Ultimate fuel system guide for 73-87 C10 & K10 Squarebody trucks - LS Swaps and EFI conversions

Ultimate fuel system guide for 73-87 C10 & K10 Squarebody trucks - LS Swaps and EFI conversions

Ultimate Fuel System Guide for LS-Swapped 1973–87 Chevy/GMC Squarebody (C10, K10, Blazer)

If you’re planning an LS or EFI swap in your 1973–1987 Chevy C10 or K10 Squarebody, this guide covers everything you’ll need to build a reliable, high-performance fuel system. From tanks and pumps to hose kits, filters, and dual tank solutions—we’ve got you covered.

Fuel System Overview for LS Swaps and EFI conversions

Fuel Tanks & Sending Units for EFI and LS swaps in Squarebody Trucks

Upgrading the fuel tank is a crucial first step for an EFI or LS swap in a carbureted Square body C10, K10, or Blazer truck. Fuel injection requires a high pressure fuel pump capable of meeting the horsepower requirements of the engine.  You can utilize your existing tank and install an inline EFI capable fuel pump like the Walbro GSL392 or go with an in-tank fuel pump and updated fuel tank that features fuel baffling to prevent fuel starvation.

You have two main options for tanks if you are wanting to go with an in tank fuel pump for your LS swap or EFI conversion on your squarebody truck:

Factory fuel tank options for EFI and LS swaps

OEM 1987 Fuel Tank: 1987 was the first year of fuel injection and the last year of production for the Squarebody pickup.

This means that the factory tanks for that year are baffled and support in-tank pump sending units. These tanks will fit on any year of squarebody you are building from 73-87.

By retrofitting these baffled fuel tanks into earlier year model trucks you get a functional EFI fuel tank for a very affordable price.

For a long bed C10,K10 or other square body use the Spectra Premium GM1C fuel injection tank (20 gal, with internal baffle).

For a short bed C10,K10 or other square body, use the Spectra Premium GM11C EFI tank (16 gal, with internal baffle).

These tanks fit like stock OEM and make adding an in-tank pump easier. 

Blazer/Suburban: If you’re working on a 1973–91 K5 Blazer or R/V series Suburban (which share design with ’73–’87 pickups), Spectra offers EFI-ready tanks as well. Common options are GM15C (25 gallon) and GM14C (31 gallon) tanks with internal baffles for fuel injection.

Aftermarket EFI ready fuel tanks for C10,K10 square body

Aeromotive

18170 - Stealth 200 LPh short bed 73-81 tank, fuel pump, sending unit (stock LS engine swap or mild built EFI conversion

18470 - Stealth 340 LPh short bed 73-81 tank, fuel pump, sending unit (higher horsepower applications)

Tanks Inc

Tanks Inc. offers EFI-ready replacement tanks for 1973–87 Chevy/GMC pickups.

These tanks come with internal baffles and provisions for an in-tank pump. F

or Squarebody trucks, we recommend the Tanks Inc. models designed for your wheelbase (long bed or short bed).

When ordering, use a GPA series in-tank pump module that supports your HP (horsepower target) for a plug-and-play solution that supports typical LS swap power levels. You will also require a fuel level sending unit for these aftermarket tanks.

(See our Tanks Inc. Squarebody EFI Tanks for more details.)


Fuel Sending Units for Squarebody GM1C or GM11C OEM 87 fuel tanks

Fuel Sending Units: For any new tank, you’ll need an electric fuel sending unit (fuel pick-up assembly) that supports an in-tank pump and has the correct ports for feed and return lines:

Fuel tank sending units FG05M for drivers side and FG05N for passenger side

IMPORTANT* While these sending units will fit into an older C10,K10 square body fuel tank the tank does not have a fuel baffle which could result in pump starvation during low fuel conditions, hard acceleration, and cornering. Utilize an 87 tank with a fuel baffle for the best result. 

 

Converting FG05M and FG05N to AN fittings 

For hardline outlets on the pickup sending units (FG05M/FG05N): each unit has a 5/16″ steel return line and 3/8″ steel feed line.

Cut off the factory bubble flares on these hard tubes and be sure to keep as much material on the tube itself as possible. This is especially important on the FG05M as there is not as much material on the outlets as on the passenger side FG05N.

Install compression fittings that adapt hardline to AN6. You’ll need 1 x 5/16″ hardline to -6AN and 1 x 3/8″ hardline to -6AN adapters (one of each per sending unit).

These fittings use a ferrule to seal onto the cut tubing, creating a male AN connection for your hose ends. (We offer a Hardline Tube to AN Adapter Kit that includes both 5/16″ and 3/8″ adapters.)

Add to Cart – Hardline Tube Adapter Kit for FG05M/FG05N

 

Dual fuel tanks on Square body C10/K10 trucks

Many Squarebody C10 and K10 Pickups came from the factory with dual fuel tanks, when completing an LS swap or converting to EFI it is possible to eliminate one tank and only operate with a single tank as the fuel mileage on these systems is much improved over and old carbureted setup with a 3 speed transmission.

The fuel system is much simpler to manage with a single tank as well. 

If you decide to complete a dual tank installation then there are extra components and design factors to consider. Primarily since most EFI systems require a return line that fuel fluid flow must be directed back to the same tank it was pumped from or you will end up with one of your tanks overflowing. 

Parts needed for a dual tank fuel system on a squarebody C10 and K10 truck

Use 1987-spec sending units same as for a single tank setup now you will just need both sides. As well 1987 baffled fuel tanks will be required for both sides.

Spectra Premium FG05M (driver side) and FG05N (passenger side)

Hardline tube to AN kit for the sending units. Need QTY 2 for each side. 

