Need help with fuel valve assembly on dual fuel tank 78 Chevy - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevyhubcap · 10-22-2006, 09:06 PM

I'm working on a 78 shortbed with dual fuel tanks. A previous owner apparently replaced the valve assembly at some point in the past with an incorrect valve as the vent lines were blocked off. I purchased a new valve from a GM dealer but now have a question.

The new valve is set up for 2 incoming lines from both the right and left fuel tanks one is a 5/16 the other 3/8". No problem there. It also has two out going one 5/16" and one 3/8" as well as what appears to be some sort of overflow outlet with a short piece of tubing attached to it.

I know the 3/8" outlet line goes to the fuel pump, but what about the 5/16" outlet? Where / what does it hook to?

Help appreciated

chevyhubcap

magnethead · 10-22-2006, 11:14 PM

trying to remember here..

I believe mine (a 77 longbed) has 3 3/8" ports (2 in, 1 out) and 3 1/4" ports (2 in, 1 out). the 3/8" is supply the 1/4" is return. On the tank, there may be 3 ports- the extra I am told is for TBI or carb, whichever is opposite of installed.

UncleBubba63 · 11-09-2006, 01:34 PM

Did you ever get this all worked out? Has anyone else? I could use anyone’s help on this problem.

Here is what I THINK I have figured out so far... (and would love to have some feedback from your own experience, research, etc...)

I also have a '78 with dual tanks. Engine is 350, mechanical fuel pump. I have had this truck for about 20 years. A long time ago I took off the Passenger Side tank (had a hole in it), removed the tank selector valve. With only one tank, I ran a fuel hose from the drivers side tank to the fuel line/fuel pump.

Everything has worked great for years.

Recently I decided to put another fuel tank in the Passenger side, buy a new selector valve and put it all back together.

Here is what I have so far...

I bought a fuel selector valve from NAPA. I could not remember what I took off…either a three or six port selector valve???

Their computer said the 78 called for a three port valve, and this made sense to me as my fuel pump does not have return.

The three port valve, only has one post on it... this is for the wire that runs to the selector switch in the cab (Right and Left switch). Once the wire is hooked up and the selector valve is grounded, the switch works perfectly and I can draw fuel from either tank just like in the good ole days.

NOW, here is my problem for which I am totally at a loss: NO READING ON FUEL GAUGE.

I do not know how to hook it up OR.. something is not working. I have read and read trying to find the problem but to no avail so far.

One question I have is do I even have the correct wire going to the selector valve?

It is a light green wire from the fire wall to the valve, but has a yellow wire spliced on the end that is about 10 inches long. I thought the entire wire was yellow until i peeled back the tape. Was this done at the factory or by me? I don’t have a clue…

Anyway, the selector valve works fine and does switch between the two tanks using the selector switch in the cab (by the ashtray).

So, which of the other two wires go to the Passenger side tank? The only other two wires are pink colored (but the look sort of brownish or tanish with age and dirt).

The Driver side tank has a light blue wire to the sending unit and it does not run over to the valve. It runs through the frame and up to the plug on the fire wall.

The Passenger side sending unit was missing its sending unit wire and now it is black... It is connected to the sending unit and runs over the tank, through the frame.

What do I hook that wire up to? Does it go to one of the two pink wires? Which one?

Either way, what is the other wire for? Why two pink (the brownish, tanish colored) wires?

There are only four wires total:

LIGHT BLUE to Driver’s Side sending unit.
LIGHT GREEN to ____________
PINK/WHITE to ________________
PINK to ________________________

Can anyone fill in the blanks?

I have the Light Green one on the post of the selector valve. (Which does not make sense to me, but works).

Again, why FOUR wires?

CAN ANYONE HELP ME HERE? I would really appreciate it.

