Diagram for fuel lines on a 76 K15? (2024)

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  • Jan 20, 2021
  • #1

Branktm

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K15 Sierra Grande
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Does anyone have a diagram or a reference point of where I can review how all my fuel lines go on my 1976 K15? I am in the middle of a frame off restore. and just got new saddle tanks and fuel sending units (3 outlets) in. The truck was previously set up to run off propane (new engine on order), so when i took everything off the lines were just cut and plugged. I ordered new steel fuel lines to run along the frame from LMC but there not even close to the bends of the originals i had so i am sending those back. Going to try and see how to get the minimal amount of rust the originals have in them cleaned up. But anyways my service manual is no help. What size hoses do i need to buy and how long? I got a new fuel tank selector unit as well and not 100% sure where it bolts up to.

Any help or direction is much appreciated. Cab is still off so its easy for me to route them currently. Thank you

  • Jan 21, 2021
  • #2

75gmck25

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Does your truck have a vapor canister, and are your sending units and fuel pump the 3 port version that require a return line?

My ‘75 has the vapor canister to vent the tanks, and a return line from the fuel pump. IIRC, it’s 3/8” fuel supply, 5/16” vent, and 1/4 fuel return.
- With both dual and single tanks, three metal lines run from a point near the front of the bed up along the frame rail to a point near the fuel pump.
- At the fuel pump end you have two short rubber lines over to the fuel pump (supply and return), and a rubber vent line running across under the radiator and up to the vapor canister to vent the tank.

with dual tanks
- There are three metal fuel lines that run across the rear cab bottom support between tanks. On the drivers side they connect to the 3 ports on the fuel sending unit.
- The 6 port tank solenoid is mounted on the frame rail on the passenger side. Two ports connect with short rubber hoses to the fuel supply and return lines that’s run up to the fuel pump.

I made up this diagram when I replaced all the rubber hoses on my GMC. I used all new SAE J30R9 fuel injection hose because ethanol deteriorates the old rubber. J30R7 EFI hose is a little cheaper.

Bruce

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  • Fuel system 1975 GMC.pdf

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  • Jan 23, 2021
  • #3

Branktm

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Yes it is the 3 port for the tank and the fuel pump. I dont recall a vapor canister but again it was previously converted to propane and the saddle tanks were just capped off. It had a massive tank in the bed with a line running under the cab. Thank you for the diagram. Question, the lines after the tank selector, it goes rubbed, steel, rubber then to the fuel sending unit? Seems odd how come?

  • Jan 23, 2021
  • #4

75gmck25

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The solenoid has six rubber lines connected. Three hoses run directly up to sending unit on the the passenger side tank that is right above it.

The other three rubber hoses on the solenoid could be run all the way across the truck to the other tank on the driver’s side. However, on a factory installation they instead have a bracket and 3 metal lines that run across under the truck near the back of the cab, and rubber lines on each end to connect to the sending unit and solenoid.

The metal lines running across the truck have some weird bends in them so they point the right direction and make connections easier, and if you take one off in the junkyard it’s a PIA to figure out exactly how it bolts back on on the bracket.

This is one picture, but it’s of newer style solenoid than you should have. Newer ones have a multi-wire electrical connector, but in the older ones like my ‘75 there is just one wire post on the solenoid. You can still buy the multi-wire solenoid with six ports, but the six port single wire is discontinued.

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  • Feb 13, 2021
  • #5

Branktm

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Got all my fuel hoses and clamps bought based off your diagram, got the lmc steel cross over lines all 3 of them. Planned and knocking this out today but was thrown off by 2 things. One my new tank selector valve is a 3 port not a 6. And on the vent hose you have a T that splits the 5/16 line between the tanks, what do i use for that?

  • Feb 13, 2021
  • #6

75gmck25

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You need a 6 port valve to switch both the fuel line and the fuel return line to each tank. The old-style 6 port valve with just one electrical connection is no longer available, so you can only get a 3 port in the old style.
The newer Pollack 6 port valve that has multiple electrical connections is available from several sources. I think I’ve seen an article about retrofitting the wiring so you can use a new valve on an older truck, but don’t recall where I saw it.

The tank vent lines are connected with a T, and then a metal line connects them up to the vapor canister in the engine compartment. Another alternative would be to use vented gas caps and not use the vent lines.

