Home » Public Forums » GMCnet » [GMCnet] smog/vent?
| [GMCnet] smog/vent? [message #74360] |
Fri, 19 February 2010 13:41  |
Terry Skinner
Messages: 379
Registered: January 2004
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Does any one know anything about the smog/vent thing in the left rear
wheel well?? I have both gas tanks down on this 23 that I am trying to
get home with and the problem with the front tank was the sock on the
end of the fuel pick-up was clogged. The rear tank was the hose was
pinched between the tank and the floor. As suggested by Steve F. I
removed both socks and installed two filters, one for each tank. Now I
am trying to get straightened out the tangle of hoses. Any help would
be appreciated.........Terry
--
Terry Skinner
253-686-2624
Roy. Washington
'76 GMC
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| Re: [GMCnet] smog/vent? [message #74364 is a reply to message #74360] |
Fri, 19 February 2010 14:26  |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
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That thing in the driver's side real wheel well is the fuel/vapor separator. I theoretically (mine passes fuel) prevents fuel from proceeding to the charcoal cannister that is located just inside of the passenger side wheel well in the front. It is a smog thing but really all that is needed is the venting action.
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
visit my gmc blog
click here to visit gmcws.org
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| Re: [GMCnet] smog/vent? [message #74380 is a reply to message #74369] |
Fri, 19 February 2010 18:04 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Gene,
We both looked at that photo and it doesn't show the additional
fitting Terry has on his rear tank.
On Fri, Feb 19, 2010 at 2:13 PM, Mr.erf ERFisher <mr.erfisher@gmail.com> wrote:
> here is one picture of a version (not yours)
>
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=8963
>
> gene
>
>
>
> On Fri, Feb 19, 2010 at 11:41 AM, Terry Skinner <gmcnut@gmail.com> wrote:
>
>> Does any one know anything about the smog/vent thing in the left rear
>> wheel well?? I have both gas tanks down on this 23 that I am trying to
>> get home with and the problem with the front tank was the sock on the
>> end of the fuel pick-up was clogged. The rear tank was the hose was
>> pinched between the tank and the floor. As suggested by Steve F. I
>> removed both socks and installed two filters, one for each tank. Now I
>> am trying to get straightened out the tangle of hoses. Any help would
>> be appreciated.........Terry
>>
>> --
>> Terry Skinner
>> 253-686-2624
>> Roy. Washington
>> '76 GMC
>> _______________________________________________
>> GMCnet mailing list
>> List Information and Subscription Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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>
>
>
> --
> Gene Fisher -- 74-23,77PB/ore/ca
> “Give a man a fish; you have fed him for today --- give him a URL and
> -------
> http://gmcmotorhome.info/
> Alternator Protection Cable
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Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: [GMCnet] smog/vent? [message #74408 is a reply to message #74360] |
Fri, 19 February 2010 21:23 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Terry,
I'm NOT looking at any documentation but here is what I remember. Mounted on the top of each tank is a vent fitting. It is all by it's self and not part of the pick up assembly that you removed to get to the socks. The two fittings (one from each tank) are hooked by a hose to a TEE just sitting somewhere on top of the tanks. It is probably on top of the rear tank. From that "tee" another hose runs to a the fuel separater mounted in the left wheel well. A second hose from the fuel separater runs along the frame rail to the front charcoal canister. If you have a California coach like mine there will be two fuel canisters plumbed in series.
One note on that separater. It is a floating ball check valve that is suppose to shut off if liquid gasoline enters to prevent liquid from entering the line to the charcoal canister. So connecting the correct line to the each port of the separator is important there.
I hope this is the info that you wanted.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] smog/vent? [message #74423 is a reply to message #74408] |
Fri, 19 February 2010 22:51 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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| Ken Burton wrote on Fri, 19 February 2010 21:23 |
Terry,
I'm NOT looking at any documentation but here is what I remember. Mounted on the top of each tank is a vent fitting. It is all by it's self and not part of the pick up assembly that you removed to get to the socks. The two fittings (one from each tank) are hooked by a hose to a TEE just sitting somewhere on top of the tanks. It is probably on top of the rear tank. From that "tee" another hose runs to a the fuel separator mounted in the left wheel well. A second hose from the fuel separator runs along the frame rail to the front charcoal canister. If you have a California coach like mine there will be two fuel canisters plumbed in series.
One note on that separator. It is a floating ball check valve that is suppose to shut off if liquid gasoline enters to prevent liquid from entering the line to the charcoal canister. So connecting the correct line to the each port of the separator is important there.
I hope this is the info that you wanted.
Ken B.