Thanks,

Bubba

79BIG10 · 11-09-2006, 03:37 PM

LIGHT BLUE to Driver’s Side sending unit.
LIGHT GREEN to fuel selector valve
PINK/WHITE to The fuse panel to power the switch and power the valve when on the driver side tank
PINK to (actually tan) to the passenger side sender

infinite-foamies · 05-01-2016, 11:59 AM

Quote:

Originally Posted by 79BIG10

LIGHT BLUE to Driver’s Side sending unit.
LIGHT GREEN to fuel selector valve
PINK/WHITE to The fuse panel to power the switch and power the valve when on the driver side tank
PINK to (actually tan) to the passenger side sender

So the valve defaults to the passenger side tank? So if you lose power to the switch while driving it will run off the passenger side?

**hatzie** · 05-01-2016, 06:11 PM

Quote:

Originally Posted by infinite-foamies

So the valve defaults to the passenger side tank? So if you lose power to the switch while driving it will run off the passenger side?

1980 and prior solenoid valve systems have a default "no power" valve shuttle position.

1981 and later are motorized valve systems that retain the valve shuttle position after power is removed from the motor.

infinite-foamies · 05-01-2016, 06:17 PM

Quote:

Originally Posted by hatzie

1980 and prior solenoid valve systems have a default "no power" valve shuttle position.

1981 and later are motorized valve systems that retain the valve shuttle position after power is removed from the motor.

Thank you!

60-66 Nut · 11-09-2006, 03:57 PM

Bubba, we used to have a bunch of 76-79 Chevy duallys, all with dual tanks, but it's been a while and I can't remember the color codes. I think I remember how most everything hooks though. If your valve is working, then it has to be hooked right. The sender wires will not operate the valve. On the back of the selector switch, there should be 5 wires, 2 on one side and three on the other. On the side with 2 wires, the one in the middle should be 12V supply, and the one on the end(top or bottom-I forget) should be the wire going to your valve. On the side with 3 wires, the one in the middle goes to the gauge and the ones on each end(top and bottom) go to each sender. On trucks with only one tank, the sending unit wire is a single wire(pink I think) running from the starter wire area to the right tank. For whatever reason, on trucks with dual tanks GM chose to leave that wire and plug it to the dual tank harness at the valve. So the gauge wire has to go all the way back to the valve, just to plug to the harness and go right back to the selector switch. Just makes for more wires than necessary. If your gauge was working on the left tank before you started, then the gauge and left sender should be ok.
Hope this helps you and don't just confuse you more. Best of luck.

60-66 Nut

UncleBubba63 · 11-09-2006, 04:33 PM

Thanks guys... will put these answers to the test and report back.

One thing I have learned so far that is absolutely certain is that after 28 years of grease, dirt, grime, and time... half these wires have changed colors and if you do not pull back the tape to see what color the wires really are, you will never figure it out.

Thanks again,

Bubba

PS. HOW CAN I GET ONE OF THOSE PROFESSIONAL BEER TESTER JOBS?

60-66 Nut · 11-09-2006, 05:26 PM

[QUOTE=PS. HOW CAN I GET ONE OF THOSE PROFESSIONAL BEER TESTER JOBS?=QUOTE]

It takes many years of experience and total dedication.

60-66 Nut

boxrodz · 11-09-2006, 05:36 PM

I have a 6-port, 5-wire fuel valve on the '83.
But, I agree with you that you're probably running a 3-port valve. Since the wiring is a bit different on the pre-81s, I'll wager a guess:

Like you mentioned, it sounds like you have the wiring to switch the fuel tanks hooked up correctly. (The light green wire runs from the selector switch to the fuel valve and triggers the valve.) Each tank has a sending unit that should each have two wires. One is grounded to the frame (near the tank). The other wire is the signal wire that probably runs to the fuel valve connector. So, I think the light blue wire that is connected to the left-side tank should be disconnected and connected to the fuel valve connector. I'm guessing that this light blue wire is the run to the fuel gauge. Then, the two 'pink' wires are the signal wires for each of the sending units. So, connect one of the pink wires to the left-side sending unit and the other pink wire to the right-side sending unit. Probably the easiest way to determine which pink wire/sending unit correctly signals the fuel gauge when switched is to connect them up one way and check the fuel guage reading. If the fuel guage is reading the fuel level of the 'unswitched' fuel tank, then you need to reverse the connections.

Quote:

Originally Posted by UncleBubba63

...
PS. HOW CAN I GET ONE OF THOSE PROFESSIONAL BEER TESTER JOBS?

