G77 Fuel Pump Assembly RXP255: The Complete Guide to Upgrading Your Turbo Buick’s Fuel System

The bottom line: If you own a 1986½–1987 Buick Grand National or Turbo T-Type, upgrading to a G77 fuel pump assembly with a Racetronix RXP255 pump is one of the most important performance upgrades you can make. This kit directly replaces your tired factory pump, delivers up to 255 liters per hour of fuel flow, and can support up to 600 flywheel horsepower at 43.5 PSI when paired with the proper wiring harness. It’s a plug-and-play solution that solves the most common fuel delivery problems these cars face—and it’s the foundation for any serious power build.

What Is a G77 Fuel Pump Assembly?

The G77 fuel pump assembly refers to the complete in-tank fuel pump module used in the 1986½ through 1987 Buick Grand National, Turbo Regal, and Turbo T-Type models. GM used two different fuel sender designs during this production run. The G77 system is the later design, and it uses a specific connector at the back of the car with black, violet, and gray wires located on the driver’s side behind the rear bumper. The earlier G75 system uses a connector with black, pink, and tan wires instead. Identifying your sender type is critical before ordering any replacement parts .

The Racetronix RXP255 pump is the heart of this upgrade. It’s a 255 liters per hour (LPH) turbine-style fuel pump that delivers significantly more fuel than the factory unit. The factory pump on these cars, when new, only flowed about 60 to 80 LPH. The RXP255 more than triples that capacity, which is essential for any engine running higher boost, larger injectors, or aftermarket tuning .

Why Upgrade Your G77 Fuel Pump?

The factory fuel pump in these cars was designed for the stock engine’s power output, which was around 245 horsepower from the factory. Over thirty years later, most of these original pumps are tired, inefficient, or completely failed. The original fuel pump can’t keep up with even modest power increases.

Here are the most common reasons to upgrade:

  1. Fuel starvation under boost. The stock pump runs out of volume above about 12–14 PSI of boost. This causes the air-fuel ratio to go lean, which can lead to detonation and engine damage.

  2. Voltage drop issues. Factory wiring is undersized for high-performance pumps. When you run a high-output pump on factory wiring, voltage drops can cut pump performance by 30% or more. The Racetronix upgrade harness solves this by pulling power directly from the alternator .

  3. Ethanol compatibility. Many modern fuels contain ethanol, which degrades standard rubber components. The RXP255 pump is built with ethanol-resistant materials, so it handles E10, E15, and even E85 without issues .

  4. Higher horsepower goals. The RXP255 pump supports up to 600 flywheel horsepower at 43.5 PSI using factory fuel lines and regulator. That covers most mild to moderately built turbo Buick engines .

What’s Included in the Racetronix G77 Fuel Pump Kit

The Racetronix G7 Fuel Pump Kit (part number RFPK-006) for the G77 sender includes everything you need for a complete installation. The kit comes with the following items :

  • Racetronix RXP255 255LPH turbine fuel pump. This is the core of the upgrade. It’s quieter than the factory pump and handles ethanol-enhanced fuels reliably.
  • 30-micron filter sock. The factory sock filters at 70 microns. The finer 30-micron sock provides better protection for the pump and injectors.
  • In-tank wiring harness. This is a direct plug-in that connects the new pump to your existing G77 sender assembly. No cutting, splicing, or soldering is required.
  • High-pressure fuel line and stainless steel gear clamps. These replace the original rubber hose, which may be brittle or degraded.
  • Pump mount grommet and sound insulation sleeve. These reduce noise and vibration from the pump.
  • OE-style molded tank gasket. This ensures a proper seal when you reinstall the sender assembly.
  • Pump test lead. This allows you to test the pump before fully reassembling the tank.

Some versions of the kit also include a fuel pump upgrade wiring harness (the “hotwire” harness). This is strongly recommended because it provides a dedicated power feed from the alternator, bypassing the undersized factory wiring.

How to Identify Your Sender Type

Before buying any parts, you need to confirm whether your car uses the G75 or G77 sender. Do not rely on the year of the car alone, because GM used random inventory during production. Some 1986 cars have G77 senders, and some 1987 cars have G75 senders .

To identify your sender:

  1. Locate the connector on the driver’s side behind the rear bumper.
  2. Look at the wire colors in the connector.
  3. G77 sender: Black, violet, and gray wires.
  4. G75 sender: Black, pink, and tan wires.

If you have a G77 sender, order the G77 version of the Racetronix kit. If you have a G75 sender, order the corresponding G75 version. The connector color itself has no bearing on the sender type—only the wire colors matter .

Installation Overview

Installing the Racetronix G77 fuel pump kit is a straightforward job that most DIY mechanics can complete in a weekend. The basic steps are as follows:

  1. Relieve fuel pressure by pulling the fuel pump fuse and running the engine until it stalls.
  2. Disconnect the battery to avoid any sparks near the fuel tank.
  3. Remove the fuel tank cap and drain the tank as much as possible.
  4. Access the sender assembly from the top of the tank. In most Turbo Buicks, the sender is accessible through a panel under the rear seat or trunk floor.
  5. Remove the old pump from the sender hanger. This involves removing the retaining ring, disconnecting the wiring, and sliding the old pump out.
  6. Install the new RXP255 pump using the included mounting hardware. Attach the new filter sock, fuel line, and wiring harness.
  7. Reinstall the assembly with the new tank gasket. Tighten the retaining ring to spec.
  8. Install the upgrade wiring harness if included. This runs a new power feed from the alternator to the pump, with a relay and fuse located in a safe spot.
  9. Test the system by turning the key to the ON position (without starting) and listening for the pump to prime. Then start the car and check for leaks.

