Duel Tank Switch Troubleshooting???

Stock FSJ Tech Area
Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Fri Sep 07, 2018 7:13 pm

I want to post this here for you guys that have a Chief or Wag that has a floor mounted duel tank switch. It would be Manual, not electric. I have the duel tanks and a switch mounted on the drivers floor back towards the seat frame. I am pulling my hair out (not much left now) trying to figure out what the heck is going on with this switch. In the position with the little 'pointer lever' pointed to the REAR of the Chief, the engine will run forever. In the position with the pointer aiming towards the passenger door the engine will run for approximately 10 minutes and run out of gas.

Now when I look underneath the Chief, my MAIN factory tank is hooked up to the inlet coming in from the passenger side on the brass body of the switch. My AUX tank is hooked to the inlet coming in from the rear. Since my gas gauge in the dashboard is reading ONLY the factory tank, I want to be able to run that tank as my primary source of gas. Seems when I switch to the factory tank ... it runs for 10 to 12 minutes and shuts down. The factory tank is FULL of gas.

What is this trying to tell me? Why run for 10 to 12 minutes then run out of fuel? Could there be a problem with the pickup in the factory tank? I replaced the fuel pump, all the fuel lines going to and from both tanks, vent lines, new filler caps included. There is NO return lines anymore since converting to edelbrock carb and removing all smog crap. I removed the electric pump to eliminate that possible source of trouble. It's running on a brand new mechanical pump ... when it runs in the one position only. I am baffled by this.

Hoping somebody with fuel delivery experience and experience with these switches/duel tanks can shed some light on what might be going on.

Thanks a lot.
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

4bz
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Joined: Wed Mar 08, 2017 12:15 pm

Re: Duel Tank Switch Troubleshooting???

Postby 4bz » Fri Sep 07, 2018 9:55 pm

When you throw the switch toward the passenger door, you are shutting off the flow of fuel to the carburetor. It takes a few minutes for the engine to consume the fuel that is in the carburetor float bowls (if you are running an Edelbrock 1406, you have two float bowls, each one serves four cylinders).

You either have a blocked line when you switch to the non-working position, or the position of the switch is not correct. If you have a see-through fuel
filter, you can watch under the hood while someone else moves the fuel valve. You will be able to see the flow of fuel through the filter when the valve is aligned correctly. As an alternative, you could also disconnect the fuel line at the inlet side of the fuel pump and blow some compressed air (about 3 psi) back through the line. When the valve is correctly routed, you will hear the air bubbling into each of the tanks.

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Sat Sep 08, 2018 5:06 am

4bz, I drove 300 miles last week with the switch pointing towards the passenger side, not a hiccup. I am going to try and by-pass the switch itself temporarily and run the main tank directly to the mechanical pump to see if it picks up fuel without shutting down. There is an in-line metal filter just forward of the switch and before the mechanical pump under the Chief. Both tanks have to flow through this filter to get to the mechanical pump, so if one of the lines is flowing gas, this tells me that the filter isn't clogged. Raining here again today so I have to wait to get under there.

Thanks for your input 4bz ... I'd like to hear from others too just to get more ideas how to work this out.

Thanks
[url=https://flic.kr/p/27D4UCk]Image
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

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tgreese
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Location: Medford MA USA

Re: Duel Tank Switch Troubleshooting???

Postby tgreese » Sat Sep 08, 2018 5:35 am

It could be connected wrong. As I recall, these switches have 3 ports in the shape of a T. The switch can be main, aux or off. Main and aux are a full 180 degrees rotation from each other. Off is half way. The path of the gas through the switch is an L. This means that the carburetor has to be connected to the down leg (upright) of the T, and each of the tanks to the horizontal ports (the cap of the T). If connected wrong the two positions at 180 degrees will be one tank to the carb, and the other direction connecting the two tanks. With the switch positioned as shown, the carb connection has to come off the side of the switch.