Quote:

Originally Posted by 60-66 Nut

It takes many years of experience and total dedication.
60-66 Nut

Sorta like Noorrrmmm over at CHEERS, eh?.

60-66 Nut · 11-09-2006, 08:12 PM

Quote:

Sorta like Noorrrmmm over at CHEERS, eh?.

Norm would be proud of me.

billie64 · 02-10-2013, 03:40 PM

i need help with my truk on the duel tanks i took them off the truck too restored the fram but i for got what side go where does the 3 outlet gos on the driverside or the 2 outlet can you all help me out on this i have a 1979 chevy short box thank you all very much

10-22-2006, 09:06 PM	#1
chevyhubcap Registered User Join Date: Oct 2006 Location: US of A Posts: 2	Need help with fuel valve assembly on dual fuel tank 78 Chevy I'm working on a 78 shortbed with dual fuel tanks. A previous owner apparently replaced the valve assembly at some point in the past with an incorrect valve as the vent lines were blocked off. I purchased a new valve from a GM dealer but now have a question. The new valve is set up for 2 incoming lines from both the right and left fuel tanks one is a 5/16 the other 3/8". No problem there. It also has two out going one 5/16" and one 3/8" as well as what appears to be some sort of overflow outlet with a short piece of tubing attached to it. I know the 3/8" outlet line goes to the fuel pump, but what about the 5/16" outlet? Where / what does it hook to? Help appreciated chevyhubcap

10-22-2006, 11:14 PM	#2
magnethead 7000 #'s of american IRON Join Date: Dec 2004 Location: north tx Posts: 883	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy trying to remember here.. I believe mine (a 77 longbed) has 3 3/8" ports (2 in, 1 out) and 3 1/4" ports (2 in, 1 out). the 3/8" is supply the 1/4" is return. On the tank, there may be 3 ports- the extra I am told is for TBI or carb, whichever is opposite of installed.

11-09-2006, 01:34 PM	#3
UncleBubba63 Registered User Join Date: Nov 2006 Location: Ft Polk, LA Posts: 3	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy Did you ever get this all worked out? Has anyone else? I could use anyone’s help on this problem. Here is what I THINK I have figured out so far... (and would love to have some feedback from your own experience, research, etc...) I also have a '78 with dual tanks. Engine is 350, mechanical fuel pump. I have had this truck for about 20 years. A long time ago I took off the Passenger Side tank (had a hole in it), removed the tank selector valve. With only one tank, I ran a fuel hose from the drivers side tank to the fuel line/fuel pump. Everything has worked great for years. Recently I decided to put another fuel tank in the Passenger side, buy a new selector valve and put it all back together. Here is what I have so far... I bought a fuel selector valve from NAPA. I could not remember what I took off…either a three or six port selector valve??? Their computer said the 78 called for a three port valve, and this made sense to me as my fuel pump does not have return. The three port valve, only has one post on it... this is for the wire that runs to the selector switch in the cab (Right and Left switch). Once the wire is hooked up and the selector valve is grounded, the switch works perfectly and I can draw fuel from either tank just like in the good ole days. NOW, here is my problem for which I am totally at a loss: NO READING ON FUEL GAUGE. I do not know how to hook it up OR.. something is not working. I have read and read trying to find the problem but to no avail so far. One question I have is do I even have the correct wire going to the selector valve? It is a light green wire from the fire wall to the valve, but has a yellow wire spliced on the end that is about 10 inches long. I thought the entire wire was yellow until i peeled back the tape. Was this done at the factory or by me? I don’t have a clue… Anyway, the selector valve works fine and does switch between the two tanks using the selector switch in the cab (by the ashtray). So, which of the other two wires go to the Passenger side tank? The only other two wires are pink colored (but the look sort of brownish or tanish with age and dirt). The Driver side tank has a light blue wire to the sending unit and it does not run over to the valve. It runs through the frame and up to the plug on the fire wall. The Passenger side sending unit was missing its sending unit wire and now it is black... It is connected to the sending unit and runs over the tank, through the frame. What do I hook that wire up to? Does it go to one of the two pink wires? Which one? Either way, what is the other wire for? Why two pink (the brownish, tanish colored) wires? There are only four wires total: LIGHT BLUE to Driver’s Side sending unit. LIGHT GREEN to ____________ PINK/WHITE to ________________ PINK to ________________________ Can anyone fill in the blanks? I have the Light Green one on the post of the selector valve. (Which does not make sense to me, but works). Again, why FOUR wires? CAN ANYONE HELP ME HERE? I would really appreciate it. Thanks, Bubba Last edited by UncleBubba63; 11-09-2006 at 01:59 PM.

