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Old 03-06-2019, 02:35 PM   #1
dlowry
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Fuel tank selector valve

I posted this several days ago, but perhaps it went to the wrong area.
I have a 1979 chevy K10 with a bad fuel tank selector valve. As everyone knows, including me, now, the 6 port single wire valve is very rare, i haven't found one, the replacement requires adding wires from the dash. Has anyone ever replaced it with a 3 port single wire valve, which are all over, online and cheap. it would require blocking the return fuel lines from the fuel pump and both tanks, no big problem. Other than reducing pressure on the needle and seat in the carb, i don't know the function of return lines, possibly emissions, i don't know.
Any help.
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Old 03-06-2019, 03:37 PM   #2
hatzie
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Re: Fuel tank selector valve

Return lines keep the fuel system from vapor locking.

Yes you can put a three port valve on. No it's not a good idea.
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Old 03-06-2019, 06:05 PM   #3
dlowry
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Re: Fuel tank selector valve

Thanks, I think i will give it a shot...not much $$ or labor involved to try.
I just installed a Holly 550 and would like to see what it does.
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Old 03-07-2019, 10:46 AM   #4
old Rusty C10
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Re: Fuel tank selector valve

this system is what you have? I have an extra set if you need parts but its been out of truck since april will need work to be usable
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Old 03-07-2019, 12:23 PM   #5
dlowry
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Re: Fuel tank selector valve

Bob, mine is completely different. It has a plastic valve housing. Thanks for the reply and offer for help.
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Old 03-07-2019, 12:35 PM   #6
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Re: Fuel tank selector valve

That's the original cable valve 73-75ish setup. If its complete I'd put it up for sale.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 03-07-2019, 01:22 PM   #7
dlowry
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Re: Fuel tank selector valve

I wish it was what i am looking for, i'd buy it.
I'm also needing a new dash and door panels for this one. I've found aftermarket on line, but lots of $$$
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Old 03-07-2019, 07:55 PM   #8
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Re: Fuel tank selector valve

unfortunately I don't have those parts I have a very nice set of 74 camper special door panels complete but nothing for 79 both my early squares needed the ones I had
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1979 Chevrolet C20 LWB
1980 Chevrolet C10 SWB
1998 Chevrolet K2500 LWB
1971 Chevrolet Monte Carlo
1966 Ford Mustang
2018 Subaru Forrester (wifes ride)
2014 Ram Bighorn SLT 4X4 Longbed Diesel
1992 Ford Superduty flatbed tow truck
2004 Dodge reg cab swb 2wd
2014 Harley Davidson Heritage Softtail


"If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board"
http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!)


PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport

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Old 03-07-2019, 08:03 PM   #9
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Re: Fuel tank selector valve

Saw one of the 6 port 1 wire valves at the OKC Pull-a-Part today. Snagged the switch as a test on my 75's gauge issues.

On a white C30 with manual transmission north of the crushing shed in case anyone wants to take a chance. Could be just as bad as OP's.
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Old 03-12-2019, 02:33 PM   #10
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Re: Fuel tank selector valve

There are a couple different things you can try. You could try using TWO of the 3-port selector valves in parallel, one for fuel, one for return. I'm not sure how much power they are pulling, but I suppose I could help you find that answer and if the wiring will handle it. But I'm 80% confident it would handle it.

The risk is if the return valve goes bad and doesn't switch, you would then be returning fuel to your opposite tank. Not the end of the world, that fuel isn't gone, but it would certainly be confusing to the NEXT owner to diagnose that problem. (I can see the thread now. "I get 12mpg out of my right side tank, but only 4mpg out of my left?!? But then my right side is magically half full again?!?")

The other option is you wire the newer style 6-port motorized valve. I've never done it, so I don't know the exact details, but the theory is simple. The old single-wire valve used one power wire and two fuel-level signal wires (three wires total). The newer style uses two power, and one signal (still three total). Some dash wiring is required, but you don't need to run new wiring all the way back to the valve, you just re-purpose one of the signal wires.
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Old 03-13-2019, 09:49 AM   #11
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Re: Fuel tank selector valve

Quote:
Originally Posted by wilkin250r View Post
There are a couple different things you can try. You could try using TWO of the 3-port selector valves in parallel, one for fuel, one for return. I'm not sure how much power they are pulling, but I suppose I could help you find that answer and if the wiring will handle it. But I'm 80% confident it would handle it.

The risk is if the return valve goes bad and doesn't switch, you would then be returning fuel to your opposite tank. Not the end of the world, that fuel isn't gone, but it would certainly be confusing to the NEXT owner to diagnose that problem. (I can see the thread now. "I get 12mpg out of my right side tank, but only 4mpg out of my left?!? But then my right side is magically half full again?!?").
I have the same valve that's gone bad in my '80. I was thinking about running the parallel 3 ports. I can't really imagine that they would pull a lot of power to just switch tanks, and it should be pretty easy just to split the power wire and run it to both valves. The passenger side tank and selector is just completely bypassed right now. I have a few other things that need done on the truck before I get to the fuel tanks, but I'll try to post back in this thread if I come up with anything useful.

I would be very grateful if anyone had some information on how to wire the newer style 6-port valve in as well.
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Old 03-13-2019, 10:44 AM   #12
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Re: Fuel tank selector valve

The motorized valve requires replacing the switch, valve, and NL2 sub-harness.
The 73-80 switch is completely different from the 81-91 switch.
The NL2 sub harness sender connection is on the RH frame rail just forward of the valve.

If you have weatherpak terminal crimping tools you can do it yourself.
Your other option is to buy a complete 81-91 dual tank sub-harness.

This is the theory of operation thread I posted... Post 1 is the early 73-80 systems post 2 is the 81-91 systems.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.
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Old 03-14-2019, 03:48 PM   #13
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Re: Fuel tank selector valve

I agree with Hatzie...no reason to re-invent the wheel or attempt to make it more round-just follow GMs’ lead on this...they already spent a lot of R&D time on it so just follow their example.
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Old 03-14-2019, 06:01 PM   #14
dlowry
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Re: Fuel tank selector valve

i replied to this once, but it didn't go thru. Anyway...I tried the newer version 6 port valve, it has a wiring diagram for the single wire application, but needs the newer style dash switch that you push to energize the valve to switch, so i went ahead and installed the 3 port valve and blocked the return lines. Right or wrong, at the moment, it is working. as far as vapor lock issues, I'm not going to be pulling heavy loads in HOT weather.
Thanks for all the help and will keep you posted on results.
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Old 03-14-2019, 08:06 PM   #15
Ryan_S
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Re: Fuel tank selector valve

Quote:
Originally Posted by hatzie View Post
The motorized valve requires replacing the switch, valve, and NL2 sub-harness.
The 73-80 switch is completely different from the 81-91 switch.
The NL2 sub harness sender connection is on the RH frame rail just forward of the valve.

If you have weatherpak terminal crimping tools you can do it yourself.
Your other option is to buy a complete 81-91 dual tank sub-harness.

This is the theory of operation thread I posted... Post 1 is the early 73-80 systems post 2 is the 81-91 systems.
http://67-72chevytrucks.com/vboard/s...d.php?t=754061
This is great information. Thank you for posting it and the link. It will be immensely helpful when I tackle my fuel tanks.
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