Vapor Tank Question

[chaseincats]

1 hour ago, Zed Head said:

 

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

 

Sorry if I'm not explaining this properly.

The purge line is connected where the vacuum actuator line used to connect (the t-fitting by the throttle body) - for the idle vacuum leak reason.  The purge hose is larger than the hose used for the old vacuum actuator line (which isn't in use now and replaced by the purge hose) so I have a larger t-fitting and had to heat the smaller hose ends to fit on the t-fitting.  Does that make sense?  I can make a video if that would help?

[Zed Head]

I understand what you wrote the first time about bypassing the canister.  

If you're smelling gas it means that the carbon/charcoal media in the canister is either saturated with fuel or it is cracked and not absorbing the vapors properly.  You're trying to redesign the system but what you really need is just new canister material and a properly functioning control valve.  You said that your control vlalve doesn't work.  You might be able to fix yours by opening the purge valve in the cap, drill it or remove the return spring, and using a separate vaccum control vlalve on the purge line.

Welcome to the world of old cars and NLA parts.  Your best bet to get rid of the fuel smell is to get the system back to working like it was designed to work.  A salvage yard canister from a newer car and a vacuum control valve would do it, I think.

 

They show a spring inside the cap.  It must be a pull spring, not a push spring.  That's what keeps the purge valve closed when there's no vacuum.  Anyway, notice also that there's a "fixed orifice".  Meaning small, so that air flow is low.  You could probably remove the cap and connect the purge line directly to the orifice with a vacuum control valve in-line. 

Also, activated carbon is the more technical term than charcoal.  Your carbon has probably lost its activation.

[chaseincats]

10 minutes ago, Zed Head said:

I understand what you wrote the first time about bypassing the canister.  

If you're smelling gas it means that the carbon/charcoal media in the canister is either saturated with fuel or it is cracked and not absorbing the vapors properly.  You're trying to redesign the system but what you really need is just new canister material and a properly functioning control valve.  You said that your control vlalve doesn't work.  You might be able to fix yours by opening the purge valve in the cap, drill it or remove the return spring, and using a separate vaccum control vlalve on the purge line.

Welcome to the world of old cars and NLA parts.  Your best bet to get rid of the fuel smell is to get the system back to working like it was designed to work.  A salvage yard canister from a newer car and a vacuum control valve would do it, I think.

 

They show a spring inside the cap.  It must be a pull spring, not a push spring.  That's what keeps the purge valve closed when there's no vacuum.  Anyway, notice also that there's a "fixed orifice".  Meaning small, so that air flow is low.  You could probably remove the cap and connect the purge line directly to the orifice with a vacuum control valve in-line. 

Also, activated carbon is the more technical term than charcoal.  Your carbon has probably lost its activation.

Got it - ok that makes more sense, sorry.  I originally had the hose just open in the engine bay but never smelled any vapors coming from it - only from the rear of the car in the cabin.  Could my check valve between the vapor tank and carbon canister be bad?  I can blow hard into the line in the engine bay and sometimes smell gas inside the cabin even after changing the hoses (but it got considerably more difficult after changing them).

[Patcon]

Or you smell gas from another source, not the canister...

[Zed Head]

I thought the topic was fuel smell in the engine bay.  There are exposed lines in the cabin behind the plastic, vents and filler plus the tank.  That's a whole different problem.

This link is about 240Z's but the 280Z's are very similar.  Pull the plastic and explore.

https://www.zhome.com/Racing/FuelTankVaporLineMod/FuelTankVaporMod.htm

[chaseincats]

10 minutes ago, Patcon said:

Or you smell gas from another source, not the canister...

I smell gas in the rear of the car on the inside - coming from the vapor tank area.  I pressure tested the tank then all hoses and none of them had a leak after I replaced them - but I still will periodically get a fuel smell in the cabin anyway.  Hooking up the carbon canister (the hose was open since I got the car) was my idea to fix the issue because I thought vacuum was pulled through the canister to pull fuel vapors out of the vapor tank but I now know that isn't how it works 😞.

[chaseincats]

1 minute ago, Zed Head said:

I thought the topic was fuel smell in the engine bay.  There are exposed lines in the cabin behind the plastic, vents and filler plus the tank.  That's a whole different problem.

This link is about 240Z's but the 280Z's are very similar.  Pull the plastic and explore.

https://www.zhome.com/Racing/FuelTankVaporLineMod/FuelTankVaporMod.htm

No, it was me thinking that hooking up the carbon canister in the engine would pull fuel vapors out of the vapor tank since replacing the hoses/pressure testing everything back there seemed to show no leaks.

[Zed Head]

The other typical fuel smell source is the exhaust.  It gets pulled through various small gaps in the back.  Ironically, gets worse with the windows down, the pressure differential changes.  The biggest improvement seems to come from sealing the edges of the vinyl covered panel on the hatch lid.  The fumes get sucked in around the latch and the two holes on the corners.  The other biggy is the tailight gaskets.

[chaseincats]

2 hours ago, Zed Head said:

The other typical fuel smell source is the exhaust.  It gets pulled through various small gaps in the back.  Ironically, gets worse with the windows down, the pressure differential changes.  The biggest improvement seems to come from sealing the edges of the vinyl covered panel on the hatch lid.  The fumes get sucked in around the latch and the two holes on the corners.  The other biggy is the tailight gaskets.

This is definitely a gasoline smell rather than exhaust.  I sealed all exhaust inlets using a smoke machine and shop vac.

If you blow in the line in the engine bay that heads to the vapor tank and scamper back there, you can smell fuel coming out of the area inside the hatch near the vapor tank even though I've changed the hoses 

Edited June 15 by chaseincats

[Patcon]

Then the vapor tank is cracked or you have hoses that are leaking. If your vapor tank is metal then you can tighten the hose clamps with no fear...

[chaseincats]

4 minutes ago, Patcon said:

Then the vapor tank is cracked or you have hoses that are leaking. If your vapor tank is metal then you can tighten the hose clamps with no fear...

I took every hose and the vapor tank out and tried to blow in one end while keeping the exits plugged and none of them had a leak which is what's so frustrating about all of this.  Any idea where the check valve is under the car that goes from the tank to the engine bay?

[Yarb]

The check valve for the  tank vent is right in the middle of the cross member near the diff. IIRC.