Holley Sniper In Tank Fuel Pump Install: The Complete Step-by-Step Guide

Installing a Holley Sniper in-tank fuel pump is one of the best upgrades you can make for your EFI conversion, and the good news is that you can do it yourself in a weekend with basic hand tools. This guide covers everything you need to know, from choosing the right pump module to the actual installation, wiring, and testing. Whether you're converting a carbureted car to EFI or upgrading an existing fuel system, the Holley Sniper in-tank retrofit fuel pump modules offer a straightforward, high-performance solution that supports up to 700 EFI horsepower or 900 carbureted horsepower.

What You Need to Know Before You Start

The Holley Sniper line includes two main types of in-tank pump modules: the direct-fit drop-in module for specific vehicles and the universal diecast retrofit module. The most popular option for custom installations is the Sniper Diecast In-Tank Retrofit Fuel Pump Module (part #19-350). This module fits any fuel tank between 7 and 12 inches deep and requires no welding or fabrication. It uses a 340 LPH (liters per hour) pump that is E85 compatible, and it can be rotated 360 degrees for easy plumbing and wiring.

The module is designed to work with both return and returnless fuel systems, making it ideal for Terminator EFI, Sniper EFI, MSD Atomic EFI, or any other TBI or multiport EFI conversion. The low-profile design protrudes only 1.275 inches above the tank mounting surface, so it fits in tight spaces where other pump modules will not.

Tools and Parts You Will Need

Before you start the Holley Sniper in tank fuel pump install, gather the following items:

Tools:

  • Basic hand tools: socket set, screwdrivers, pliers
  • Wire cutters and strippers
  • Crimping tool for electrical connectors
  • Marker or tape for labeling wires
  • Shop towels and a fire extinguisher (safety first)
  • A fuel pump ring removal tool or a hammer and drift (depending on your tank)

Parts:

  • Holley Sniper in-tank retrofit fuel pump module (part #19-350 for universal, or a direct-fit model for your specific vehicle)
  • Holley 12-753 30 Amp Fuel Pump Relay (recommended, not included)
  • Minimum 12-gauge wire for the power circuit
  • Fuel hose and fittings (6AN o-ring fittings are standard on the module)
  • Bypass fuel pressure regulator (Holley 12-879 or 12-880 recommended)
  • Electrical connectors, fuse holder, and fuse
  • Zip ties and hose clamps

Step 1: Prepare the Vehicle and Tank

Safety is the most important part of any fuel system work. Start by relieving the fuel system pressure. Locate the fuel pump fuse in the fuse box, start the engine, then pull the fuse. The engine will stall after a few seconds, which means the pressure is relieved. Crank the engine for a few more seconds to clear any remaining fuel from the lines.

Disconnect the negative battery cable. This prevents any sparks near the fuel system. If you are working on a vehicle with a factory fuel tank, remove the fuel tank from the vehicle. This is often easier and safer than trying to work with the tank in place. If you are using a fuel cell, make sure it is empty and clean.

Step 2: Choose the Installation Location

The Holley Sniper diecast retrofit module is designed to be installed anywhere in the tank beside your existing sending unit. The innovative clamping system allows you to position the module wherever it fits best. Mark the location on the tank where you will cut the hole for the module. The module requires a 5-inch diameter hole.

If you are using a direct-fit module like the Holley 12-345 for 1983-1997 Ford Mustangs, the module drops directly into the stock fuel tank location, so no cutting is required.

Step 3: Cut the Tank Opening (Universal Module Only)

For the universal retrofit module, use a hole saw or jigsaw to cut a 5-inch diameter hole in the top of the tank. Clean the edges of the hole with a file to remove any burrs. The module's flange has a gasket or o-ring that seals against the tank surface, so the hole does not need to be perfectly smooth, but it should be free of sharp edges.

Step 4: Install the Pump Module

The module comes with a diecast pump-hanger bracket that controls pump vibration. Slide the pump assembly into the tank through the hole. The module features a clamping system that allows you to rotate the unit 360 degrees, so you can clock the outlet and return ports to line up with your fuel lines. Once you have the orientation correct, tighten the locking ring or clamp to secure the module in place.

The module includes a filter sock, flange o-ring, and lock ring for the direct-fit version. For the universal version, you will need to use the included hardware to secure the module to the tank.

Step 5: Connect the Fuel Lines

The Holley Sniper module features 6AN o-ring outlet and return ports. Connect your fuel feed line to the outlet port and your return line to the return port. If you are using a carbureted setup, you will need a bypass regulator. Holley recommends the 12-879 or 12-880 bypass regulators for these installations. The regulator should be installed between the pump and the carburetor, with the return line going back to the tank.

For EFI systems, the return line is typically connected directly to the regulator or throttle body, depending on the system design.

