Vapor Tank Question

[HusseinHolland]

On 5/24/2024 at 9:39 PM, Zed Head said:

p.s. I'm not sure I was following what you were reporting in your previous post about liquid in the line.  I thought it was with the #3 tank in place.

 

On 5/24/2024 at 9:50 PM, Captain Obvious said:

So you were getting liquid in the vent line with a stock configuration vent tank and hoses?

Been trying to recall exactly - now I'm thinking the fuel in the vent line at the charcoal canister was AFTER bypassing the vent tank, but before playing around with the charcoal canisters (when I saw the fuel) - this pic is from Monday, the day before. There was an elevated loop in the line, however it was isolated from the 5/8 filler neck / fuel tank vent. SO, I think it is fair to surmise that if the vent tank had been in place, there would NOT have been liquid in the line. 

 

Now I have the two circuits combined again (previous post), I'll know during the week if it is resolved.

Edited May 27 by HusseinHolland

[Captain Obvious]

6 hours ago, HusseinHolland said:

Now I have the two circuits combined again, I'll know during the week if it is resolved.

That looks reasonable. Hope that's the end of the issue!

[chaseincats]

So I ended up hooking my carbon canister back up but noticed the amount of vacuum going into the canister from the engine is not the same level of vacuum going from the canister to the tank.  I pulled the vacuum line off that goes into the canister and pressed the throttle body accelerator arm and put my ear to that hose and it was considerably louder than when I put my ear to the hose that comes out of the canister (the one that heads to the vapor tank). Is my canister plugged or is that how this is supposed to work to not pull full vacuum to the vapor tank?

[HusseinHolland]

There is no (no aspect of the system is designed to pull a vacuum on the tank) vacuum pull on the vapor line from the gas tank/vapor tank circuit. Vacuum only operates on the cannister. The large vacuum line on the purge valve from the intake is the draw, the small vacuum line from the TB is the "switch" that opens the port to allow the large line to pull fuel vapor from the cannister off idle.

Edited June 14 by HusseinHolland

[chaseincats]

9 hours ago, HusseinHolland said:

There is no (no aspect of the system is designed to pull a vacuum on the tank) vacuum pull on the vapor line from the gas tank/vapor tank circuit. Vacuum only operates on the cannister. The large vacuum line on the purge valve from the intake is the draw, the small vacuum line from the TB is the "switch" that opens the port to allow the large line to pull fuel vapor from the cannister off idle.

Right, but I’m not hearing any thing being pulled from the tank-side hose of the canister when off idle when I put the hose up to my ear

[Zed Head]

Vapors are pushed in to the charcoal canister from the tank.  Like when you fill it with cold fuel and the fuel warms up in the sun.  The vacuum hose from the intake manifold pulls air through the charcoal canister, pulling the fuel vapors from the charcoal as the air passes by.  The bottom of the canister is open, so there's no way for the intake system vacuum to pull on the hose back to the tank.

The Nissan engineers created a pretty good pictorial description, although they shouldnt have said "at rest" since they show the vapors flowing to the manifold.  That only happens when running.

[Captain Obvious]

1 hour ago, chaseincats said:

I’m not hearing any thing being pulled from the tank-side hose of the canister when off idle when I put the hose up to my ear

That's normal. The hose that leads to the gas tank is not directly connected to any vacuum source.

Maybe try picturing it this way... The carbon canister is like a big open top bowl full of small rocks. No lid. And there are two tubes stuck deep into the bowl of rocks. One of those tubes goes to the intake manifold and the other tube goes to the gas tank. You can't ever pull a vacuum on the bowl because it's open on the top. There is no lid.

There is a third tube involved, but that third tube doesn't go into the bowl at all. It just actuates a valve switch on the tube leading to the intake manifold.

Not sure I'm helping or hurting at this point.   

[chaseincats]

Gotcha, that makes sense.

