How To Make Your Squarebody's Fuel Tank EFI-Ready

10 min read

How To Make Your Squarebody's Fuel Tank EFI-Ready

10 min read

So, you're ready to instal electronic fuel injection in your classic car or truck, or maybe you vouched for a modern engine swap. Either way, begone the days of poor reliability, cold start woes, and vapor lock. Welcome to the 21st century, where it's time to get rid of the old fuel system, which is likely lined with years of sediment, rust, and more than a few dents. You’re going to need a new high-pressure fuel pump for your EFI application, anyway.

There are two categories of fuel pumps to consider for an EFI system: in-tank and external. External fuel pumps are the cheaper option, but are noisier and more likely to overheat, potentially causing vapor lock and pump failure. An in-tank pump avoids any embarrassment caused by the noticeable harmonic hum of the external pump. Internal pumps, being submerged in fuel, also run cooler for better reliability during traffic jams, long summer cruises and track days. It’s hard to beat the smooth driving and increased reliability that an in-tank pump provides – two valuable traits for a street car to retain. And now with today’s demand for aftermarket parts, there are plenty of affordable options available that are fairly simple to install.

The Road to Reliability

Tank Conversion Chevrolet C10

Luckily, our 1986 Chevrolet C10 has lived most of its life in Arizona, and is rust-free.

You can go about installing an in-tank fuel pump one of two ways: Purchase a kit that includes a tank with a preinstalled EFI pump, or retrofit the existing OEM tank. Holley EFI conversion fuel tank kits are as close as you’ll get to a plug-and-play assembly. The included pump utilizes the patent-pending Holley HydraMat, which works as a “sump” by absorbing fuel and preventing fuel starvation in hard turns and during abrupt braking or acceleration.

Holley makes fuel pump and tank upgrades for many classic cars and trucks. In this case, an LS-swapped and slammed 1986 Chevrolet C10 pickup truck is our muse. The square body’s donor LS engine is from an ’06 GMC Sierra pickup, now controlled by Holley’s Terminator X Max engine management system.

Holley EFI tank kits, Chevrolet C/K

We opted for Holley’s Fuel Tank and EFI module combo for 1973-1987 GM C/K trucks. This kit features a 255-lph fuel pump, and because it is internally regulated, a return line is not required.

Two kits were purchased for the C10’s dual tank setup. If your vehicle has a single tank, just one kit (and half the work) is needed.

Easy As One, Two, Three...

Step One: Disassembly

The amount of time allotted to remove the fuel tank(s) is dependent on whether or not a battle with the effects of rust and corrosion occurs. Giving the vehicle a good underbody spray down beforehand will help expose bolts and tone down the falling debris.

EFI Tank Conversion old fuel line

All aged rubber fuel line should be replaced to prevent any trouble down the road.

After unfastening the electrical connectors from the switch valve and factory sending unit, we pulled the old fuel lines for an upgrade. Once you complete the above, remove the filler tube, and then unbolt and drop the tank. We used a transmission jack to support each tank while lowering it to the ground.

EFI Tank Conversion, Tank Lowered

Once the tank is lowered, the remaining wires will be accessible to clip, officially freeing the tank.

Step Two: Tank Assembly

EFI Tank Conversion, Unboxing

Unboxing each kit is admittedly satisfying. So much so that if we didn’t have to stick with just three steps, it would’ve earned an additional step all its own. Opening the boxes released a rush of new parts smells and revealed shiny new tanks and fuel pumps. Detailed, easy to follow instructions are included in each box.

EFI Tank Conversion - Instructions

The instructions included with the kit makes assembly a breeze, and if you’re more of a video visual learner, Holley’s YouTube instructional (below) makes installation virtually foolproof.

Assembling the new tank is as simple as placing the O-ring seal on the sending unit flange, dropping the fuel pump sending unit down, and then securing it with the fuel tank lock ring.

EFI Tank Conversion - Sending Unit Clocking

Make sure that your fuel sending unit is clocked correctly before locking it in place. Before bolting the tank back in, check your fuel filler hoses and replace if worn, cracked or brittle.

EFI Tank Conversion - Tank Installation

Plan on utilizing a jack or asking a buddy to assist you to make dropping and re-installing the tank easier.

Some tanks use a simple strap system. The C10 uses two tank mounting brackets that bolt onto the frame rail. One person can lift and bolt the new tanks up with the right tools, but installing the tanks is much more easily done if you can talk a buddy into lending a hand, and maybe some encouraging words.

Step Three: Feed The Machine

All EFI fuel pump setups require a fuel pump relay kit (one per pump) wired with a minimum of 12-AWG power supply wire. Stable voltage ensures the fuel pump’s performance and longevity. To run the dual saddle tanks under a square body Chevy truck, you’ll also need to install a new Pollak 6-port switch tank selector valve rated for EFI fuel pressure and an 1987-1991 GM R/V (Squarebody) dash switch.

EFI Tank Conversion - Fuel Hose

Route the fuel hose away from sharp edges and heat sources.

One reason LS Swaps are the go-to for so many gearheads is due to the engine’s performance, reliability, and availability. Running new Earl’s Vapor Guard fuel hose will make your vehicle even more dependable.

EFI Tank Conversion - Earl's Fittings

Using Earl’s fittings to connect each hose allows for ease of maintenance and adds to the build’s good looks. Earl’s flame guard insulator sleeves protect the hose in unavoidable high-heat areas.

EFI Tank Conversion - EFI Fuel System

As an additional upgrade in the quest for more power, we upgraded the OEM LS1 injectors to Holley EFI’s 48 lb/hr fuel injectors. An adapter made by ICT Billet provides enough space to install LS1-style injectors into the OEM truck manifold and fuel rail.

Note for high horsepower or turbocharged setups: Swap the kit’s sending unit for a higher flow 350lph in-tank retrofit fuel pump. You’ll also need an external billet fuel pressure regulator that is boost referenced, and a return line.

For even more detailed step-by-step instructions on how to install an in-tank fuel pump, cruise over to Holley's YouTube channel.

EFI Tank Conversion - C10 Beauty Shot


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