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For a diagram of the vent system see the maint manual X-7425 section 8 page 8-2 figure 1 It shows the layout of the lines. On my 74 GMC did not put the "T" on top of the tanks. It was in the wheel well close to the shield that protects the lines where they cross over the frame and go into the wheel well. If you look just to the left of the left shock absorber on this picture you can see the "T" just above that shield:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=24754&title=getting-started&cat=4936
The hose connections to the separator are shown here:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=30403&title=starting-to-put-it-back-together&cat=4936
As shown in the maint manual the line to the front mounted vapor canister goes to the top connection of the separator.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] smog/vent? [message #74485 is a reply to message #74360] |
Sat, 20 February 2010 15:06 |
Wander Inn
Messages: 100
Registered: January 2010
Location: Phoenix Az.
Karma: 0
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Put a fuel filter between the charcol filter and the engine,
this will stop charcol from getting into the carb.
Mike & Chris Hughes
1977 Kingsley
Phoenix, Az.
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| Re: [GMCnet] smog/vent? [message #74500 is a reply to message #74369] |
Sat, 20 February 2010 19:42 |
Terry Skinner
Messages: 379
Registered: January 2004
Karma: 0
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This is a quote from Gene Fisher's info from Rick.
1. There are two vent systems from each tank. The one we are most concerned
with I call the "Fill Vent" system. It consists of a fairly large (3/8"
IIRC) hose exiting from the top center of each tank, from the pickup/gauge
unit, right next to the fuel outlet hose going to the engine. This hose MUST
be routed high and steady, with no significant dips, to the steel vent pipe
which runs along the side of the coach next to the filler pipe. (A P.O. has
replaced my tee fitting where the front tank fill vent joins the fore/aft
line with a kluge of brass fittings, but I doubt that's any better than OEM.)
In my coach, that steel pipe is routed just as high as possible through the
frame rails, and is, of course, unclogged. At the front of that pipe, a
large (7/16" or better) hose runs UP to the filler neck, again with no low
spots which might trap fuel.
It is this system which quickly vents the air and vapors while filling the
tanks, and is supposed to spit some gas into the filler neck when the tanks
are full to shut off the nozzle, before compressed air belches a slug of
gasoline back up the fill pipe and all over the ground. Most people with
fill problems (I believe) have a partly clogged or sagged fill vent line,
which obstructs or prevents the venting of the tanks. Remember, the fill
vent line should be level or constantly uphill all the way from the gas tank
to the filler neck. (Some folks have reported that lowering the right rear
suspension while fueling allows them to fill quicker, undoubtedly by
maintaining that uphill slope.)
2. The running vent system vents vapors after the gas cap is reinstalled and
sealed. It occasionally admits air into the tanks to replace withdrawn fuel,
but the vapor pressure of the gasoline ensures this only happens occasionally
in cold weather; the rest of the time the tank is full of almost pure
gasoline vapor. (This is why many fuel-injected cars can put an electric
fuel pump, complete with sparking brushes, right IN the tank, without blowing
up. That TWA 747 that blew up over the Atlantic had an "EMPTY" main fuel tank
which hadn't been filled in months, allowing air to enter with each altitude
change and become explosive.)
Anyhow, if you are finding gas dribbling from the gas cap on the road,
it's likely the regular vent system isn't working. That system connects
fittings on the sides of each tank (2 per tank IIRC) to small (5/16"?) hoses
which lead to the left rear wheel well, hopefully uphill all the way. There,
in the highest spot which is still OUTSIDE the passenger area, they tee
together and enter the fuel separator. The separator is that mysterious
little black box with a plastic (lighter than fuel) marble inside. If more
than a half-cup of liquid fuel makes it this far, the "marble" floats in it,
and blocks off the exit from the separator, preventing liquid gas from
continuing on down the line to the charcoal canister behind/inboard the right
front wheel, where it could contaminate the canister for days, and/or drip on
the ground near the engine causing undue excitement. =8-O The fuel
separator IS available from Cinnabar, but it is unbelievably expensive, so
it's worth trying to clean yours with carburetor cleaner (the marble must
rattle freely when shaken, and you should be able to blow through it when
upright, not when inverted).
Again, sagged, clogged, kinked hoses, a blocked separator, a clogged
charcoal canister (plural in California), even a steel tube blocked with rust
(which Arch reported after diligent sleuthing), can clog this system and
force fuel out the emergency pressure-relief in the cap. And though it
really isn't meant to vent the tanks quickly, this system does allow some
vapor out when fueling, and lets everything settle down so the tanks can be
filled. BTW, once you get 50-odd gallons in, I'd suggest resisting the urge
to top up completely unless you're going out on the highway immediately and
burn some off. The system needs a little "air space" (vapor space) in each
tank to function properly. When all works properly, this is about the time
the automatic nozzle clicks off. (I have gotten around 54 gallons in mine.)