Add 2× Adapter Kits to Cart

You will also require a switching valve that supports EFI fuel pressures as well as a new dash switch to both activate the pumps and change the fuel level sender to the correct side. 

Blazer & Suburban fuel tank, fuel pump, and fuel sending unit needed for LS swap and EFI Conversion

EFI and LS swap ready fuel tanks

Similar to the truck fuel tanks you will require a fuel tank with a baffle to fully support EFI and LS Swap conversions. 

GM15C - 25 Gallon fuel tank for EFI and LS swaps

GM14C - 31 Gallon fuel tank for EFI and LS swaps

GM25C - 40 Gallon fuel tank for EFI and LS swaps

EFI and LS ready fuel sending units for Blazer and Suburban fuel tanks

Match the sending unit to your fuel tank’s capacity in gallons. Like the truck sending units these will fit in the older non baffled tanks but it is not recommended due to potential fuel starvation issues. 

  • FG12K – For 25-Gallon Tanks
  • FG12L – For 31-Gallon Tanks
  • FG12M – For 40-Gallon Tanks

Needed adapter fittings for EFI ready Blazer/Suburban fuel sending units

The feed and return on the Chevy Blazer and GMC Suburban EFI and LS swap sending units are a special type of fitting that uses a small o-ring on the tip of the fitting. The adapters needed for these sending units are M16x1.5 to AN6 and M14X1.5 to AN6. 

Add to Cart – Metric M14×1.5 & M16×1.5 to AN6 Adapter Kit

 

By upgrading to an EFI-ready tank and matching sending unit, you’ll have a solid foundation for your LS swap or EFI conversion fuel system with the correct provisions for a reliable build. 

In bed tank option for square body C10 and K10 Trucks

Many guys are looking to remove fuel doors from the bedsides of their C10, K10 squarebody trucks. With some modification you can install one of the smaller size blazer tanks in between the frame rails. There are also aftermarket options for the filler including behind the rear tail light and in bed fill. 

Fuel Pumps – In-Tank Options for LS Swaps

Fuel Pump Options (In-Tank Pumps for LS Swaps)

Reliable fuel delivery is key for any EFI system including LS and LT engines.

We highly recommend using an in-tank electric fuel pump for LS swaps and EFI conversions. In-tank pumps run cooler (submerged in fuel) and are better at delivering steady pressure without vapor lock. Here are three pump options commonly used in Squarebody LS swaps, based on your engine’s power:

Spectra Premium 190 LPH Pump: A great OEM-style replacement pump, supporting up to roughly 450 horsepower. This 190 LPH pump works well for stock or mildly upgraded LS engines and for basic carb-to-EFI throttle body conversions. It’s a direct fit in the Spectra sending units. 

Add to Cart – Spectra Premium 190 LPH Fuel Pump

Walbro/TI Automotive 255 LPH Pump: A very popular high-performance in-tank pump, supporting up to about 650 HP. The Walbro 255 has proven reliability and fits the Spectra sending units without modifications. Choose this pump for moderately built engines or future power goals beyond stock. 

Add to Cart – Walbro Ti 255 LPH Fuel Pump

Aeromotive 340 LPH Stealth Pump: A higher-flow pump for extreme builds, capable of fueling 700+ HP boosted applications. The Aeromotive 340 fits the spectra EFI sending units and provides additional headroom if you anticipate major engine upgrades or forced induction. Make sure your wiring and fuel lines are up to the task if you go this route. 

Add to Cart – Aeromotive Stealth 340 LPH Fuel Pump

 

Each of these pumps is compatible with the recommended Spectra sending units.

Note: If your truck has dual tanks, you will need two fuel pumps (one in each tank). Plan on matching pumps in both tanks for balanced performance.

Inline fuel pump for LS swap and EFI conversion

Tip: While inline (external) fuel pumps can be a viable option for fuel delivery on your LS swap or EFI conversion, in-tank pumps are preferred for street-driven vehicles. If using external inline pumps they must be mounted close to the tank (they push fuel rather than pull) and will require additional considerations like a pre-filter and protection from heat.

For simplicity and reliability, an in-tank setup is the way to go for your Squarebody LS swap.

The best option for inline fuel pumps on your LS swap or EFI conversion on your square C10 or K10 is the Walbro GSL392. 

 

Add to Cart – Walbro Ti 255 LPH Inline Fuel Pump

AN Fuel Hose Sizing and Routing for LS Swap and EFI conversion for your C10 or K10 

Fuel Lines and Hose Kits – Feed & Return Basics

Upgrading to EFI means you’ll also need new fuel lines that can handle high pressure (58+ psi) and modern fuel blends (e.g. ethanol).

We recommend using Hot Rod AN LLC PTFE-lined AN hose for all fuel plumbing in your LS swap. PTFE (Teflon) hose has several advantages: it’s impervious to gasoline and ethanol (no smell or degradation), it handles high pressure and heat, and it lasts much longer than rubber EFI hose. All our fuel system kits use PTFE-lined AN hoses and PTFE AN fittings for leak-free, safe performance. Feed and Return Line Length: For a typical Squarebody truck, the following lengths of AN hose are needed:

LS fuel line swap kits

Return-Style Systems: Approximately 25–27 feet total hose to run both a feed line and a return line from the tank(s) to the engine. Our 30 ft hose bundle is the most popular choice to ensure you have enough length for a clean routing on a long-bed pickup. This covers feed and return with some extra for slack or re-routing as needed.

Return-Less (Single line) Systems: Approximately 20 feet of hose is sufficient when running a single feed line (no return from the engine bay, return line from fuel pressure regulator only). In practice, we suggest our 20 ft PTFE hose kit if you mount the regulator/filter near the tank. If you mount the regulator further forward, you might need a bit more length (up to ~24 ft). Our 30 ft kit can also be used if you prefer to have extra hose on hand.

