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Old 02-23-2010, 09:16 PM
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fuel return line - 79 chevy 1/2 ton

I am working on my 79 C-10. Originally had a 250 Inline 6, then had a 350 in it when i bought it and now I have a 454 in it. My fuel pump has three lines on it. One from the tank, one return line, and one line to the carb. However, my truck has a large line from the tank, and obviously one to the carb and then a vent line to the tank from a charcoal canister. The truck this engine came from (79 c-10 suburban, had this engine from the factory) had no emissions BS (including EGR and charcoal cannister). The charcoal cannister is on the drivers side and the fuel pump is on the passengers side. Can i just cut that line off and re-bend it to plumb in the return line for the fuel pump? I think its intended for vapors but i'm not sure. There are 5 lines total on the charcoal cannister, one to the fuel tank and the other 4 i have no idea where they go. I usually rip that thing off first thing when i get a vehicle that has it on it. I don't know if i could plumb the fuel pump return to the cannister and let it return fuel to the tank through it or what. I'm just trying to figure out something easy, it will be a b*&^# to cut and bend that line now with the engine in the truck. I didn't realize i had no return line when i had the engine out yesterday. Bleh!

I dont look forward to working in that tight space....

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Old 02-23-2010, 09:55 PM
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your going to have to keep the line for a vent as its a non atmospheric vented tank and if you use it for a return line the tank will either suck in ( if an electric pump is used , or you will get a vapor lock problem from vacume being formed in tank , leave the canister there ,the other lines are vacum timing lines to control when the canister is to be purged by emmisions controllers , also its a small diameter line not suitable for a liquid return as some have orfices in it to only let vapor thru not liquid , run a 3/8 return line to the tank its not that far of a run ( 10-15 feet of hard tube at most ) and plumb it thru the filler neck if there isn't a spare line available on the tank cover .
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Old 02-23-2010, 10:05 PM
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Quote:
Originally Posted by stimpy
your going to have to keep the line for a vent as its a non atmospheric vented tank and if you use it for a return line the tank will either suck in ( if an electric pump is used , or you will get a vapor lock problem from vacume being formed in tank , leave the canister there ,the other lines are vacum timing lines to control when the canister is to be purged by emmisions controllers , also its a small diameter line not suitable for a liquid return as some have orfices in it to only let vapor thru not liquid , run a 3/8 return line to the tank its not that far of a run ( 10-15 feet of hard tube at most ) and plumb it thru the filler neck if there isn't a spare line available on the tank cover .
If i changed the sending unit and grabbed the return line from a truck that was setup like the truck this engine was taken from, could i remove the canister then to clean up the engine bay a little? The vent I think is in the sending unit on the non emissions trucks.
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Old 02-23-2010, 10:38 PM
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the hot roders I know around here pitch the canister and get a filter from K&n for the differential vents ( a neeat little cone shaped one for a hose) and put it over the vapor pipe it as it keeps the water/mud from getting in there and the line also has a built in roll over protection unit in it from the factory , what I used to do on cars was pull the sending unit cover off the tank and unsolder the lines and then drill and put bigger lines in the holes and any return lines also went into the cover at that point ( just make sure the line goes to the bottom of the tank to prevent air bubbles and frothing in the gas tank) and then resoldered them back to the lid , a radiator shop can do the soldering if need be . Just please don't do it near the fuel tank !!
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Old 02-24-2010, 09:22 AM
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the other lines T'eed into the pvc and into vacuum manifold source, etc.,


fuel pumps changed over the years the years of when there were vented fuel caps didnt have the extra port on the fuel pumps then they started in the 70s with the chacoal canisters and adding the small extra port to the fuel pump

so use the right year and carb bbl number(2bbl or 4bbl) pump and reconnect a canister

or use a vented cap and plug the small vent line

etc.

the top of the canisters are marked at the fittings with a letter or couple letters, as to where each one goes to.

some years and engines are more complicated than others

305 ones were usually the most complicated and had the most hoses etc

especially in late 70s and all through the early mid 80s

on a 250 truck the main fuel line is 5/16" and is the biggest line on the truck for fuel related.,

on most 2bbl v-8 it was the same

and then all the 4bbl were 3/8"

this doesnt help things much either since youre gonna be using 5/16" frame line and sender unit for a 4bbl fuel pump
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Old 02-24-2010, 11:06 AM
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I checked, the 79 fuel pump also has a return line on the pump. I think the 454 trucks didnt have the emissions stuff so I am going to have to run a return line back to the tank. May have to switch out the sending units and fuel cap. I can probably get a tank and sending unit for free from a 77 C10 that had a 350 in it. If i rememebr right that truck had a return line so I can probably use that setup, but will need to run rubber line or something for the time being.

What would happen if i just capped the return line and put a clamp on it so it couldnt be pushed off. Or better yet, route the return line into a tee back into the supply line?
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Old 02-24-2010, 09:48 PM
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Quote:
Originally Posted by fast68
the other lines T'eed into the pvc and into vacuum manifold source, etc.,


fuel pumps changed over the years the years of when there were vented fuel caps didnt have the extra port on the fuel pumps then they started in the 70s with the chacoal canisters and adding the small extra port to the fuel pump

so use the right year and carb bbl number(2bbl or 4bbl) pump and reconnect a canister

or use a vented cap and plug the small vent line

etc.

the top of the canisters are marked at the fittings with a letter or couple letters, as to where each one goes to.

some years and engines are more complicated than others

305 ones were usually the most complicated and had the most hoses etc

especially in late 70s and all through the early mid 80s

on a 250 truck the main fuel line is 5/16" and is the biggest line on the truck for fuel related.,

on most 2bbl v-8 it was the same

and then all the 4bbl were 3/8"

this doesnt help things much either since youre gonna be using 5/16" frame line and sender unit for a 4bbl fuel pump
I just re-read what you wrote. A 3/8" fuel hose fits tightly on the fuel line coming from the tank on my truck so I am pretty sure it is 3/8". It appears that there are three lines on my sending unit, i can see two of them clearly when looking between the body and the cab and I see what looks like a 3rd port with a cap or something over it, but its more up under the cab so i cant see it clearly. The hoses that connect the tank to the line go up over the top of the frame, there is no room to reach up and disconnect them or the wires for the gauge. How are you supposed to drop the tank? Remove the bed first? I think i need to drop it to clean it up a little, get the old gas out of it and check the sending unit. Then ill replace with new hoses and add that return line.
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Old 02-24-2010, 11:32 PM
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the easiest way I found out from working on FI chevy trucks is to pull the bed (I saw the guys at the dealership do this ) ( if you have a engine hoist one person can do it with some h-d straps you hook them in a x from corner pocket to corner pocket and take all the slack out of them and then put the hook in the center of the x so it doesn't slide back of forth , ) or you can follow the tank straps to the end and find the nut and bolt , and ussually you wind up having to get all new straps as the taking off the bolts bend the snot out of them ( if you have time oil the bolt with penetrant every day for a weekor so before trying to loosen them so they won't get bent , that tank is heavy ( about 75 pounds empty ) and awkward .
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