possible stuck fuel selector valve

[big_al273]

Can the Pollak 6 valve fuel selector valves become stuck between tanks drawing fuel from both tanks while still reading on the fuel gauge properly? this is in a TBI system and i seem to have been using fuel from both tanks at the same time while having the left tank selected, now i have gone under the truck and when the tank selector switch is thrown i can feel the tank selector valve cycle while it's running and both tanks register on the gauge properly but i have no way to tell yet if fuel is being taken from both tanks or not, i have filled one tank and am going to run what is left in the other then see if the full tank is still full. if anyone has dealt with this or something similar please chime in

[Irish_Alley]

take the fuel cap off and listen for the pump. i dont think you can pull from both tanks if each tank has its own pump. BUT ive noticed in my 91 v3500 ill get better mpgs with one tank vs the other. so the only thing i can think of is you may be pulling from one tank the the extra fuel isnt returning just to that tank but both or the other one. i think i had this problem before and after the cummins swap.

[hatzie]

Can the Pollak 6 valve fuel selector valves become stuck between tanks drawing fuel from both tanks while still reading on the fuel gauge properly? this is in a TBI system and i seem to have been using fuel from both tanks at the same time while having the left tank selected, now i have gone under the truck and when the tank selector switch is thrown i can feel the tank selector valve cycle while it's running and both tanks register on the gauge properly but i have no way to tell yet if fuel is being taken from both tanks or not, i have filled one tank and am going to run what is left in the other then see if the full tank is still full. if anyone has dealt with this or something similar please chime in

The way the fuel pumps are wired only on will run for each switch position.

You probably have fuel returning to both tanks.

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[big_al273]

The first issue with my selector valve had both tanks feeding fuel at the same time somehow, the second incident after i had seemingly confirmed proper valve operation was that the return port on the valve was not switching and caused an overflow situation. The next step is switching out the valve for a new Bluestreak unit as soon as i get access to the lift at work, has anyone used the Bluestreak valve instead of a Pollak unit before? any notable differences?

[hatzie]

The first issue with my selector valve had both tanks feeding fuel at the same time somehow, the second incident after i had seemingly confirmed proper valve operation was that the return port on the valve was not switching and caused an overflow situation. The next step is switching out the valve for a new Bluestreak unit as soon as i get access to the lift at work, has anyone used the Bluestreak valve instead of a Pollak unit before? any notable differences?

Are you using an aftermarket fuel pump after the valve?
There really is no way to have both in tank fuel pumps running at the same time using the factory wiring.

[big_al273]

Over the course of driving 256 miles over a weekend i started with both tanks full, i ran off of the left tank exclusively except clicking over for a few seconds to check the difference in fuel level and to test the gas gauge i didn't start doing this until the around the 130ish mile because it was still reading almost full. there was never any difference in fuel level between tanks despite only running off of the left tank and at the end of the 256 miles both tanks required the same 65 liters to get to full, so please no more "it can't happen" because it clearly did, i'm not trying to be rude but i did not post my problem to be told it can't occur. My fuel system is stock and i couldn't tell you if both pumps were running or not, but fuel was being drawn from both tanks at an equal rate without a doubt. Now i have already identified the problem part and i am going to replace it but i would still like to find out how and or why this supposedly impossible situation occurred.

[VileZambonie]

You need to validate your plumbing and wiring are truly in factory format. Also, if you don't like the advice you are receiving then simply move on.

[hatzie]

Over the course of driving 256 miles over a weekend i started with both tanks full, i ran off of the left tank exclusively except clicking over for a few seconds to check the difference in fuel level and to test the gas gauge i didn't start doing this until the around the 130ish mile because it was still reading almost full. there was never any difference in fuel level between tanks despite only running off of the left tank and at the end of the 256 miles both tanks required the same 65 liters to get to full, so please no more "it can't happen" because it clearly did, i'm not trying to be rude but i did not post my problem to be told it can't occur. My fuel system is stock and i couldn't tell you if both pumps were running or not, but fuel was being drawn from both tanks at an equal rate without a doubt. Now i have already identified the problem part and i am going to replace it but i would still like to find out how and or why this supposedly impossible situation occurred.