AN Hose Size: We use -6 AN size PTFE hose for both feed and return in LS swaps. -6 AN has an inner diameter of 0.320", which is sufficient for up to 650HP on an LS fuel system.

The return line also uses -6 (which is actually larger than a stock return on some systems, but ensures no restriction). For almost all LS swaps up to ~650+ HP, -6 AN feed/return is sufficient.

Only extremely high output builds (or fuel systems running E85 at high flow) might consider -8 AN for the feed line, but that’s rarely necessary for the typical swap.

Transmission Cooler lines

If planning to run Hot Rod AN LLC's AN PTFE hose and AN fittings for your transmission as well as fuel a 40 foot hose kit is typically sufficient, although every install is different so be sure to measure before ordering so that you have enough PTFE hose to complete your build. You will require additional PTFE hose ends, appropriate transmission adapters, and potentially adapter fittings for your transmission cooler and radiator to complete the plumbing install. 

AN PTFE Hose and AN Fitting Kits including LS fuel line swap kits: 

To make things easy, we offer complete AN hose bundles that include PTFE hose and matching AN fittings. Our LS Swap kits also include mounting clamps for AN PTFE hose and EFI quick connect fittings to connect to the engine. Return-less kits also include the Corvette regulator and filter to easily complete your LS swap.

You can choose the appearance that suits your build:

Nylon Braided PTFE Hose Kits – Lightweight black nylon outer braid for a subtle OEM-style look.

Stainless Steel Braided PTFE Hose Kits – Classic steel braid for maximum abrasion resistance (can be kept raw or covered with loom).

Colored Nylon Braided Hose Kits – Nylon braid in various colors or patterns (e.g. black with colored checks) for a custom look.

Each bundle comes with enough hose and a variety of hose-end fittings (straight, 45°, 90° as needed) to plumb your fuel system. Our Return-Style LS Swap Fuel Line Kit and Return-Less LS Swap Kit include all the hoses and adapter fittings specific to those setups (more on these kits below).

Filters and Regulators: Return vs. Returnless Systems

One of the key differences in LS swap fuel systems is whether you run a return-style system (two lines, with a built in regulator) or a return-less system (single feed line, with regulation handled near the tank or at the fuel unit). Let’s break down what you need for each type:

Return-Style LS Swap Fuel System

A return-style system uses a regulator built into the LS engine fuel rail to maintain pressure, sending excess fuel back to the tank via a return line.

Many early LS engines (and most aftermarket EFI conversions) require a return line. For example, if you’re running a Holley Sniper EFI or FiTech EFI throttle-body on a classic engine, those systems have an internal regulator but still require a return line to bleed off excess fuel.

Some Gen III LS engines (like LS1 from F-body cars or truck engines when using certain intake setups) also used return lines and an engine-mounted regulator.

Factory OEM Inline fuel filter for return-style LS fuel systems and EFI conversions

Filter: In a return-style setup, you need a high-pressure inline fuel filter placed between the pump and the engine (typically along the frame rail). We recommend a 10 micron filter to protect the injectors (10µ is the typical rating for EFI filters). You have a few options:

Factory-Style Inline Filter: The most popular choice is our factory OEM-style metal canister fuel filter. These filters are rated at ~5 micron and have Metric threaded ports M16x1.5.

With the right AN adapter fittings, you can easily integrate one into your AN fuel hose system. This approach is cost-effective and makes future replacements easy (order replacement elements when you order your kit). 


Aftermarket inline fuel filter options for return style or high horsepower LS swaps and EFI conversions

Holley Inline fuel Filter (10 micron, replaceable element): Holley offers a billet inline filter that takes a replaceable 10µ element. It has ORB (O-ring boss) ports which we convert to AN6 using adapter fittings. If you prefer a serviceable filter, this is a great option. You’ll need two ORB-8 to AN-6 adapters for the Holley filter (since its ports are 8AN O-ring). We carry these adapters and the Holley filter unit.

 

Aeromotive Inline Fuel Filter with build in AN fittings (10 micron, high flow): Aeromotive’s inline filter is another excellent choice, especially for higher horsepower builds. It features built in AN fittings that link directly with our fuel line kits.

The Aeromotive filters are built for racing and high flow, ensuring minimal pressure drop. 

Add to Cart – Aeromotive AN6 10 Micron Inline Filter

Regardless of which filter you choose, mount it securely to the frame rail or under the cab, away from heat and moving parts. Ensure the flow direction is correct (most filters have an arrow indicating flow).

Fuel pressure regulator for LS swap and EFI conversions

Regulator:

In a return-style system, the fuel pressure regulator may be:

Integrated in the engine’s fuel rail (some stock LS rails have a built-in regulator and return outlet), or

A separate unit mounted near the engine (common in aftermarket EFI where you mount an adjustable regulator on the firewall or engine bay).

If your LS engine or EFI system doesn’t have a built-in regulator, you’ll need to add one.

Set it to 58 PSI for most LS injectors (this is the standard pressure for GM LS-based engines). Many aftermarket regulators have two outlet ports (for dual feeds or feed/return) and one return port.

You’d run your feed line from the pump into the 10 micron fuel filter and into the regulator, then out to the engine, with the return port running back to the tank.

Alternatively and recommended in higher horsepower boosted applications you can run the fuel pressure regulator after the fuel rail with each rail entering the regulator and a single return line back to the tank. In this setup the fuel filter would be placed before the fuel rails. Y adapter fittings are often used in this type of layout. 