Both tanks must be vented, either directly to the air (usually through a vented cap) or through the vapor recovery system (charcoal canister). If either tank is not vented, when you start drawing gas from the tank, it will create a vacuum above the fuel. At some point the vacuum will be strong enough to stop the delivery of fuel, and the engine will stall from lack of fuel.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green

Fast79Chief
Posts: 109
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Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Sat Sep 08, 2018 5:43 am

Thanks Tim. I'm going to take a picture of the valve from underneath as soon as the rain stops out there. This way maybe we can verify what's what once I can show the way the P.O. mounted it under the truck. I'll try to get as much detail as I can to show the orientation of the switch to the vehicle, and to the tank lines. Thanks a lot.
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Sat Sep 08, 2018 5:47 am

I replaced the main tank gas cap with a new one a few weeks ago. It came with a rubber gasket that made it so tight of a fit that I had to take the rubber gasket off. It has a center vent hole in it anyway, so I think it would have vented well even with the gasket in place. The AUX tank filler cap is so loose a fit that I'm sure it's venting fumes. lol
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Tue Sep 11, 2018 3:36 pm

In this picture the line closest to the linkage rod (towards center of jeep) is my AUX tank. The other line is the MAIN tank, and the drop down line goes to the carb. I'm trying to figure out how the position of the lever inside the cab corresponds to the line positions?
Right now the lever is positioned front to back of the jeep. I'm not sure what line is feeding right now.

Any help with this switch is appreciated.

Thanks




Image
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

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tgreese
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Location: Medford MA USA

Re: Duel Tank Switch Troubleshooting???

Postby tgreese » Thu Sep 13, 2018 5:40 am

Seems to me that's a valve for 3 tanks, and one port is plugged. I have not seen one like that, but you can figure it out by looking at it. Inside the valve is a bobbin that connects two of the ports. That bobbin has an L-shaped path through it that connects the carb to one of the three tanks. The three tanks are 90 degrees apart from each other at the handle. With two tanks, it must be connected now with aux-main-off, and 90 degrees between each position. Did you try running at each 90-degree position of the switch?

Not that hard to take the valve down and test it on the bench. If you can't see how it works, you could make a diagram of which ports are connected at each position.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Thu Sep 13, 2018 7:16 am

Here's what I know right now without taking the switch out from under the jeep. #1. With the floor handle pointing to the rear of the jeep (as in the picture I posted) the engine runs without stop. This must be indicating the MAIN tank because it has been running that tank down according to the dash fuel gauge. #2. The lines going into the switch are: MAIN tank going into the switch inline with 'front to back'. AUX line going into switch 90 degrees from main. (see picture) If I switch the pointer lever to the AUX position the jeep will run for 10 to 12 minutes and starve out of gas. The AUX tank is not hooked to the dash gauge and does not have a sending unit. I can't even find a breather or vent line for the AUX tank. It must be relying on venting air through the loosely fitting locking gas cap. I did drive over 300 miles last week with the switch lever pointing INBOARD towards the passenger side. Something has changed since then?
My feeling is that the AUX line may have a blockage in it or the factory mechanical pump can't pull gas from the AUX tank through the switching valve? Any opinions on that would be appreciated. That's all I know right now. Got to find a solution to get the AUX tank to reliably feed gas.
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

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tgreese
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Re: Duel Tank Switch Troubleshooting???

Postby tgreese » Thu Sep 13, 2018 10:02 am

Ok, since you don't want to take the switch down, I'd suggest you connect the line from the aux tank to the line to the fuel pump and see if it will run. Take the switch out of the picture, and see if it will run on the aux tank connection.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Thu Sep 13, 2018 1:08 pm

That's a good idea Tim. Thanks. Once I verify that the mechanical pump will pull gas from the AUX tank or not ... I will have to pull the switch and see what's going on. Hate to take all the lines off just yet working on my back under it in the driveway, and worry about two tanks possibly leaking gas all over the driveway and myself. If the switch is found to be the problem, I have no problem going with a more modern electric switch that has a toggle up at the dash. Been looking at one online. I'll post a picture of it.
Image
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

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tgreese
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Re: Duel Tank Switch Troubleshooting???