Your plumbing or wiring has deviated from factory original.
Validate both and you'll find your gremlin.

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[big_al273]

both tanks are plumbed too the 6 port pollak switching valve witch is plumbed to the fuel filter then the engine and to my knowledge and hands on experience with the truck so far the wiring is factory. I am dealing with a 6 port switching valve failure, the first symptom was both tanks being drawn from at the same time, the second symptom was the overflow of the right hand tank at idle due to the return side of the 6 port valve becoming jammed on the right tank while the supply, fuel pump power and gauge signal switched as intended. I will be switching out the current valve for a Bluestreak unit (hopefully tomorrow) and if anyone has used a Bluestreak 6 port switching valve instead of a Pollak unit did you notice any differences, good or bad? (the Bluestreak valve appears identical to the current valve on the truck)

[hatzie]

both tanks are plumbed too the 6 port pollak switching valve witch is plumbed to the fuel filter then the engine and to my knowledge and hands on experience with the truck so far the wiring is factory. I am dealing with a 6 port switching valve failure, the first symptom was both tanks being drawn from at the same time, the second symptom was the overflow of the right hand tank at idle due to the return side of the 6 port valve becoming jammed on the right tank while the supply, fuel pump power and gauge signal switched as intended. I will be switching out the current valve for a Bluestreak unit (hopefully tomorrow) and if anyone has used a Bluestreak 6 port switching valve instead of a Pollak unit did you notice any differences, good or bad? (the Bluestreak valve appears identical to the current valve on the truck)

Factory TBI dual tank wiring;
Uses in-tank pumps...  one in each tank.
The in-tank pumps and senders get grounds from the frame.
The motorized dual tank valve uses a polarity reversing double pole double throw switch. 
The fuel pump positive wires are wyed from the switch output wires.
With the LH tank selected the LH pump has hot and ground and the RH tank has two grounds.
With the RH tank selected the RH pump has hot and ground and the LH tank has two grounds.
Pumps only run when they have hot and ground.  If it's factory wiring you only have one pump running at a time so you'll only draw from one tank at a time.

The valve is supposed to run till the overtravel switch trips with the shuttle blocking the not selected tank lines.  If it's stuck in the middle your return will feed both tanks and you'll throttle the supply from the running pump.  Overflowing the unselected tank points to a bad valve.

The ONLY way you will draw from both tanks on a TBI truck is if you have a non factory wired fuel pump plumbed after the valve.

Standard Motor Products parts have always been good to me. 


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[bd]

Although not a common scenario, the truck could also have a faulty dash switch that is not switching cleanly.  B+ leaking through the switch to both the gray and tan fuel pump wires at the same time could power both pumps without motoring the selector valve spool through its full travel, allowing the valve spool to hang mid-position.  If you unplug the five-wire connector from the selector valve and probe the gray then tan connector wires with a test light clipped to a good clean ground, only the gray OR the tan should illuminate the test light with ignition on, depending on which tank is selected with the dash switch.  If the test light illuminates on both wires at the same time, either the dash switch is faulty or the wiring has been compromised.

[hatzie]

Although not a common scenario, the truck could also have a faulty dash switch that is not switching cleanly.  B+ leaking through the switch to both the gray and tan fuel pump wires at the same time could power both pumps without motoring the selector valve spool through its full travel, allowing the valve spool to hang mid-position.  If you unplug the five-wire connector from the selector valve and probe the gray then tan connector wires with a test light clipped to a good clean ground, only the gray OR the tan should illuminate the test light with ignition on, depending on which tank is selected with the dash switch.  If the test light illuminates on both wires at the same time, either the dash switch is faulty or the wiring has been compromised.

The valve wouldn't move in that scenario. 
The OP says the gauge is reading the correct tank when the switch is flipped. 

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[big_al273]

well got some time on the lift today and the valve is swapped out and hopefully no more issues, oh and here's the photos i took last Saturday when i did my axle seal

[LTZ C20]

I can't get over how clean that truck looks. The color, the roof lights, the running boards, tool box, even the brush guard looks good with the white and the stock hub caps. Sooo nice.