Our Return-Style LS Swap Hose Kit includes the necessary hoses and fittings from the tank’s sending unit up to the fuel rail. However, a regulator itself is not included in that basic kit (since some customers use the regulator on their engine or part of their EFI system). If you need a standalone regulator, we have those available separately be sure to select a regulator compatible with your system. 

Shop Now – Fuel Pressure Regulators

 

Return-Less (Corvette-Style regulator) LS Swap Fuel System

Many later-model LS engines and swaps are set up as “returnless” – meaning only a single feed line goes to the engine, and fuel pressure is regulated near the tank. The most common way to implement this is using the famous Corvette-style filter/regulator unit. This device, originally used on C5 Corvettes, combines a fuel filter and regulator into one. It has three ports:

A 3/8″ feed line inlet from the pump (unfiltered fuel in),

A 5/16″ return line outlet back to the tank (excess fuel out),

A 3/8″ outlet that goes forward to the engine (filtered, regulated fuel out).

The Corvette filter/regulator automatically maintains ~58 PSI and sends excess fuel back to the tank via the return port. It simplifies the plumbing since you can run a single line up to the engine. We include this unit in our Return-Less LS Swap Kit, as well our corvette regulator includes built in male AN6 fittings to easily hook it up to our AN PTFE hoses.

When installing the Corvette-style regulator, mount it close to the fuel tank – usually on the frame rail area near the rear of the truck. This keeps the return line short and ensures the fuel in the long line to the engine is always at constant pressure. Be careful with the ports: one common mistake is mixing up the feed and return on the regulator.

Important to Remember:

The center port (5/16″ size) on the filter/regulator is the return going back to the tank.

The 3/8″ port on the outer edge (often marked with an arrow or “Flow” indicating out) is the feed from the pump into the filter/regulator.

The 3/8″ quick-connect fitting on the top (center of unit) is the regulated output that goes to your engine’s fuel rail.

If you accidentally connect the lines incorrectly (for example, hooking the pump feed to the wrong port), you will get very high pressure readings or no pressure, and the system won’t function correctly.

Follow the diagram or markings on the regulator. Our Corvette Filter/Regulator Unit with AN Adapters comes pre-configured with AN6 male fittings on all three ports, making it straightforward to attach your -6 PTFE lines.

No additional inline filter is needed with this setup, since the unit’s internal filter (around 4–5 micron) handles the fuel filtration.

Note: Some aftermarket EFI solutions (like certain FiTech Go EFI units) can be run returnless by using a built-in regulator and blocking a return, but in most cases we recommend sticking to either the Corvette unit or running a full return system.

The Corvette filter/reg is a proven OEM-quality solution for returnless LS swaps.

EFI conversions Holley Sniper, Fitech, ACES Efi

EFI Conversions (Holley Sniper, FiTech, etc.)

If you’re converting an older carbureted engine to EFI using a throttle-body injection system (like the Holley Sniper, Terminator EFI, FiTech, Edelbrock Pro-Flo, etc.), your fuel system needs are very similar to an LS swap.

The key difference is where the regulator is: Many TBI-style EFI units (Sniper, FiTech) have an internal regulator and require a return line while others require an external fuel pressure regulator.

Essentially, follow the recommended installation for your throttle body EFI conversion kit:

Built in regulator for Throttle body efi conversion kits

The EFI unit will have a return port that you plumb back to the tank (it regulates pressure internally and dumps excess fuel out this return).

You still need a fuel filter on the feed line (10 micron recommended, before the throttle body unit). Most aftermarket EFI kits include some fittings that are AN-compatible, so you can often use our standard hose kit and simply add a filter.

Our 30 ft PTFE Hose Bundle is perfect for an EFI retrofit on a carbureted engine, as it gives you enough hose for feed and return. Pair it with one of the 10 micron filters mentioned above (OEM-style, Holley, or Aeromotive) and you have everything you need aside from the tank, pump, and sending unit discussed earlier. In summary, an EFI conversion fuel system looks just like a return-style LS swap system: in-tank pump, feed line, filter, then to EFI unit, and a return line back to tank.

Other needed items

Other Parts & Tools You’ll Need

Up to this point, we’ve covered the major components: tank, pump, lines, filter, regulator. There are a few additional items and tools that will make your install easier and more professional:

AN PTFE Fuel hose installation tools and instructions

Fuel Hose Cutter: PTFE-lined hose is tough stuff, and cutting it cleanly is important. Use a dedicated hose cutting shear or a sharp cut-off wheel to get a straight, fray-free cut on your AN hose. We carry an affordable AN Hose Cutter tool that works great for PTFE braided line – it ensures a clean cut without flattening the hose.

AN Hose Assembly Tools: When installing reusable PTFE hose end fittings, it helps to have aluminum vise jaw inserts and an AN wrench set.

The aluminum vise jaws hold your fittings securely without scratching the anodized finish, and the aluminum wrenches let you tighten fittings snugly without damaging them. These tools will prevent marring your new fittings and make assembly much easier. (Check out our AN Fitting Vise Jaws and Aluminum AN Wrench Set in the tools section.)

 

Squarebody C10, K10 dual tank installation

Fuel Tank Selector Valve (for dual tanks): If your truck has dual fuel tanks (a common option on long-bed pickups), you’ll need to address the switching mechanism for EFI.

The factory carbureted dual-tank setup used a 6-port selector valve to switch feed lines (and also switched the fuel gauge sending unit inputs).

For an EFI swap, you must use a valve designed for fuel injection pressure. We recommend the 1987 GM style 6-port fuel selector valve (Standard Motor Products part # FV5 or equivalent). This valve can handle high pressure and also switches the return lines, ensuring that each tank returns fuel to itself. We’ll detail the dual-tank plumbing in the next section.

