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

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

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

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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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

If you use the new 6 port valve, this looks like really useful information.
http://products.pollakaftermarket.com/Asset/42-159 IS_41-revdd.pdf

Bruce