Home » Public Forums » GMCnet » Tanks are out, mechanic not happy (Random power loss, no cause found yet.)
| Tanks are out, mechanic not happy [message #352433] |
Wed, 26 February 2020 17:16  |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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I was expecting to find crushed, collapsed, or old, vacuum collapsible hose to account for the random power loss. No such luck...Now I will have to dig into the fuel tanks, which I guess I was going to do anyway. But now the possibilities have been narrowed down to the filter socks or pickup tubes in the tanks,or the device in the wheelwell that looks maladjusted.
Apparently, someone has been here before. The fuel lines are 30R7 and still flexible enough to disconnect without damage. The vent lines were stiff, the front tank filler neck hose snapped the paper thin nylon tee by the frame before I could get to the clamp even with my 18 inch extension. That hose would not have let go of that tee anyway  The filler neck vent hose barb on that tank is also apparently the fuel leak when I fill the tanks and it drips out in front of the rear wheel for the first few hundred feet.
http://www.gmcmhphotos.com/photos/fuel-system/p67071-fill-pipe-26amp-3b-vent-tee.html
This the top of the rear (Main) tank
http://www.gmcmhphotos.com/photos/fuel-system/p67074-rear-tank-top.html
All ins and outs accounted for except the one with a bolt clamped in the stubby hose on the side. Generator feed is the right angle fitting at corner, red capped port on top goes to filler neck vent. Sending unit has engine feed and canister lines. Anybody know what was the original purpose of the port closed off by the hose and bolt?
There is also a device in series with the rear tank vent line that is located in the LR forward wheelwell,don't have a pic of that yet, but even though the tank has 2 vents I wonder if it is the cause of the power loss. I think it's a gravity sensor to close the line between the tanks in case you remain on a steep angle for a long enough time. I'm going to perform some tests on it and get a pic to post in a reply once the workload clears.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Tanks are out, mechanic not happy [message #352434 is a reply to message #352433] |
Wed, 26 February 2020 18:44  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Terry,
Since you have gone this far, cost of hoses is not much and get the
correct large hosed from the GMC Vendors as they will hav the ourrect.
Also replace the vent lins going to the Vapor separator and the
separator at the same time.
Possibly the cap might be defective as well.
Iknow you understand all that, but when we play with these most of the
time, we get little smart.
Give me a call so we can exchange info and resolve your issues.
On Wed, Feb 26, 2020 at 3:17 PM Terry via Gmclist
wrote:
> I was expecting to find crushed, collapsed, or old, vacuum collapsible
> hose to account for the random power loss. No such luck...Now I will have to
> dig into the fuel tanks, which I guess I was going to do anyway. But now
> the possibilities have been narrowed down to the filter socks or pickup
> tubes
> in the tanks,or the device in the wheelwell that looks maladjusted.
> Apparently, someone has been here before. The fuel lines are 30R7 and
> still flexible enough to disconnect without damage. The vent lines were
> stiff, the front tank filler neck hose snapped the paper thin nylon tee by
> the frame before I could get to the clamp even with my 18 inch extension.
> That hose would not have let go of that tee anyway :lol: The filler neck
> vent hose barb on that tank is also apparently the fuel leak when I fill the
> tanks and it drips out in front of the rear wheel for the first few
> hundred feet.
>
>
> http://www.gmcmhphotos.com/photos/fuel-system/p67071-fill-pipe-26amp-3b-vent-tee.html
>
> This the top of the rear (Main) tank
>
> http://www.gmcmhphotos.com/photos/fuel-system/p67074-rear-tank-top.html
> All ins and outs accounted for except the one with a bolt clamped in the
> stubby hose on the side. Generator feed is the right angle fitting at
> corner,
> red capped port on top goes to filler neck vent. Sending unit has engine
> feed and canister lines. Anybody know what was the original purpose of the
> port closed off by the hose and bolt?
> There is also a device in series with the rear tank vent line that is
> located in the LR forward wheelwell,don't have a pic of that yet, but even
> though the tank has 2 vents I wonder if it is the cause of the power loss.
> I think it's a gravity sensor to close the line between the tanks in case
> you remain on a steep angle for a long enough time. I'm going to perform
> some tests on it and get a pic to post in a reply once the workload clears.
> --
> Terry Kelpien
>
> ASE Master Technician
>
> 73 Glacier 260
>
> Smithfield, Va.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Tanks are out, mechanic not happy [message #352436 is a reply to message #352433] |
Wed, 26 February 2020 21:09 |
Green machine
Messages: 184
Registered: July 2019
Location: North Vancouver BC
Karma: 5
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Senior Member |
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Jim will answer any questions you may have better than I can but so you can stop scratching your head, at least for tonight, that extra port is not factory.
Shawn Harris
North Vancouver,
Canada
1977 Palm Beach 403
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| Re: Tanks are out, mechanic not happy [message #352438 is a reply to message #352436] |
Wed, 26 February 2020 23:59 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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While the tanks ought to be re-hosed if they have not been done in a long time as your problem could be there. I really suspect you fuel starvation problem is one of sucking fuel rather the pushing fuel from the tanks to the engine.
The original design by GM was not the best. They used a mechanical suction pump mounted on the engine to draw fuel a long way from what I will call "remote mounted" tanks. It worked most of the time but with the reformation of gasoline since the 1970 and the addition of ethanol blended gasoline with the EPA 1.0 RVP waver to the gasoline companies for ethanol diluted fuel we have a potential problem waiting to happen. Modern vehicles do not suck gas from the tanks to the engine. They push the gasoline from the tanks to the engine and usually at much higher pressure than a carb engine can use.