Dual Tank Switch (electrical): Along with the valve, you need a dash switch that can control two fuel pumps (one for each tank). The 1987 EFI trucks used a dual pole, double throw (DPDT) switch that simultaneously switches the valve and powers the selected tank’s pump. A commonly used replacement is DS283 (dual tank fuel pump selector switch) or an equivalent toggle available through aftermarket. This switch will allow you to toggle between tanks, and it should handle the pump current or trigger pump relays accordingly.

Electrical Relay and Wiring: It’s highly recommended to wire your fuel pump (or pumps) using a properly rated relay and adequate gauge wire. The factory wiring (especially on older trucks) may not be sufficient to carry the 8–15 amps a high-output fuel pump can draw.

Use the ECU’s fuel pump trigger or ignition-on signal to activate a relay, which then supplies battery power to the pump through a fuse. For dual pumps, you can either use two relays (one for each pump controlled by the dash switch), or route the dash switch output through one relay. The important thing is to ensure each pump gets solid 12V power without voltage drop – this keeps the pump running at full speed and your fuel pressure consistent.

With these tools and extra parts on hand, you’ll be equipped to tackle the installation smoothly. Next, we’ll walk through some installation best practices for assembling the system on your 73–87 Squarebody truck.

Fuel Line Installation Best Practices

Fuel System Installation Steps & Best Practices

Now that you have the right parts, let’s go over the installation process step-by-step. A careful installation will save you headaches and ensure your LS swap or EFI conversion runs flawlessly.

1. Install the In-Tank Pump and Sending Unit

Start with prepping your fuel tank and sending unit assembly:

Mounting the Pump: If your fuel pump isn’t already installed on the sending unit, now’s the time to attach it. The Spectra sending units we listed are designed to accept the recommended pumps (Spectra, Walbro, Aeromotive) with little or no modification. Follow the instructions provided with the sending unit to secure the pump onto the hanger. Make sure to use the supplied fuel hose or filter sock as directed. The pump’s pickup (sock) should sit near the bottom of the tank without being blocked.

Modify Hard Line Outlets: As mentioned earlier, cut off the bubble flares on the steel hard lines of the sending unit (the 3/8″ and 5/16″ tubes). Use a tubing cutter or a fine hacksaw and make a clean cut just behind each flare. Deburr the cut ends. Install the compression hardline-to-AN6 adapter fittings onto each tube (follow the fitting instructions: typically, slide the nut and ferrule on, then tighten the fitting onto the tube to crimp the ferrule). Tighten until the ferrule is seated and the fitting is snug – this creates a leak-free seal. Now you have male AN-6 connections for feed and return coming off the sending unit.

Vent Tube: Your sending unit likely has a smaller third tube for the tank vent/rollover valve. Do not cut or cap the vent tube – it’s needed to let your tank breathe and allow fuel expansion. If you plan to run a charcoal canister or a vent line to the filler neck, keep this tube intact. You can also attach a vent filter or check valve if doing a custom vent. (Some builders convert the vent to AN as well, but it’s not typically necessary unless you’re routing a long vent line.)

Install Sending Unit in Tank: With pump and fittings in place, install the sending unit into the tank. Use a new tank gasket or O-ring to prevent leaks. Ensure the locking ring (or screws, depending on tank design) are secured properly. Double-check that the pump wiring is fed through and sealed (many sending units have a pass-through for the power/ground wires). It’s a good idea to test the fuel level sender with an ohmmeter at this stage (move the float to ensure the resistance changes) before sealing it up.

Dual Tank EFI Setup for 73–87 Squarebody

Fuel Tank Installation: If your tank is out of the truck, now is a good time to put it back in. Make sure the tank straps and pads are in good shape. It’s easier to run new fuel lines with the tank loosely mounted or even removed, but final tightening of bolts can be done later. Safety note: Work on the fuel tank in a well-ventilated area and have a fire extinguisher nearby. Avoid open flames or sparks when working with fuel components.

2. Mount the Filter and/or Regulator

Depending on your system type, you will now mount the inline filter and possibly the regulator:

Return-Style: Mount your inline filter along the frame rail between the tank and engine. A common location is on the inside of the frame rail, roughly below the driver’s seat area (where it’s protected and accessible). You can use cushioned clamps or a filter bracket to secure it. If your filter is a metal canister type with quick-connect ends, this is where you’ll attach the AN adapter fittings on each side. Make sure the flow arrow on the filter points toward the engine. You generally won’t mount the regulator back here – if using an engine-mounted regulator, you’ll handle that in the engine bay (or if your fuel rail has a built-in regulator, it’s already in place).

Return-Less: Mount the Corvette-style filter/regulator near the tank. Many builders bolt the regulator to the frame rail kick-up at the rear, or to a bracket off the tank strap bolt area. Ensure the unit is oriented so you can plumb the lines without sharp kinks. Remember the port orientation: side port (3/8") from the pump, center 5/16" return back to tank, and the 3/8" quick-connect on the end will point forward (to the engine). If your regulator unit didn’t come with AN adapters pre-installed, install the quick-connect to AN6 fittings now: one in the 3/8" outlet that goes to engine (if not already AN), and possibly one on the return if needed. Our Hot Rod AN regulator comes with those adapters built-in, simplifying this step.

Filter Brackets: If using a billet filter or the Corvette unit, consider using a proper clamp or bracket to hold it securely. Vibration can stress the lines or cause fatigue if the filter/regulator is just hanging by the hoses. Many aftermarket filters have specific mounting clamps available. Secure mounting also makes future service (filter changes) easier.