Step 6: Wire the Pump

The Holley Sniper pump draws up to 16.9 amps at 13.5 volts under load. You must use a relay to power the pump. Do not run the pump directly through a switch or the ECU. Holley recommends using the 12-753 30 Amp Fuel Pump Relay along with a minimum size of 12-gauge wire.

Wiring diagram:

  • Connect the relay's power terminal (terminal 30) to the battery positive through a fuse (30 amp recommended).
  • Connect the relay's output terminal (terminal 87) to the pump's positive wire.
  • Connect the pump's negative wire to a good chassis ground.
  • Connect the relay's trigger terminal (terminal 86) to a switched 12V source, such as the ignition switch or the ECU fuel pump output.
  • Connect the relay's ground terminal (terminal 85) to chassis ground.

Make sure all connections are crimped or soldered properly and insulated with heat shrink or electrical tape. Use zip ties to secure the wiring away from moving parts and heat sources.

Step 7: Test the System

Before reinstalling the seat or access cover, test the system for leaks. Reconnect the battery. Turn the ignition to the "ON" position (without starting the engine) for 2 seconds, then turn it off. Repeat this three times to prime the fuel system. Check all fuel line connections for leaks. If you see any leaks, tighten the fittings or replace the o-rings.

Start the engine and let it idle for a minute. Check again for leaks. Listen for any unusual noises from the pump. A properly installed Holley Sniper pump should run quietly and smoothly.

Step 8: Final Assembly

Once you are satisfied that the system is leak-free and the pump is working correctly, reinstall the access cover and the rear seat or trunk trim. Take the car for a test drive to confirm the repair is complete. Monitor the fuel pressure gauge (if you have one) to ensure the pressure is within the specified range.

Common Mistakes to Avoid

Using undersized wire. The pump draws significant current. Using 14-gauge or smaller wire will cause voltage drop and reduced pump performance. Always use 12-gauge wire or larger.

Not using a relay. Running the pump directly through a switch will overload the switch and cause a fire hazard. Always use a 30-amp relay.

Forgetting the return line. If you are converting a carbureted car to EFI, you must have a return line to the tank. The pump will over-pressurize and fail without a return path.

Incorrect clocking of the module. Before you tighten the locking ring, make sure the outlet and return ports are oriented so your fuel lines will not be kinked or stressed.

Performance and Maintenance Tips

The Holley Sniper 340 LPH pump is a high-flow unit that supports up to 700 EFI horsepower or 900 carbureted horsepower. This extra capacity ensures your engine never runs lean, even under heavy load. The pump is designed for both gasoline and E85/ethanol fuel, which is important because ethanol can be corrosive to some pump materials. KEMSO uses materials that resist ethanol degradation, ensuring long-term reliability even with modern fuel formulations.

The pump is individually tested before leaving the factory, so you can be confident it will work right out of the box. Check the filter sock periodically and replace it if it becomes clogged. The service part for the strainer is Walbro 125-147, and the pump only service part is Holley 19-341.

Why Choose KEMSO for Your Fuel Pump Needs

If you are looking for a reliable, high-performance fuel pump for your next project, KEMSO offers an excellent alternative to OEM and other aftermarket brands. KEMSO fuel pumps are designed as high-performance OEM replacements that deliver over 20% more flow at 43 psi compared to stock pumps. Most KEMSO pumps support up to 200 liters per hour, significantly surpassing the original flow rate of 60-80 liters per hour. They are engineered for both gasoline and E85/ethanol fuel, and each pump is individually flow-tested before it leaves the factory.

One of the biggest advantages of choosing KEMSO is the lifetime warranty. Every KEMSO fuel pump comes with a serialized body that guarantees a lifetime warranty, which is a massive advantage over OEM and standard aftermarket parts that typically have only a 1- or 2-year warranty. KEMSO stands behind its product for as long as you own the pump.

KEMSO offers a wide range of fuel pumps for motorcycles, ATVs, UTVs, personal watercraft, and cars, covering brands like Honda, Kawasaki, KTM, Ducati, BMW, Subaru, Sea-Doo, and Can-Am. When you buy a KEMSO fuel pump, you get a complete kit that includes everything you need for installation: the pump, gradient density fuel strainers, flex hoses, Viton o-rings, wiring connectors, and clamps.

Visit KEMSO today to find the right fuel pump for your vehicle: https://www.kemsoracing.com/

Final Thoughts

The Holley Sniper in tank fuel pump install is a rewarding project that improves fuel delivery, engine performance, and reliability. The modular design makes it accessible to DIYers, and the universal fitment ensures it works with almost any fuel tank. Whether you are building a high-horsepower project or simply upgrading a daily driver, the Sniper diecast retrofit module is a smart choice.

For the best selection of KEMSO fuel pumps for your vehicle, visit https://www.kemsoracing.com/. KEMSO's promise is backed by a lifetime of confidence, giving you peace of mind for the life of your vehicle.


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