I ended up hooking the carbon canister back up assuming (wrongly it seems) that the vacuum would suck the fuel vapors out of the tank instead of having them continue to leak into the cabin (despite changing the hoses).  What I ended up doing was pulling the cap off the vacuum valve and plugging the large purge hose directly into the top nipple (since the valve doesn't hold vacuum), and connecting the purge hose to the T-connector allowing vapors to be sucked in through the throttlebody inlet.  I don't understand why it wasn't done that way to begin with since it's still going into the intake manifold through the throttlebody as you press the pedal...

That said, it sounds like the canister doesn't really pull vacuum from the vapor tank so that idea won't fix the issue.

It's odd because I only smell fuel in the cabin sporadically - I'd have thought if there was a hose leak, I'd smell it all the time.  Have you encountered this?

[Captain Obvious]

6 hours ago, chaseincats said:

it sounds like the canister doesn't really pull vacuum from the vapor tank so that idea won't fix the issue.

Nope. Think about it like "the gas tank will spill over into" the vapor canister.  It's not pulled to the tank. It runs over into.

Thankfully, I don't smell gas fumes with my car ever. I've never messed with the vent hoses in the back by the tank, but I have no idea what (if anything) my previous owner did.

[chaseincats]

23 minutes ago, Captain Obvious said:

Nope. Think about it like "the gas tank will spill over into" the vapor canister.  It's not pulled to the tank. It runs over into.

Thankfully, I don't smell gas fumes with my car ever. I've never messed with the vent hoses in the back by the tank, but I have no idea what (if anything) my previous owner did.

This might be a stupid idea but I’m going to ask it anyway haha.

Could I connect the ported vacuum line on the throttle body to the vapor tank hard line to have the fumes sucked out as I drive?

[Zed Head]

11 hours ago, chaseincats said:

I don't understand why it wasn't done that way to begin with since it's still going into the intake manifold through the throttlebody as you press the pedal...

 

4 hours ago, chaseincats said:

Could I connect the ported vacuum line on the throttle body to the vapor tank hard line to have the fumes sucked out as I drive?

Having the purge hose connected all the time creates a vacuum leak at idle where it will have more impact.  The system is designed to give precise mixtture control at idle speed.  

If you connect directly to the tank you'll have a vacuum leak through the gas cap.  It's vented so that the tank is never under vacuum.  It would be an odd vacuum leak though since it will be pulling gas fumes in with the ait.  Hard to say if it would cause a rich mixture or a lean mixture.

This is page 7 and I don't know if you still have the original charcoal canister or a new one.  The material in the canister does get clogged over time and can also solidify and crack I would guess, leaving open passages back to the tank instead of filtering/capturing the fumes.  Might be that you just need a new(er) canister.  They all work the same so you could just grab a complete canister with control valve on top from a newer car.  That's what I would do.  I looked around for a  new TB controlled system on Rockauto but didn't find one.  But there's probably one out there somewhere.

 

You could also get a new canister for a solenoid controlled system then use a vacuum control valve to control the flow. 

Edited for a better option.  Ports clearly ID'ed.  Tank, purge, air.

https://www.rockauto.com/en/catalog/chevrolet,2002,corvette,5.7l+v8,1380024,exhaust+&+emission,vapor+canister,5180

https://www.rockauto.com/en/moreinfo.php?pk=940007&cc=1380024&pt=5180&jsn=10999

https://www.rockauto.com/en/moreinfo.php?pk=814069&cc=1120903&pt=4980&jsn=1979&optionchoice=0-0-1-1

 

Edited June 15 by Zed Head

[Zed Head]

Here's another that you might actually find in a wrecking yard.  2005 Chevy Impala.  Actually any Chevy around that year might have one.  The hardest part might be finding out where they put it on the car.

https://www.rockauto.com/en/catalog/chevrolet,2005,impala,3.8l+v6,1431102,exhaust+&+emission,vapor+canister,5180