Vapor Tank Question

[HusseinHolland]

Interesting read. I didn't think my 75 (CA market) had a vented cap of any sort, but since it is described as such here, I looked at the pic I took when I changed the gasket - it does appear to have a valve in the center. I'll have to look under for the check valve - I didn't see any sign of it when I did the fuel pump work. I will be dropping my tank to take care of the vapor hoses (and probably bypass the vent tank). If there's space, I'd also like to add a later charcoal cannister in the back, to free up the bay for when I do the V6 conversion.

[Captain Obvious]

2 hours ago, Yarb said:

Thanks @Captain ObviousBut that sure made my brain burp as well!!😂😂

Perfect. Then my work here is done.   

[chaseincats]

So in this case it sounds like the check valve wouldn't be a leak point for fuel vapors - bummer

[Zed Head]

On 11/7/2023 at 9:58 AM, Zed Head said:

What did you do with the open end of the hose?

My question was about the big hose.  Where the fumes would be emitted.  Did you block it?  That will pressurize the tank.  Did you leave it open?  That will cause a gas smell as it's open to the tank.  Did you leave it connected but with no purge line to the intake manifold?  That will also cause a gas smell after the canister charcoal gets loaded with gas vapors.

[chaseincats]

2 hours ago, Zed Head said:

My question was about the big hose.  Where the fumes would be emitted.  Did you block it?  That will pressurize the tank.  Did you leave it open?  That will cause a gas smell as it's open to the tank.  Did you leave it connected but with no purge line to the intake manifold?  That will also cause a gas smell after the canister charcoal gets loaded with gas vapors.

That line is open with the inlet port on the intake manifold capped.  I just don't understand how the fuel tank vapors are getting into the cabin since I can't find any leaks in the back...

[Zed Head]

The biggest one.  The one that goes back to the tank.  The one that you tried to blow through.  Is it open now, connected, or blocked?

You said earlier that something was disconnected.  Trying to figure out where the end of the main hose is.  If it's still connected to the canister but the purge hose is disconnected, the canister can get "full".  The charcoal only absorbs a certain amount of vapor.  Fumes in the engine bay can get sucked in through the cowl vent, and leak in through the various holes in the firewall.

[chaseincats]

1 hour ago, Zed Head said:

The biggest one.  The one that goes back to the tank.  The one that you tried to blow through.  Is it open now, connected, or blocked?

You said earlier that something was disconnected.  Trying to figure out where the end of the main hose is.  If it's still connected to the canister but the purge hose is disconnected, the canister can get "full".  The charcoal only absorbs a certain amount of vapor.  Fumes in the engine bay can get sucked in through the cowl vent, and leak in through the various holes in the firewall.

That is currently connected (the line from the tank into the carbon canister inlet port) to the carbon canister.  Originally, when I noticed the fuel vapor smell in the cabin, that line was completely disconnected (but as it sits now, that is the only thing connected to the carbon canister).

[chaseincats]

This hit me today.  Why not plug the metal line in the engine bay that comes from the vapor tank into the t-connector that the carbon canister's vacuum actuator outlet ordinarily would plug into?  The vapors would still be going into the intake manifold, just through a different opening.

Since I can't find the gasoline smell location from the vapor tank area, getting the vapor tank venting system working is the next best thing but since my carbon canister doesn't hold vacuum, that's how I came to this.

Edited March 31, 2024 by chaseincats

[Zed Head]

It's not the canister that holds vacuum it's the cap on the top.  The canister is completely open on the bottom.

It might be that the canister "charcoal/carbon" in the canister is saturated, coated, or clogged.  The basic concpet is that the gasoline vapors enter the pores of the carbonaceous material and stick until they are pulled off by air entering through the bottom.  But the material does not last forever.

https://www.carparts.com/blog/5-signs-youre-due-for-a-charcoal-canister-replacement/

[chaseincats]

1 minute ago, Zed Head said:

It's not the canister that holds vacuum it's the cap on the top.  The canister is completely open on the bottom.

It might be that the canister "charcoal/carbon" in the canister is saturated, coated, or clogged.  The basic concpet is that the gasoline vapors enter the pores of the carbonaceous material and stick until they are pulled off by air entering through the bottom.  But the material does not last forever.

https://www.carparts.com/blog/5-signs-youre-due-for-a-charcoal-canister-replacement/

Sorry, I should have said the top vacuum operated portion no longer holds vacuum.  Would wiring it that way work?

Edited April 1, 2024 by chaseincats

[Yarb]

Go to @Dave WM post and see how he found one I believe off of an older pathfinder that worked. You may find that your issue is back at the tank. There’s a check valve in place back there as well.

[chaseincats]

Just now, Yarb said:

Go to @Dave WM post and see how he found one I believe off of an older pathfinder that worked. You may find that your issue is back at the tank. There’s a check valve in place back there as well.

I shouldn't be able to smell the gas vapors if it is the tank though since it is isolated from the cabin I'd think.  One of my hoses has to have a rip somewhere but I can't find it.

The frustrating part is the only time I can smell it is when I'm driving or if I blow hard in the charcoal canister metal line...

Edited April 1, 2024 by chaseincats