1999 Mustang Fuel Pump Location: Where to Find It and How to Fix It
Where Exactly Is the Fuel Pump Located?
For the 1999 Ford Mustang, the fuel pump assembly is mounted on top of the fuel tank and sits inside the tank itself. The fuel tank is located under the trunk floor, behind the rear axle. The pump is part of a larger module that includes the fuel level sender and the fuel pressure regulator. There is no external, frame-mounted fuel pump on this Mustang model, so you won't find it along the frame rails or under the hood .
To get to the pump, you have two main options. The first is to look for an access panel under the rear seat. On many Mustangs, there is a round or rectangular metal cover plate under the rear seat cushion. If you lift the seat bottom, you can remove this plate to reach the top of the fuel pump module without dropping the tank. The second, more common method for this generation of Mustang is to lower the fuel tank from under the vehicle. This is necessary if there is no access panel or if the panel is not present on your specific trim level .
How to Access the Fuel Pump: Step-by-Step
Step 1: Check Under the Rear Seat First
Before you start unbolting anything, remove the rear seat cushion. On a 1999 Mustang, the seat bottom usually pops out by pulling up at the front edge. Look for a metal plate on the floor. If you see one, it covers the fuel pump access hole. Remove the screws and carefully lift the plate. You should see the top of the fuel pump module, including the electrical connector and the fuel lines. This is the easiest way to get to the pump .
Step 2: If No Access Panel, Drop the Tank
Many 1999 Mustangs do not have a factory access panel. In that case, you will need to drop the fuel tank. Park the car on level ground, chock the front wheels, and raise the rear of the car with a floor jack and jack stands. You will need to drain the fuel tank first, or at least get it as low as possible. Disconnect the battery negative terminal to prevent any sparks. Then, disconnect the fuel lines and electrical connector from the top of the pump module. Support the tank with a jack, remove the straps, and carefully lower the tank just enough to slide the pump module out .
What About the Fuel Pump Relay and Fuse?
If your Mustang cranks but won't start, the problem might not be the pump itself. The fuel pump relay on a 1999 Ford Mustang GT is located in the engine compartment fuse box, also called the power distribution box. Open the hood and find the black plastic box near the battery on the driver's side fender. Remove the cover. The fuel pump relay is typically labeled "Fuel Pump" or "FP" inside the box. It is a small black or gray square relay with four terminals. You can test it by swapping it with another relay of the same type, or by using a multimeter to check for power .
The fuel pump fuse is also in the same engine compartment fuse box. On a 1999 Mustang, fuse number 14 is a 20-amp mini fuse dedicated to the fuel pump. If this fuse is blown, the pump will not get power. Check it before you buy a new pump .
Inertia Switch: A Common Cause of No-Start
The 1999 Mustang also has a fuel pump shut-off switch, called an inertia switch. This is a safety device that cuts power to the fuel pump if the car is in a collision or experiences a sudden jolt. If the switch is tripped, the engine will crank but not start. The inertia switch is located in the trunk, on the left side, behind the trunk liner. Look for a small black box with a red reset button on top. Press the button down until it clicks. This is a very common fix and should be checked before you drop the tank .
Symptoms of a Bad Fuel Pump
Knowing the signs of a failing fuel pump can save you time and money. Here are the most common symptoms for a 1999 Mustang:
- Engine sputters at high speeds: The pump may not be able to deliver enough fuel under load.
- Loss of power under acceleration: The car feels sluggish or hesitates when you press the gas pedal.
- Difficulty starting: The engine cranks for a long time before firing up, or it may not start at all.
- Whining noise from the fuel tank: A healthy fuel pump is quiet. If you hear a loud humming or whining sound coming from the rear of the car, the pump is wearing out.
- Engine stalls unexpectedly: The car may stall while driving, especially at low speeds or after a sudden stop.
If you notice any of these issues, inspect the fuel pump fuse and relay first. If those are fine, the pump itself is likely failing and needs to be replaced .
