Full Tank, No Gas

[1980 Big Ten]

'80 C10 with recently replaced left and right fuel tanks & related hardware (done by someone else). No problems when idling. When driving on a full left tank, the truck acts like it has run out of gas. When I switch to the right tank, no problems at all. Could the problem be the with the sending unit, the selector valve, the wiring, or any combination of the three? Other sources of the problem?

 

[chengny]

'80 C10 with recently replaced left and right fuel tanks & related hardware (done by someone else). No problems when idling. When driving on a full left tank, the truck acts like it has run out of gas. When I switch to the right tank, no problems at all. Could the problem be the with the sending unit, the selector valve, the wiring, or any combination of the three? Other sources of the problem?

Couple of questions that - if we knew the answers to - might help someone assist you with your problem:

1. Why were the tanks renewed, and

2. Did this condition exist before the tanks were changed?

 

[yevgenievich]

Check for kinked hoses.

 

[DanMcG]

how long does it run before it "runs out of gas"

 

[75gmck25]

On a 1980 I believe the stock location of the main fuel tank is still the passenger side tank (it moved to the driver's side in '81). This means that with no power to the solenoid valve, gas is always drawn from the passenger side tank.

It sounds like your valve may be switching to the driver's side, but switching to a tank with a plugged or missing line. If you have a six port valve, when you switch to the driver's side tank it should also switch the fuel return to that tank. The vent lines do not switch, but both vent lines should be T'd together and then run up to the vapor canister under the hood.

My guess would be that someone hooked up a vent line (or return line) to the fuel fitting on the solenoid, so when you switch to the passenger side tank you are just sucking air. Assuming you have a 3 port sending unit in the gas tank, the fuel feed line should be the largest (3/8"), the fuel return line is the smallest (1/4"), and the vent line is the middle size (5/16").

Just follow the three rubber hoses from the driver's side tank sending unit down to the metal lines that cross over the truck and then check the other end where they connect to the valve. Make sure that its all correctly plumbed.

Bruce

 

[1980 Big Ten]

Couple of questions that - if we knew the answers to - might help someone assist you with your problem:

1. Why were the tanks renewed, and

2. Did this condition exist before the tanks were changed?

Thanks for asking. This truck sat in a barn unused for about 30 years, and without having been prepped for storage. After the guy died, his son sold it to a small dealer who had to replace the tanks because the old fuel destroyed the original tanks. It looks like he also replaced the sending units and the selector valve. I don’t know if the condition existed before the tanks were changed.


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[1980 Big Ten]

how long does it run before it "runs out of gas"

It’s “run out of gas” on me three times now. The first time, I got about 10 miles down the road. The second time, 3 miles. The third time, 2 miles. After the second and third times, I opened both gas caps to even the air pressure, switched to the right tank, and fired it right up.

When it happened the first time, my right tank was empty and so I was stuck. Had a tow truck take it back to his shop. He added gas to the right tank, fired it up, and let it idle for about 20 minutes on each tank. Seemed to be fine. He diagnosed the problem as vapor lock, and said it was common on these trucks.



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[1980 Big Ten]

Check for kinked hoses.

Thank you. I’ll be sure to do that.


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[1980 Big Ten]

On a 1980 I believe the stock location of the main fuel tank is still the passenger side tank (it moved to the driver's side in '81). This means that with no power to the solenoid valve, gas is always drawn from the passenger side tank.

It sounds like your valve may be switching to the driver's side, but switching to a tank with a plugged or missing line. If you have a six port valve, when you switch to the driver's side tank it should also switch the fuel return to that tank. The vent lines do not switch, but both vent lines should be T'd together and then run up to the vapor canister under the hood.

My guess would be that someone hooked up a vent line (or return line) to the fuel fitting on the solenoid, so when you switch to the passenger side tank you are just sucking air. Assuming you have a 3 port sending unit in the gas tank, the fuel feed line should be the largest (3/8"), the fuel return line is the smallest (1/4"), and the vent line is the middle size (5/16").

Just follow the three rubber hoses from the driver's side tank sending unit down to the metal lines that cross over the truck and then check the other end where they connect to the valve. Make sure that its all correctly plumbed.

Bruce

Thank you, Bruce. The manual says that the passenger side tank is the main tank. Interestingly, it doesn’t talk at all about the optional driver’s side tank, nor does it give recommendations on how to drive with them. Now that I know, I’ll plan to drive on the main tank and only switch to the auxiliary tank when I’m running down the road and don’t want to stop right away for gas.

Thank you for the tips on checking all of the plumbing. I will certainly do that.


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[climb-101]

also check for a cracked fuel line out of the one tank that dosnt work. if the line is cracked it’s like a straw with s hole in it

 

[HotRodPC]

YES, do check the fuel lines and return lines to both tanks. My old K1500 that I no longer have had a similar problem. Turned out, that right behind the cab on the passenger side near the switching valve, I had dry rotted cracked fuel lines that were sucking air and/or leaking fuel. Replaced all the lines and problem solved and then both tanks worked too.

 

[Best truck design]

You should also check the valve that switches the fuel going to the engine I know mine failed years ago, even though the tank said it had fuel IT Didn't. It was out of gas!

It was a LONG walk.