So I am suggesting that you add an additional pump back near or inside the tanks to move fuel, under pressure, forward to the engine. The pump can be an on demand one using a switch inside, or can be run full time with the appropriate shut off circuit.
Some people have eliminated the mechanical pump completely and installed two electrical pumps. One at each tank. Others have left the mechanical pump installed and only added the electrical pump on the aux tank. So when the engine is stumbling they can simply select aux and turn on the boost pump using the same switch.
So go ahead and re-hose, but also consider installing a boost pump if you do not already have one.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Tanks are out, mechanic not happy [message #352441 is a reply to message #352433] |
Thu, 27 February 2020 07:59 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Here's how I did it on my carbureted 23" :http://www.gmcmhphotos.com/photos/g6198-cane-9-creek-rv-park-heflin-2c-al.html
* The Mr. Gasket pumps have an internal check valve, you don't need an external one.
* The supplied filters fail at the swaged seam, discard them and get the Wix exact replacements.
* You can use an oil pressure switch and the hot on start terminal of the starter solenoid or a Ford impact/rollover switch for safety.
* Blank flange the mechanical pump opening and screw a barbed adapter on the hard line to the carburetor for the pump flex line.
* Cap the tank selector valve and use the original hoses. This allows a return to stock quickly if you wish.
After the install I had no further vapor lock problems with the coach.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Tanks are out, mechanic not happy [message #352449 is a reply to message #352438] |
Thu, 27 February 2020 13:08 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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The P.O. already installed an exterior pump and eliminated the fuel valve, and I added a solenoid shutoff valve to eliminate the possibility of drawing air from the front tank while going up a long grade. Hose to front and engine pump replaced. Bought new engine pump but have not installed it yet as these type of pumps do not come back to life once they fail. Interesting story of the 30R7 installation, and I have a new full roll of 30R6 to replace the hoses with. Made in USA, it's rated for alcohol, but so was/is the 30R7. Using in on other vehicles too. Is that going to be bad in 4 years?
So what's the deal with the hosery? Greenie weenies making us use water-based hose? Matt said get 30R14, but how long is that going to last with whatever ends up being supplied to us as fuel? What about my 7 non-alcohol gasoline fueled vintage vehicles with whatever that fuel is composed of? I can just see the scenario of the old school fuel dissolving the inside of the new school hose happening to me, as I have BTDT a few times in the past. Thought I had this deal covered with the new 30R6 hose, but now starting to wonder.
Matt, that extra plugged off line still looks like a backyard fix to me, can't believe GM would do that... 
I'll bet the problem is going to be the device in the wheelwell, since I don't know what its function is yet.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Tanks are out, mechanic not happy [message #352450 is a reply to message #352449] |
Thu, 27 February 2020 13:31 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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The device in the wheel well is part of the vent system going to the charcoal canister(s) up front. It is a float valve that shuts off the vent line if gasoline gets into it. That device is called a vapor separator and is mounted up high so gasoline should not normally get into it. It if does then the valve shuts off the line to the canister(s).
I guess it is possible if that valve stuck closed that you could develop a vacuum in the tank as you drive, but really that line is suppose to vent fumes the opposite direction away from the tank. I do not know about pulling air back in to the tank in the opposite direction. If this is the problem it would be easy to prove. When it is failing, just let air in by loosening the filler cap.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Tanks are out, mechanic not happy [message #352452 is a reply to message #352449] |
Thu, 27 February 2020 13:26 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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Senior Member |
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Ah, the vapor/fuel separator
https://corvetteparts.com/item/valve-fuel-vapor-separator-1971-1974
Also good at separating dollars from your wallet.
Dolph
DE AD0LF
Wheeling, West Virginia
1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission
“The Aluminum and Fiberglass Mistress"
> On Feb 27, 2020, at 2:08 PM, Terry via Gmclist wrote:
>
> The P.O. already installed an exterior pump and eliminated the fuel valve, and I added a solenoid shutoff valve to eliminate the possibility of
> drawing air from the front tank while going up a long grade. Hose to front and engine pump replaced. Bought new engine pump but have not installed it
> yet as these type of pumps do not come back to life once they fail. Interesting story of the 30R7 installation, and I have a new full roll of 30R6 to
> replace the hoses with. Made in USA, it's rated for alcohol, but so was/is the 30R7. Using in on other vehicles too. Is that going to be bad in 4
> years?
> So what's the deal with the hosery? Greenie weenies making us use water-based hose? :lol: Matt said get 30R14, but how long is that going to last
> with whatever ends up being supplied to us as fuel? What about my 7 non-alcohol gasoline fueled vintage vehicles with whatever that fuel is composed
> of? I can just see the scenario of the old school fuel dissolving the inside of the new school hose happening to me, as I have BTDT a few times in the
> past. Thought I had this deal covered with the new 30R6 hose, but now starting to wonder.
> Matt, that extra plugged off line still looks like a backyard fix to me, can't believe GM would do that... :?
> I'll bet the problem is going to be the device in the wheelwell, since I don't know what its function is yet.
> --
> Terry Kelpien
>
> ASE Master Technician
>
> 73 Glacier 260
>
> Smithfield, Va.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: Tanks are out, mechanic not happy [message #352456 is a reply to message #352433] |
Thu, 27 February 2020 14:54 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Quick and dirty test.. take the saparator off the wheel well and shake it - rattle? OK. No cracks in the plastic? OK. Silent? Get another onwe or open that one and correct the problem.
--johnny
Sake me I rattle, squeeze me....
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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