And that's the vent system, to the best of my knowledge. It's basically
simple, but it is spread out over a large horizontal area in the GMC, and
it's hard to see whether a hose is running level, uphill, or downhill, when
lying on your back with road dirt falling in your eyes. Good
luck.HTH.Rick Staples
This is as close as I can find like mine. There are two vents on each
tank. One is in the gas gauge module and uses 3/8" hose and runs to
the filler neck. The other is off to the side, is soldered into the
tank and uses 5/16" hose and runs to the module in the left wheel
well. Just trying to find out if this is plumbed
corectly.............Terry
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Terry Skinner
253-686-2624
Roy. Washington
'76 GMC
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] smog/vent? [message #74501 is a reply to message #74369] |
Sat, 20 February 2010 19:42 |
Terry Skinner
Messages: 379
Registered: January 2004
Karma: 0
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Senior Member |
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This is a quote from Gene Fisher's info from Rick.
1. There are two vent systems from each tank. The one we are most concerned
with I call the "Fill Vent" system. It consists of a fairly large (3/8"
IIRC) hose exiting from the top center of each tank, from the pickup/gauge
unit, right next to the fuel outlet hose going to the engine. This hose MUST
be routed high and steady, with no significant dips, to the steel vent pipe
which runs along the side of the coach next to the filler pipe. (A P.O. has
replaced my tee fitting where the front tank fill vent joins the fore/aft
line with a kluge of brass fittings, but I doubt that's any better than OEM.)
In my coach, that steel pipe is routed just as high as possible through the
frame rails, and is, of course, unclogged. At the front of that pipe, a
large (7/16" or better) hose runs UP to the filler neck, again with no low
spots which might trap fuel.
It is this system which quickly vents the air and vapors while filling the
tanks, and is supposed to spit some gas into the filler neck when the tanks
are full to shut off the nozzle, before compressed air belches a slug of
gasoline back up the fill pipe and all over the ground. Most people with
fill problems (I believe) have a partly clogged or sagged fill vent line,
which obstructs or prevents the venting of the tanks. Remember, the fill
vent line should be level or constantly uphill all the way from the gas tank
to the filler neck. (Some folks have reported that lowering the right rear
suspension while fueling allows them to fill quicker, undoubtedly by
maintaining that uphill slope.)
2. The running vent system vents vapors after the gas cap is reinstalled and
sealed. It occasionally admits air into the tanks to replace withdrawn fuel,
but the vapor pressure of the gasoline ensures this only happens occasionally
in cold weather; the rest of the time the tank is full of almost pure
gasoline vapor. (This is why many fuel-injected cars can put an electric
fuel pump, complete with sparking brushes, right IN the tank, without blowing
up. That TWA 747 that blew up over the Atlantic had an "EMPTY" main fuel tank
which hadn't been filled in months, allowing air to enter with each altitude
change and become explosive.)
Anyhow, if you are finding gas dribbling from the gas cap on the road,
it's likely the regular vent system isn't working. That system connects
fittings on the sides of each tank (2 per tank IIRC) to small (5/16"?) hoses
which lead to the left rear wheel well, hopefully uphill all the way. There,
in the highest spot which is still OUTSIDE the passenger area, they tee
together and enter the fuel separator. The separator is that mysterious
little black box with a plastic (lighter than fuel) marble inside. If more
than a half-cup of liquid fuel makes it this far, the "marble" floats in it,
and blocks off the exit from the separator, preventing liquid gas from
continuing on down the line to the charcoal canister behind/inboard the right
front wheel, where it could contaminate the canister for days, and/or drip on
the ground near the engine causing undue excitement. =8-O The fuel
separator IS available from Cinnabar, but it is unbelievably expensive, so
it's worth trying to clean yours with carburetor cleaner (the marble must
rattle freely when shaken, and you should be able to blow through it when
upright, not when inverted).
Again, sagged, clogged, kinked hoses, a blocked separator, a clogged
charcoal canister (plural in California), even a steel tube blocked with rust
(which Arch reported after diligent sleuthing), can clog this system and
force fuel out the emergency pressure-relief in the cap. And though it
really isn't meant to vent the tanks quickly, this system does allow some
vapor out when fueling, and lets everything settle down so the tanks can be
filled. BTW, once you get 50-odd gallons in, I'd suggest resisting the urge
to top up completely unless you're going out on the highway immediately and
burn some off. The system needs a little "air space" (vapor space) in each
tank to function properly. When all works properly, this is about the time
the automatic nozzle clicks off. (I have gotten around 54 gallons in mine.)
And that's the vent system, to the best of my knowledge. It's basically
simple, but it is spread out over a large horizontal area in the GMC, and
it's hard to see whether a hose is running level, uphill, or downhill, when
lying on your back with road dirt falling in your eyes. Good
luck.HTH.Rick Staples
This is as close as I can find like mine. There are two vents on each
tank. One is in the gas gauge module and uses 3/8" hose and runs to
the filler neck. The other is off to the side, is soldered into the
tank and uses 5/16" hose and runs to the module in the left wheel
well. Just trying to find out if this is plumbed
corectly.............Terry
> Alternator Protection Cable
> http://gmcmotorhome.info/APC.html
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Terry Skinner
253-686-2624
Roy. Washington
'76 GMC
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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