11-09-2006, 03:37 PM	#4
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy LIGHT BLUE to Driver’s Side sending unit. LIGHT GREEN to fuel selector valve PINK/WHITE to The fuse panel to power the switch and power the valve when on the driver side tank PINK to (actually tan) to the passenger side sender __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

11-09-2006, 03:57 PM	#8
60-66 Nut Professional Beer Tester Join Date: Aug 2004 Location: Louisiana Posts: 453	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy Bubba, we used to have a bunch of 76-79 Chevy duallys, all with dual tanks, but it's been a while and I can't remember the color codes. I think I remember how most everything hooks though. If your valve is working, then it has to be hooked right. The sender wires will not operate the valve. On the back of the selector switch, there should be 5 wires, 2 on one side and three on the other. On the side with 2 wires, the one in the middle should be 12V supply, and the one on the end(top or bottom-I forget) should be the wire going to your valve. On the side with 3 wires, the one in the middle goes to the gauge and the ones on each end(top and bottom) go to each sender. On trucks with only one tank, the sending unit wire is a single wire(pink I think) running from the starter wire area to the right tank. For whatever reason, on trucks with dual tanks GM chose to leave that wire and plug it to the dual tank harness at the valve. So the gauge wire has to go all the way back to the valve, just to plug to the harness and go right back to the selector switch. Just makes for more wires than necessary. If your gauge was working on the left tank before you started, then the gauge and left sender should be ok. Hope this helps you and don't just confuse you more. Best of luck. 60-66 Nut __________________ 60 Ford F100 Custom Cab 61 Apache Short Fleetside 64 C10 Short Stepside 65 C80 409 V8 5spd(X-Firetruck) 83 GMC 350 Olds Diesel 85 GMC Short Bed 86 GMC Short Bed 90 GMC R3500 Crew Cab 92 GMC 1500

11-09-2006, 04:33 PM	#9
UncleBubba63 Registered User Join Date: Nov 2006 Location: Ft Polk, LA Posts: 3	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy Thanks guys... will put these answers to the test and report back. One thing I have learned so far that is absolutely certain is that after 28 years of grease, dirt, grime, and time... half these wires have changed colors and if you do not pull back the tape to see what color the wires really are, you will never figure it out. Thanks again, Bubba PS. HOW CAN I GET ONE OF THOSE PROFESSIONAL BEER TESTER JOBS?

11-09-2006, 05:26 PM	#10
60-66 Nut Professional Beer Tester Join Date: Aug 2004 Location: Louisiana Posts: 453	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy [QUOTE=PS. HOW CAN I GET ONE OF THOSE PROFESSIONAL BEER TESTER JOBS?=QUOTE] It takes many years of experience and total dedication. 60-66 Nut __________________ 60 Ford F100 Custom Cab 61 Apache Short Fleetside 64 C10 Short Stepside 65 C80 409 V8 5spd(X-Firetruck) 83 GMC 350 Olds Diesel 85 GMC Short Bed 86 GMC Short Bed 90 GMC R3500 Crew Cab 92 GMC 1500

02-10-2013, 03:40 PM	#13
billie64 Registered User Join Date: Dec 2012 Location: belding,michigan Posts: 63	Re: Need help with fuel valve assembly on dual fuel tank 78 Chevy i need help with my truk on the duel tanks i took them off the truck too restored the fram but i for got what side go where does the 3 outlet gos on the driverside or the 2 outlet can you all help me out on this i have a 1979 chevy short box thank you all very much



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