Fuel Vapor Whistle

[70 FJ40]

I've had what sounds like a high pitched elctrical whine in my 40 for a while now. It's very intermittent. Sounds like the seat belt buzzer just much quieter. I looked all over for some electrical doodad that might be causing the noise. Finally was able to pinpoint the sound coming from the fuel vapor separator. I can make the noise stop by tapping on the metal cover or taking the gas cap off. But the noise returns fairly quickly if the weather is hot. Do I need a new vapor separator? Can I get one? Is there a way to fix the one I've got so it doest whistle? Also curios if anyone else has experienced this. Seems kinda unique to me but maybe not.

 

[B y r o n]

Since you can make it go away by cracking the gas cap indicates a blockage somewhere. Can you disconnect the line going to the charcoal canister, located in the engine compartment, when it is making noise. If the noise stops then thee problem is likely the charcoal canister and not the vapor separator.

 

[70 FJ40]

Thanks. I'll give that a try. The noise is definitely coming from the separator. But I suppose the blockage could be somewhere other than the separator, but the separator is what makes the noise?

 

[Pighead]

but the separator is what makes the noise?

Maybe a connection at the separator is the weakest link in your system?
My '74 55 whistles too. From the gascap I'm pretty sure. Usually when the aft-end, where the gastank is, is in the sun. Sometimes after a long drive. It's done that as long as I can remember. My vapor recovery system is pretty much stock and intact, except the charcoal canister vents to atmosphere. I've accepted it as normal, though I don't know just why it happens. If I don't feel a whoosh outward when I remove the gascap I worry. If I feel a whoosh inward it's probably a bad fuel filter again.

 

[numby]

Is there a check valve just after the separator on the line heading toward the tank? When the engine is running the vapors get sucked through it on their way to the charcoal canister. They can kind of buzz if you blow hard enough through them.

 

[Paul_A]

I had a 1970 that after I shut it down you could hear a long wheeze as the pressure in the tank escaped. It probably made that noise when it was warmed up and running but tire noise and rattles drowned it out.

 

[Pighead]

I theorize that the fuelpump likes a little positive pressure from the fueltank, makes it's job easier...

 

[70 FJ40]

I finally got a few minutes to do a little more digging for this whistle. I do not have a charcoal canister. (Didn't think I did.) It was likely removed when the desmog happened by a PO. There is a small white check valve on the line between the separator and where the line exits the cab headed to the engine bay where the charcoal canister would be. In the engine bay, it looks like whoever did the desmog just put a fuel line in place of the charcoal canister.

 

[70 FJ40]

I'm thinking I'll just remove that check valve and see if the whistle stops. If so, I'll buy a new check valve.

 

[70 FJ40]

I removed the check valve and blew through it. Sure enough, it whistles. I guess I will replace the valve. Now, to see if I can buy a new one.

 

[numby]

I removed the check valve and blew through it. Sure enough, it whistles. I guess I will replace the valve. Now, to see if I can buy a new one.

Don't bother. They almost all whistle. You problem is that you've got vacuum from the engine sucking your tank vapors straight through because you don't have the canister and the OVCV (outer vent control valve). That *could* be dangerous in a rollover if the engine is running and gas is getting sucked straight into the cylinders below the throttle valve.

If you're sticking with the CC delete then you'll need to do something. Your tank needs to vent outward. Some have run a loop of hose from the tank vent line up the firewall (engine side) and back down under the car to the rear. Cap it with a fuel filter just to keep dust out. Some people drill straight thru the gas cap to let the tank vent in and out. Best would be getting a CC. Anything else is and possibly unsafe.