Plumbing at the Tank: Connect short hose segments from the tank sending unit to the filter/regulator if it’s very close. For instance, from the sending unit’s feed (AN-6 male) to the inlet of the filter/reg (AN-6 male) you’ll use a hose end on each side. If the span is just a few inches, you might need to loop a slightly longer hose to avoid a tight bend. Using a 45° or 90° hose end at the sending unit can help route the hose inward toward the frame smoothly. The same goes for the return line into the sending unit’s return port. Plan your hose end angles such that the hoses run neatly without sharp bends or contact with the frame or body.

3. Run the Fuel Feed Line (and Return Line)

Next, route your AN hoses from the rear (tank area) up to the engine bay:

Routing Path: The factory fuel line usually ran along the inside of the frame rail on the passenger side for these trucks. You can follow a similar path with your new lines. Ensure the lines are inside the frame rail or otherwise protected from road debris and exhaust heat. Avoid routing near sharp edges or moving parts. If you have to pass through a frame opening, use a grommet or bulkhead fitting to protect the hose.

Securing the Lines: Use line clamps or zip-ties at regular intervals (about every 12-18 inches) to secure the hose to the frame. PTFE hose is fairly rigid, so plan for gentle bends and avoid forcing it into a tight radius. If you need to make a 90° turn, it’s often better to use a 90° hose end fitting there rather than bending the hose sharply. This looks cleaner and maintains flow.

Heat Shielding: If any section of hose runs near the exhaust (headers, downpipes, etc.), consider adding a heat sleeve or reflective heat wrap on that segment. Maintaining cool fuel temperature helps prevent vapor lock and extends pump life.

Engine Bay Connections: For the feed line, you’ll terminate at the engine’s fuel rail or carb/EFI unit:

On an LS engine fuel rail, if it’s a stock rail with a quick-connect inlet, use a 3/8″ EFI quick-connect to AN-6 adapter to connect your AN hose to the rail. (Most LS rails from 1999+ are female quick-connect; earlier LS1 rails might be a threaded fitting.) Our kits include the necessary adapter for the LS rail connection.

On a Holley Sniper or aftermarket EFI, you might have an AN fitting already (Holley Sniper often has an EFI/ORB port that can take an AN adapter). Check the EFI unit’s inlet size; many include -6AN male fittings or 9/16-18 threads that adapt to AN6.

Tighten all connections and double-check the O-rings in any quick-connect fittings (lightly lube them before inserting).

Return Line (if applicable): Route the return line from the engine bay (if from a regulator or EFI unit) back alongside the feed line to the tank area. The return line will connect to the sending unit’s 5/16" AN adapter (or to the return port on the Corvette regulator for returnless setups). The same routing rules apply – secure it well, keep it protected. Important: Make sure the end of the return line inside the tank (integral to the sending unit) is submerged or directed downward. The Spectra sending units handle this by design. A properly routed return will prevent fuel aeration (bubbles) in the tank.

4. Dual Tank Considerations

If your Squarebody has dual tanks, the plumbing is a bit more complex but very doable with the right parts. Here’s an overview of how to set up dual tanks in an EFI LS swap:

Two Sending Units & Pumps: Install an EFI sending unit and in-tank pump in each tank (use Spectra FG05M and FG05N for left/right, or the appropriate models for your setup). Do all the steps for modifying each sending unit with AN adapters as described above. Both tanks will have feed and return AN connections coming off them.

Outlet Hose Ends: It’s common to use 90° or 45° hose ends right at the sending unit outlets to immediately turn the hoses inward and run them along the frame. This prevents the hoses from sticking out where they could be snagged or crushed. Choose the angle that best lines up with the path into the frame rail. The goal is to minimize bends and get the hoses running along the frame as cleanly as possible. Every truck may be a bit different; take your time to mock up the routing. If you run into clearance issues with body mounts or exhaust, reach out to our help desk – we can assist with alternate fitting choices.

Fuel tank selector valve and dash switch

Fuel Tank Selector Valve: Plumb both tanks’ lines to a 6-port switching valve (e.g. Standard FV5). This valve will have six hose connections:

2 inlet ports for fuel coming from each tank’s feed line (3/8″ lines from left and right tank).

2 return ports for fuel going back to each tank (5/16″ return lines to left and right tank).

1 outlet feed port that goes forward to the engine (3/8″ out to filter/regulator).

1 inlet return port that comes from the regulator back into the valve (5/16″ returning fuel from engine side).

The valve essentially acts as a gate that simultaneously switches both the feed and return to whichever tank is active. Important: Use the EFI-rated valve (for 87+ pressurized systems). Carbureted (older) switching valves will not have provisions for return, or may not handle the pressure.

Connecting AN to the Valve: Most factory-style selector valves (including the FV5) have plastic barbed fittings for hose, not AN threads. You cannot directly attach AN hose ends to these plastic barbs. The solution is to use short lengths of EFI-rated rubber fuel hose as couplers:

Slide a short piece (a few inches) of 3/8″ EFI hose onto each of the valve’s 3/8″ feed barbs (two inlets from tanks, one outlet to engine).

Likewise, attach short pieces of 5/16″ EFI hose to each 5/16″ return barb (two outlets to tanks, one inlet from regulator).

Secure all hoses to the valve with fuel injection hose clamps (use the clamps designed for EFI hose – they provide even pressure without cutting into the hose).

Now, on the free ends of those short rubber hoses, you can use brass hose barb to AN adapters to transition to your PTFE lines. For example, for a 3/8″ rubber hose end, use a 3/8″ barb to -6AN male adapter; slip the hose over the barb and clamp it, and now you have a male AN fitting to connect your PTFE line’s female end. Do this for each connection:

Left tank feed -> 3/8″ rubber -> 3/8″ barb-to-AN fitting -> PTFE hose from left tank.