Bruce

  • Feb 14, 2021
  • #7

Branktm

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Ok so return the 3 port selector valve i got off lmc and get the 6 port then. Guess it doesnt matter really its not original motor anyways plus the selector valve had some uncomfortable warnings on it. Like not intended for oe replacement and offroad only.
And just find a T from any where that makes it for fuel lines i assume?

  • Feb 14, 2021
  • #8

Branktm

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K15 Sierra Grande
Engine Size
383

Also have a new painless wiring harness that is supposed to be specifically fitted for all 73-87s so i assume it should have everything to make a 6 port work

  • Feb 14, 2021
  • #9

75gmck25

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Diagram for fuel lines on a 76 K15? (2024)

FAQs

What lines connect the engine to the fuel tank? ›

Fuel lines

The lines leave the tank in a natural over/under orientation which matches the upper and lower pipes on the fuel distributor. The lower line supplies pressurized fuel to the regulator and injectors, while the upper line returns low-pressure fuel to the tank.

Which line goes to the fuel pump? ›

the line going to the pump (should be about 3/8" hose or 1/2" outside diameter) will be the feed from the tank to the pump, the other can be 1 of 2 different lines, this will depend on the emissions package and original carburetor configuration the truck was built with if this line is about 1/4" in diameter it will be ...

Why are there three lines on a fuel pump? ›

The center line is the EVAP line and it runs from the EVAP canister to the tank. The two outside lines are pressure and return lines from the fuel rail. However not all vehicles/pumps have the center line connected.

Which fuel line goes to the primer? ›

The (clear) fuel intake line runs from the top of the carburetor (straight nipple) and goes to the short post on the back of the primer bulb.

How are fuel lines connected? ›

Traditionally fuel lines had flared or compression fittings on the rigid pipe sections, and hose clamps where rubber hoses attached to metal components. In modern cars with plastic fuel lines, quick release fittings are becoming more common – this allows the fuel system components to simply clip together.

What line carries the vapor back to the fuel tank? ›

A hose used to carry fuel vapor from the fuel pump or the liquid vapor separator back to the fuel tank.

What are the two fuel lines? ›

There are only two hoses running from the pump. One is the high pressure line, which sends fuel to the injectors. The other is the return line, which dumps fuel that the injectors don't use back into the tank.

What are the two pipes in a fuel tank? ›

One hose is to alow the fuel to go into the fuel tank. the other hose is to alow the air in tank to escape alowing room for the fuel. One delivers fuel to the tank, the other delivers the gas / vapor the is displaced from the filling process through the vent hose.

Is a return fuel line necessary? ›

Does a mechanical fuel pump need a return line? No, but in situations of excessive heat, high volatility of fuel, and resulting vapor lock, a vapor return has been used by manufacturers.

What happens when fuel lines go bad? ›

When a vehicle has a broken fuel line, it develops issues with engine performance, causing problems like stalling misfires, or hard starting. In some cases, broken or leaky fuel lines can prevent your vehicle from running because of the flaws in the engine performance.

What are the few lines on fuel? ›

Fuel meaning: Meaning of fuel is a substance that is burned to provide nuclear energy, heat or power. Materials like coal, wood, oil, or gas can provide heat when burned. Methanol, Gasoline, Diesel, Propane, Natural gas, Hydrogen are types of fuel. Nuclear energy is produced by burning plutonium.

What is the return fuel line on a car? ›

The fuel return line is a hose that returns excess fuel from the engine to the fuel tank where a fuel pressure regulator is used. Fuel injection systems may or may not have return lines. Mechanical diesel fuel systems with an injector pump always have a return line that must never be pinched or clogged.

What is a fuel system without a return line? ›

A returnless-type fuel system is one that is designed to use the powertrain control module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted to the supply rail of the fuel injectors allows the powertrain control module to keep an eye on the fuel pressure.

Does fuel return line have to be smaller? ›

When designing a fuel line system for these fuels, go one and two sizes larger than the gasoline requirement. The return lines, which are the fuel lines after the regulator, can generally be one size smaller than the feed line.

Is the fuel pressure regulator on the return line? ›

For factory fuel-injected vehicles, the pressure regulator is located inside the fuel tank on a returnless fuel system. In contrast, for return-style systems, the regulator is usually in the engine compartment near the fuel rails, with the return line from the rails or regulator routed back to the tank.

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