Bryan Irons
Words and Photos by Bryan Irons
Preface: When working on any fuel system for your 4x4, the combined reaction of sparks and fuel vapours is just a recipe for disaster. If they ignite, missing eyebrows are the best-case scenario and fatal injuries are the worst-case scenario. It’s extremely important to be very cautious when working on fuel systems and all of the related components. When performing a fuel system mod or install, always complete it in a well-ventilated area and wear the appropriate protective gear and safety equipment.
We’re currently in the process of repowering our 1978 GMC C/K series half-ton pickup with some modern muscle. As we want to get as much horsepower under the hood as possible, we need to tool in an efficient fuel transferring system.
In any internal combustion engine, fuel is delivered safely from the tank to the engine. Over the last several decades, a variety of fuel systems have been introduced in the automotive market. Some worked while others burnt to the ground in a blaze of mediocrity. So, given our goal for more power and efficiency, we decided to tool a particular fuel transferring system for this project - all the while avoiding serious injury or the potential of a funeral that reeks of 91 Octane.
The original truck had a stock mechanical fuel pump system that’s driven off the engine’s camshaft. It sucks the precious petroleum from the tank and fills the carburetor fuel bowl before it’s sent to the (running) engine. This is a simple setup that operates between four and seven Psi and feeds 150 horsepower - on a good day.
The new mill we are using for the truck is a 6.0L LS Series engine with a few tweaks that you may have already read about (see 4WDrive volume 24, number 1; Can We Rebuild it: Junkyard Motor Mod Part I). As we plan to produce 450 hp at the crank, the FAST EZ-EFI fuel injection controller requires a minimum of 43 Psi. More pressure is fine, providing you know what the fuel pressure is. Luckily, we do thanks to using an inline pressure sensor.
There’s no reasonable way to run a conventional mechanical fuel pump on our modern engine, so our choice is an electric fuel pump. Two styles are commonly available, an inline fuel pump and an in-tank fuel pump. Inline pumps typically mount to the frame of the vehicle and sit at the tank or just below it.
Electric fuel pumps are great at pushing fuel but not so great at sucking it up. An in-tank pump typically requires a custom fuel cell or you may need to cut holes in the fuel tank to accommodate the pump and pickup assembly.
The advantages of an in-tank pump are multi-faceted. They operate cooler and last longer as they use the fuel in the tank as a heat sink. An in-tank pump also reduces noise levels and even protects the pump.
Our truck’s tank is relatively new and we definitely didn’t want to start butchering holes in it. Holley Performance has a series of in-tank pumps (on custom-pick assemblies) that use the existing fuel pickup assembly access hole.
They are available in a few different sizes to accommodate a variety of stock fuel tanks. Our kit was a 255 LPH pump. It’s internally regulated to 65 Psi, has a level-sending unit that works with the factory truck fuel gauge, and includes a special pickup screen that eliminates air in the fuel. Fuel outlet and vent connections are in the stock locations and the electrical connections are easy to determine on the included plug assembly.
The feed pressure of 65 Psi was just fine for our FAST controller and we plumbed the system up so we didn’t need a return line to the tank. An external pressure regulator can be used if the pressure needs to be reduced.
The special pickup screen that’s included on the fuel pickup/pump assembly is Holley’s famed HydraMat. It functions as a sheet of check valves for fuel. This means that if only one small corner of the mat is touching fuel, the fuel will be picked up through the mat. When the rest of it is exposed to air, the tank will close off. This is ideal for running crazy offroad angles, high-speed cornering and if you’re running low on fuel.
With a constant supply of gas, we needed to feed it to the engine. The factory 3/8” steel fuel lines and 5/16” vent hosing on our engine were in great shape (oddly enough) with bubble flares at the ends. However, the rubber portions wouldn’t handle the higher pressure or ethanol-based fuels.
We’ve used Earl’s Vapor Guard Hose on all of our latest projects and we had a stash of hose and clamps to plumb most of the system up to the engine, which we received from Summit Racing.
These vapour guards won’t break down with modern fuels or clog filters and injectors. They will also keep the fuel from wicking through the hose. We also had some 3/8” and 5/16” of line on hand to plumb the system. When it comes to the hard lines, it’s important to closely match up the tubing size and hose sizes. As our truck now has 10 times the fuel pressure, tightening a hose clamp as tight as you can (plus another half turn) is not a smart way to deal with flammable liquid under pressure.
The Holley fuel pump setup is prewired with a quick-connect plug and pigtail. All we needed to do now was wire up the pump and level sensor once we rerouted our wiring harness down to the tank. Holley supplies all the information needed including the wire, fuse and relay size you may need to run the pump.
Until the time comes for us to start the wiring, follow along and see how easy it is to get a classic rig ready for modern EFI.
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The main body of the Holley Muscle Truck EFI Conversion Fuel Pump (PN 12-308) consisted of a new 225 LPH pump, regulator, custom bent tubing, fuel level sender and rollover valve. That’s a lot of widgets we would have liked to figure out on our own, but it would’ve cost us more money.
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If you decide to go external for your fuel delivery needs, you’ll need three key parts. From left to right: a prefilter to ensure your pump doesn’t get damaged by debris, a fuel pressure regulator, and the fuel pump. This is a Walbro 255 LPH external pump that can be used in multiple applications.
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It’s easy to remove the entire fuel tank out of our C/K Series GM pickup, but it didn’t make sense to be a contortionist to get the old assembly out. Once it was on the floor, we used a punch to remove the locking ring.
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If we had been smarter, we would’ve run the fuel tank dry before dropping the tank. As we are not totally careless, we did empty the remaining fuel from the tank so it wouldn’t be difficult getting it back in place.
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The HydraMat material in the kit is amazing stuff. Only a small portion is required to be immersed in the fuel to work. The mat acts as a primary fuel filter. A new sealing ring and lock ring are included in the kit.
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With the assembly together and orientated correctly, it was time to get it into the tank. For our setup, the level sensor has to be temporarily unbolted.
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Now, it was just a matter of making sure the new sealing O-ring was in place and the pump assembly was aligned properly. There were indexing tabs so it was near impossible to mess it up.
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With the tanks already on the ground, we put our fuel lines on. Remember to use the proper clamps to ensure a good seal on the fittings.
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If you’re like us, you have a slew of short pieces of hose in your shop from prior projects. Keep in mind, they are not all created equal. This line is safe for modern fuel but only good for 50 Psi - not good enough for this project.
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The Earl’s Vapor Guard is good for 225 Psi of working pressure and cuts easily with a utility knife or cable shears.
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The last bit of dirty work was to wire up the pump and sending unit. Holley uses a standard ‘Weatherpak’ style connector, which made it easy to disconnect and access the tank or for troubleshooting.
Quick links:
Holley Performance: https://www.holley.com/
Summit Racing Equipment: https://www.summitracing.com/
Earl’s Performance Plumbing: https://www.holley.com/brands/earls/
FAST (Fuel Air Spark Technology): https://www.fuelairspark.com/