhome?

~Rick

[wildmanbaker]

Don,

You may have found a problem in the developing. Usually, if an in tank fuel pump starts making noise, it is on a short course to failure, and usually in hotter weather.

Good luck

[wildmanbaker]

Don,

You may have found a problem in the developing. Usually, if an in tank fuel pump starts making noise, it is on a short course to failure, and usually in hotter weather.

Good luck

[beany]

wolfe10 wrote:
Don,

Not aware of any vacuum or pressure line in the back of a gas coach. Do you have supplemental rear air bags???

No , no air bags. It sounded loudest center of fuel tank , at least from under neath. Maybe a intank fuel pump pooping out ???

[Argosy24]

It should show as a fault, a check engine light.

[rgatijnet1]

Argosy24 wrote:

rgatijnet1 wrote:
If it only happens when the engine is running it could be from the fuel cap that is making noise as air is sucked in to replace the fuel being used. A new fuel cap may eliminate the noise.

The caps are sealed now as part of emissions, air to replace fuel used comes through the carbon canister.

That is exactly right, but suppose the seal is not good on the fuel cap. I assume this is something that has not been going on since the coach was new so it may be possible that the seal could have cracked or split on the fuel cap.

[wolfe10]

Don,

Not aware of any vacuum or pressure line in the back of a gas coach. Do you have supplemental rear air bags???

[Argosy24]

rgatijnet1 wrote:
If it only happens when the engine is running it could be from the fuel cap that is making noise as air is sucked in to replace the fuel being used. A new fuel cap may eliminate the noise.

The caps are sealed now as part of emissions, air to replace fuel used comes through the carbon canister.

[path1]

Took me awhile to find out I had nothing more than a cracked vacuum line (rubber hose). See if this makes it any easier if nobody can tell you exactly what it might be. http://www.youtube.com/results?search_query=find+vacuum+leak&sm=12

[rgatijnet1]

If it only happens when the engine is running it could be from the fuel cap that is making noise as air is sucked in to replace the fuel being used. A new fuel cap may eliminate the noise.

[Argosy24]

Fuel pump?