Right tank feed -> 3/8″ rubber -> barb-to-AN -> PTFE hose from right tank.

Valve outlet feed -> 3/8″ rubber -> barb-to-AN -> PTFE hose going forward to engine.

And similarly for the 5/16″ return lines on each side.

We offer packs of hose barb to AN6 adapters for exactly this purpose (both 5/16″ and 3/8″ sizes). Using these ensures you can integrate the selector valve without leaks.

Mounting the Valve: Mount the selector valve on the frame rail or crossmember near the cab where the factory one was (usually driver side frame under the cab) – it should be reasonably central so hose lengths from each tank are about even. The valve has an electrical connector as well – this will tie into your dash switch.

After the Valve – Filter/Regulator: Downstream of the valve, you will have a single feed line running to the engine. This line should go into your filter (if return style) or into the Corvette regulator (if returnless) just as with a single-tank setup. The only difference is that the return from the regulator will go into the selector valve’s return inlet, which the valve will direct to the correct tank. If using the Corvette filter/regulator, its return port goes to the valve (not directly to a tank’s sending unit). If using a return-style system with a regulator up front, run the return line from the regulator all the way back to the selector valve’s return inlet.

Electrical Wiring for Dual Pumps: The dual tank selector switch (DS283 or similar) will have multiple terminals to control both the valve and the pumps. Typically, one pole of the switch toggles the valve (directing which tank is active) and the other pole toggles power between Pump A or Pump B. Wire it such that only the pump in the currently selected tank gets power. You will likely still use a relay setup: e.g. the switch triggers a relay which sends power to the selected pump. The switch also ensures the fuel gauge reads from the correct sending unit (this is usually handled through the same switch or a separate circuit in the valve). Follow a wiring diagram for a 1987 dual tank setup as a reference – it’s very similar.

Setting up dual tanks is a bit more work, but once done, you’ll retain the extended range of two fuel tanks with a modern EFI fuel system. Many C/K truck enthusiasts successfully run dual EFI tanks using the above method. Just remember to always use components rated for fuel injection pressure for safety and reliability.

Final Checks and LS/EFI engine startup

5. Final Checks and Initial Startup

With all hardware installed and plumbed, do these final steps before firing up your LS engine or EFI system:

Tighten and Inspect: Ensure every AN fitting, adapter, and clamp is tight. Do not overtighten AN fittings – snug plus a quarter turn is usually enough (with aluminum wrenches). Overtightening can damage flares or O-rings. Verify that the hose ends are properly assembled (no PTFE liner visible outside the fitting, no twisted hose).

Fluids and Wiring: Add a few gallons of fuel to the tank(s). Reconnect the battery (if you disconnected it during install). Double-check your fuel pump relay and wiring connections. If dual tanks, make sure the selector valve and switch are wired correctly.

Priming the System: Turn the key to the “ON” position (or trigger the ECU to prime the pump) to power the fuel pump without starting the engine. The pump should run for a few seconds and build pressure. Check for any leaks at all connections. This is critical – if you find a leak, turn off the pump and fix it before proceeding. Common leak points might be a loose hose end or an adapter not quite seated right. Address any issues and try again until the system holds pressure with no leaks.

Check Fuel Pressure: If you have a fuel pressure gauge, connect it to the Schrader valve on the LS rail (if present) or to any test port. You should see around 58 PSI (for LS engines) when the pump is running. For carb EFI units like Sniper, you might see a lower pressure if they regulate internally (Sniper usually regulates around 58 psi as well). If pressure is way off, something may be plumbed incorrectly (e.g. regulator connections) or the pump may be not getting proper voltage.

Initial Start: Once everything checks out, start the engine. It may crank a bit longer on the first start as the fuel lines purge air and fill with fuel. Once running, inspect all hoses again under the higher pressure of a running system. Check the fuel pressure regulator (if adjustable) and set it to the desired pressure. Verify that the engine is idling smoothly and the EFI system is getting fuel properly.

Routing and Safety: As a final note, ensure the fuel lines are not rubbing on anything once the truck is back on the ground. Suspension travel and engine movement can change clearances. Make sure lines have slack where needed (engine to frame connections should have some flex – that’s where flexible hose is used vs. hard line). Use zip ties or additional clamps to secure any loosely hanging sections.

Congratulations!

If you’ve followed along, you have successfully installed a high-performance fuel system in your Squarebody truck that will support your LS swap or EFI conversion for years to come. Our PTFE hose and quality components will ensure you have OEM-level reliability with the capability to feed high-horsepower engines.

Frequently Asked Questions

Frequently Asked Questions (FAQ)

Q: What fuel pressure do LS engines require?

A: Nearly all modern LS engines run at 58 PSI (4 bar) fuel pressure. This is the target pressure set by the regulator (whether it’s the Corvette filter/reg or an in-rail regulator). Some aftermarket EFI systems also run around 58–60 psi. Always verify the requirement of your specific fuel injection system, but 58 psi is the general rule for GM LS-based injectors.

Q: Do I need a return line for my LS swap?

A: It depends on your fuel system setup. If you use a returnless system (with a filter/regulator near the tank or an in-tank regulator), you will only run a single feed line to the engine – the return from the regulator goes back to the tank at the rear. Many later LS engines (and swap kits) use this style. However, if your engine or EFI conversion has a regulator on the engine (or requires a return), then yes, you’ll run a feed and return line (return-style). Examples that need return lines include using an adjustable regulator on the engine, or throttle-body EFI kits like Holley Sniper (which has an internal regulator but requires a return line to dump excess fuel). In summary: returnless = one line to engine; return-style = two lines (feed and return).

Q: Can I use the factory fuel hard lines from my carbureted truck for the LS swap?