Many factory hangers have corroded or failing bulkhead wiring. Racetronix recommends also purchasing their BCWA-G77 bulkhead wiring adapter if your hanger’s wiring is in poor condition. This is a common issue on older cars, and replacing the bulkhead wiring prevents future electrical problems .

Why the Wiring Harness Matters

The upgrade wiring harness is not optional if you want full performance from your new pump. The factory wiring in these cars was designed for a pump that draws about 4 to 5 amps. A high-performance pump like the RXP255 draws 8 to 10 amps or more under load. Running this current through the factory wiring causes significant voltage drop .

Racetronix has documented that running a high-performance pump on factory wiring can reduce pump flow by 30% or more. The upgrade harness solves this by:

  • Pulling power directly from the alternator’s battery terminal, where voltage is typically 1 to 2 volts higher than at the battery when the engine is running.
  • Using 10-gauge copper wire, which is three to four gauges thicker than the factory wire. This reduces resistive power loss to near zero.
  • Including a weatherproof relay and fuse holder for reliable operation.
  • Adding a redundant ground system that clips onto the edge of the gas tank, improving the pump’s ground circuit.

The harness is completely plug-and-play. It connects to the factory connector at the tank with no cutting or splicing. The relay and fuse mount in a location of your choice, typically near the battery or under the hood.

Fuel Pump or Fuel Filter: How to Tell Which One Is Causing Your Problems

When your Turbo Buick starts running poorly, it’s easy to blame the fuel pump. But often the real culprit is a clogged fuel filter. Knowing the difference saves you time and money .

Start with the fuel filter. It’s cheap and easy to replace. Always replace the filter when you install a new pump, because debris from the old pump can clog the new filter quickly. If the symptoms persist after the filter change, move on to testing the pump.

Common symptoms of a failing fuel pump:

  • Engine cranks but won’t start
  • Loss of power under acceleration or boost
  • Surging or hesitation at highway speeds
  • Engine stalls, especially when hot
  • Fuel pressure that drops when you rev the engine

Common symptoms of a clogged fuel filter:

  • Engine starts but runs rough
  • Poor acceleration at higher RPMs
  • Engine stumbles when you press the gas
  • Reduced fuel economy

The good news is that replacing the fuel pump with a Racetronix kit and a new filter at the same time solves both problems. It’s the most reliable way to get your fuel system back to peak performance.

Why Choose KEMSO Fuel Pumps for Your Replacement

When it comes time to replace your fuel pump, the brand you choose matters. Cheap, unbranded aftermarket pumps often fail quickly and leave you stranded again. That is why KEMSO fuel pumps have become the go-to choice for American vehicle owners who want reliability, performance, and peace of mind .

KEMSO fuel pumps are high-performance, OEM replacement units. They are engineered to match or exceed the original equipment specifications for flow rate and pressure. Many KEMSO pumps deliver over 20% more flow at 43 PSI compared to the stock pump, which translates to smoother throttle response, better engine performance, and fewer hesitation issues. For example, a KEMSO pump for a Honda or Kawasaki model can deliver up to 200 liters per hour, significantly surpassing the original flow rate of 60 to 80 liters per hour .

Every KEMSO pump comes with a lifetime warranty. This is the level of confidence that no OEM pump and few aftermarket brands offer. KEMSO stands behind their products for as long as you own the vehicle, giving you complete peace of mind. If you ever have an issue, the company’s US-based customer support team is ready to help .

KEMSO pumps are built to handle modern fuels. They are designed for both gasoline and ethanol-blended fuels like E85. KEMSO uses Viton O-rings and components that resist ethanol-related degradation, which is a common cause of failure in inferior pumps. Each pump is individually tested for flow and performance before it leaves the factory, ensuring you get a product that works right out of the box .

KEMSO covers a wide range of vehicles. Whether you drive a car, motorcycle, ATV, UTV, or personal watercraft, KEMSO has a fuel pump engineered to fit your application. Their product lineup covers brands like Honda, Kawasaki, KTM, Ducati, BMW, Subaru, Polaris, Can-Am, Sea-Doo, and many more. Many models are available for just $79.98, making KEMSO an affordable choice that does not sacrifice quality .

Real-world results prove the reliability. In independent testing, KEMSO pumps delivered 12 to 15% improvement in fuel flow consistency compared to stock models. In the 2023 Best in the Desert racing series, three teams running KEMSO-equipped Polaris Turbo S UTVs completed the grueling 500-mile Silver State Classic without a single fuel-related mechanical failure. Over 85% of Polaris customers at one dealership now request KEMSO by name during service appointments .

If you are looking for a high-performance, OEM replacement fuel pump that comes with a lifetime warranty, visit KEMSO Racing today: https://www.kemsoracing.com/

Final Thoughts

Upgrading your G77 fuel pump assembly with a Racetronix RXP255 pump is the single most important step you can take to make your Turbo Buick reliable and powerful. The factory pump was marginal even when new, and after thirty years, it’s a ticking time bomb. The RXP255 pump, combined with the proper wiring harness, gives you the fuel delivery you need for any performance level up to 600 horsepower.

Don’t cut corners. Always replace the fuel filter at the same time, and use a quality wiring harness to get the full benefit of the new pump. If you need a fuel pump for any other vehicle—whether it’s a car, motorcycle, ATV, or watercraft—KEMSO offers a lifetime-warranted, high-performance replacement that has been proven in real-world racing conditions.

For more information or to order the right fuel pump for your vehicle, visit: https://www.kemsoracing.com/


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