Postby tgreese » Thu Sep 13, 2018 5:53 pm

Wear eye and face protection. Disposable gloves. You will get gasoline in your hair and on your skin - no way to pull those lines off without spurting out some gas. When you disconnect the hoses or the switch, gas will flow out of the hoses by gravity siphon. If I were doing this, I'd pull off the hoses and quickly plug them with a piece of dowel or whatever cylinder I could improvise. Have these ready within easy reach.

JMO - the only reason to go electric is if you want to switch both the feed and return lines. This requires a 6-port switch, not the one you show above. The 6-port electric switch will also switch the gauge between the tank sensors, so it shows the level of the tank you are connected to. If this seems more complicated than you want to get into, the manual switch is very reliable and easy to use. If you want to switch the gas gauge between the tanks, you can use a toggle switch for that.

https://www.oilybits.com/pollak-6-port- ... witch.html
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Fri Sep 14, 2018 5:47 am

Tim, all good advice. The AUX tank has NO sender/sensor or provision for a sender ... so no gauge for the AUX tank. My jeep has NO fuel return lines ... so no need for 6 position switch. The MAIN tank has the factory sender and the factory tank pickup. They are separate in 79. (Look at a 79 fuel tank diagram).
One thing I have been wondering though ... the PO has the return line fitting at the tank fuel pickup venting to the main vent at the filler neck. Since there are no metal return lines coming back to the fuel pickup at the tank, he ran a rubber vent line from what would be the return (at the tank) to the main vent at the filler neck. Could this be a problem? If I think about it, the main fuel pickup has a metal line running deep into the tank. The factory return line terminates high up on the fuel pickup ... so it being used as a 'vent' line really can't affect fuel flow. Right? Check me on this. Thanks.
Raining AGAIN today so no crawling around underneath till things dry up. In all my life I have never seen a 'wetter' summer than the one we are having here in PA. Rain every day for months. Sucks.
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)

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tgreese
Posts: 3168
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Location: Medford MA USA

Re: Duel Tank Switch Troubleshooting???

Postby tgreese » Fri Sep 14, 2018 6:11 am

Re the return line, normally it's capped if there's no return line. Sending it to the filler is not bad but does nothing. I'd have to check the '79 TSM, but I would expect a '79 to have a return line. Maybe the PO cancelled it with the carb swap, and it was more convenient to run the line to the filler than get to the top of the tank to cap the port.

Another thing to check is the condition of the hoses to the aux tank. Rotted gas line is common on cars this old, and if there's a hole in the line, the fuel pump will suck air when connected to the aux. Could explain the gradual fuel starvation you describe. The hoses in you picture look ok though.

BTW copper is not a proper material for fuel lines. Copper will work harden with vibration or even minor flexing, and crack eventually. Steel does not. Not a big issue at this point, but something to keep in mind. (Unless it's Nicopp-Cunifer line, a Cu-Ni_Fe alloy... but it's probably copper).
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 FCA Jeep Cherokee KL Trailhawk, ECO Green

Fast79Chief
Posts: 109
Joined: Wed May 09, 2018 7:10 am

Re: Duel Tank Switch Troubleshooting???

Postby Fast79Chief » Fri Sep 14, 2018 10:02 am

I put the Nicopp in from front to back both tanks, since I bought the jeep. Expensive!! What was in there was all dry rotted rubber lines. They are all removed months ago. Dont know where the factory steel lines went. I put the new Edelbrock 1406 on since I bought it. There weren't any return lines on it when I bought it ... it had an older edelbrock on it then. Appreciate you looking out for me though. This is NOT a factory setup under the hood. No pollution control, no return lines (none needed), all new vacuum lines to only necessary equipment.
Thanks.
1979 Cherokee Chief S, 360, MSD Pro Billet Distributor with Factory Ignition Box (Wow), HEI Wires, Edelbrock 1406, Edelbrock Performer manifold, 3.54 gears, Tru-Trac Locker in the rear, Turbo 400, Quadratrac, Dual tanks, new 32 x 11.50's, big winch, Homemade 2.5" full length exhaust ... and a lot of work to do. :)


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