A: It’s generally not recommended. The original carb fuel lines (especially on older trucks) were not designed for high pressure. They are often 5/16″ lines, which are undersized for high horsepower EFI, and they may have rust or internal varnish. Additionally, old lines likely aren’t rated for constant 60 psi and ethanol-blended fuels. For safety and reliability, install new EFI-rated fuel lines. Our PTFE AN hose kits are a great solution, but if not, at least use new steel or nylon lines rated for EFI. If you attempt to re-use the stock hard line as a feed, you’d still need to add a return line for EFI and contend with making new connections – so it’s usually easier to start fresh with the proper hose.

Q: What’s the benefit of PTFE fuel hose over regular fuel hose? Will I have a gas smell in my garage with your PTFE hose? 

A: PTFE (Teflon) hose has a core that is impervious to fuels and additives. It won’t deteriorate or leach chemicals over time, meaning no fuel smell seeping through the lines (common with rubber hoses). PTFE hose is also able to handle much higher pressure and temperature. In contrast, regular rubber EFI hose (even the high-pressure SAE 30R9 type) can slowly degrade with ethanol and will eventually sweat fuel odor. PTFE lines last much longer and are the choice for performance and longevity. The only slight downside is PTFE hose is a bit more rigid and requires specific PTFE-compatible fittings – but our kits include everything you need to make assembly straightforward.

Q: Can I use an inline fuel pump for my EFI conversion or LS swap into my squarebody?

A: You can, but it’s not usually the best choice for an EFI swap on a street-driven vehicle. Inline pumps push fuel well but are not great at suction, so they must be mounted low and near the tank outlet. They tend to be louder and can run hotter since they aren’t cooled by fuel like in-tank pumps. If you do use an inline pump, make sure to also install a pre-filter (to protect the pump from tank sediment), and be aware that if the truck runs low on fuel or the pump is higher than the tank, you could get fuel delivery issues. In-tank pumps, by contrast, prime easily, run cooler/quieter, and generally last longer. For those reasons, we recommend converting to an in-tank pump setup using the parts outlined above, especially since products like the Tanks Inc. modules make it relatively simple.

Q. Should I run dual tanks or a single tank on my LS swap or EFI conversion?

A: Dual tanks add complexity, but the solution is to mimic the factory 1987 dual-tank EFI setup. You will use two in-tank pumps and sending units (one per tank), a 6-port selector valve that switches both feed and return, and a dual tank switch to control it all. We described the process in detail above. Key points: use the correct EFI-rated switching valve (so it routes return fuel and handles pressure), run AN lines from each tank to the valve (with short rubber sections at the valve connections), and wire the dash switch to only power the pump for the selected tank. When done properly, you’ll be able to toggle between tanks just like stock, and the system will supply your LS engine with uninterrupted fuel from either tank.

Q: What is a Corvette fuel filter/regulator and why is it used in swaps?

A: The term “Corvette regulator” refers to the combination filter/regulator unit originally used on the C5 Corvette (1997-2004) and some other GM vehicles. It’s a single canister that maintains ~58 psi fuel pressure and returns excess fuel, while also filtering the fuel. In LS swap applications, it’s popular because it simplifies the fuel system – you can run a single line to the engine and don’t need a separate regulator up front. It’s especially handy when retrofitting fuel injection into older vehicles. By mounting this unit near the tank, you essentially convert a return-style system into a returnless one. Our return-less LS swap kits include this filter/regulator because it’s a proven, cost-effective solution. It saves plumbing a full-length return line to the engine bay, and replacements are readily available at parts stores if ever needed.

Q: My swap is just a mild 5.3L – do I really need all these AN fittings and fancy hoses?

A: You might not need high-end performance parts for a stock engine, but using quality hoses and fittings is cheap insurance. Even a stock 5.3 or 6.0 LS requires a reliable 58 psi fuel supply. Our PTFE hose kits and fittings ensure you won’t have fuel leaks or vapor smell, and they future-proof your truck if you later modify the engine for more power. Many builders have tried to cut corners by using rubber lines or hacking together OEM parts, only to later deal with leaks, cracked hoses, or insufficient flow. By doing it right the first time – with the proper tank, pump, filters, and lines – you’ll have a safe and dependable fuel system. Plus, our AN plumbing looks great and is often more straightforward than adapting old parts. In short, even for a mild build, we recommend investing in a proper EFI fuel system setup.

Q: Where can I find the parts listed in this guide?

A: We’ve made it easy by linking many items directly to our product pages above (see the internal links in each section). Hot Rod AN specializes in fuel system plumbing, and we carry complete LS swap fuel line kits (return and returnless), PTFE hose bundles, Corvette style regulators, Spectra sending units, AN adapter fittings, fuel filters, EFI pumps, and all the tools and accessories you’ll need. You can browse our website or use the links provided to find the exact parts. If something isn’t listed on our site (such as the OEM tanks or the selector valve), we’ve noted the part numbers so you can source it. And of course, you can always contact us if you need guidance on what to order.

Conclusion to our squarebody C10,K10,Blazer, and Suburban LS swap and EFI conversion guide.

By following this guide, you should have a clear roadmap for upgrading your Squarebody Chevy/GMC truck’s fuel system for an LS engine swap or EFI conversion. Internal links throughout this article point you to our recommended products available on HotRodAN (HotRodFuelHose) for a one-stop shopping experience. We hope this write-up has answered your questions and set you up for success with your project. If you have any further questions or need personalized advice, don’t hesitate to reach out via our Contact Us page or email. Our team is always happy to help fellow enthusiasts tackle their fuel system upgrades with confidence. Good luck, and enjoy the improved performance and reliability of your LS-swapped Squarebody C10, K10, Blazer, or Suburban!

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