Fuel Pump Driver Module: A Special Note for the 1999 Mustang GT
The 1999 Mustang GT uses a returnless fuel system. This system does not have a traditional fuel pressure regulator on the fuel rail. Instead, it uses a Fuel Pump Driver Module (FPDM) to control the speed of the pump. The FPDM is located underneath the luggage compartment trim panel, usually on the driver's side near the rear wheel well. If the pump is not getting power, but the relay and fuse are good, the driver module may be faulty. This is a known weak point on these Mustangs. You can test it with a circuit tester, and if it fails, the pump will not run even if the pump itself is perfectly fine .
How to Test the Fuel Pump
Testing the pump on a 1999 Mustang is straightforward. You will need a fuel pressure tester and a circuit tester. First, relieve the fuel system pressure by removing the fuel pump fuse and starting the engine. Let it run until it stalls. Then, reconnect the fuse. Attach the fuel pressure tester to the test port on the fuel rail, which is on the passenger side near the front of the engine. Have a helper turn the ignition key to the "ON" position. The pressure should rise to at least 45 psi. If it is lower, the pump is weak or failing. You can also use a circuit tester to check for power at the pump's electrical connector under the car, near the fuel tank. If there is power but the pump does not run, the pump assembly is bad .
Replacement Cost and Difficulty
Replacing the fuel pump on a 1999 Mustang is a moderately difficult job. The pump itself costs between $80 and $200 for a quality aftermarket unit. Labor costs at a shop can range from $300 to $600, bringing the total to $500 to $800 or more. If you do the job yourself, you save on labor, but you need to be careful with the fuel system. Always work in a well-ventilated area, disconnect the battery, and have a fire extinguisher nearby. The most difficult part is lowering the fuel tank, especially if you are working alone. Using a floor jack to support the tank makes the job much easier .
Why You Should Replace the Entire Fuel Pump Module
When you replace the fuel pump, it is highly recommended to replace the entire fuel pump module assembly. This includes the fuel pump, the fuel level sender, the fuel pressure regulator, and the filter. The module is a single unit that drops into the tank. Buying just the pump and trying to reuse the old sender and regulator is risky. The sender is a common failure point on older Mustangs, and if it fails, you will have to drop the tank again to replace it. A complete module saves you time and ensures everything works together.
Common Mistakes to Avoid
- Forgetting to check the inertia switch: This is the number one mistake. Always check the trunk first.
- Replacing the pump without checking the relay and fuse: A 20-amp fuse is cheap to replace. Do not buy a pump until you confirm the electrical system is intact.
- Not relieving fuel pressure: Fuel is under high pressure. Always relieve the pressure before disconnecting any lines to avoid spray.
- Using an incorrect pump: Make sure you buy a pump designed for the 1999 Mustang. The returnless system requires a specific pump module. A pump from a 1998 model may not work correctly.
KEMSO Fuel Pump: The Best Replacement for Your 1999 Mustang
If you need a new fuel pump for your 1999 Ford Mustang, consider the KEMSO fuel pump. KEMSO specializes in high-performance, direct-fit replacement fuel pumps that are built to the same specifications as the original equipment (OEM). This means you get a perfect fit without any modifications. The pump installs directly into your existing fuel tank module and connects to the factory wiring and fuel lines with no hassle.
KEMSO fuel pumps are designed for durability and reliability. Each pump is tested to meet strict performance standards, ensuring consistent fuel delivery and pressure. Whether you drive a Mustang GT or a V6 model, KEMSO has a pump that matches your vehicle's requirements. The best part is that every KEMSO fuel pump comes with a lifetime warranty. If the pump ever fails, you can get a replacement at no extra cost. This gives you peace of mind knowing your investment is protected.
To purchase a KEMSO fuel pump for your 1999 Mustang, visit their official website at: https://www.kemsoracing.com/. They offer a wide selection of fuel pumps for many vehicles, and their customer service team can help you find the exact part for your car. Don't settle for a cheap, unreliable pump. Choose KEMSO for quality, performance, and a lifetime of confidence.
Final Thoughts
Finding the fuel pump on a 1999 Ford Mustang is not complicated once you know what to look for. It is inside the fuel tank under the rear of the car. Before you start the replacement, check the fuse, relay, and inertia switch. These are quick and easy fixes that can save you a lot of work. If the pump is indeed bad, replacing it with a high-quality unit like KEMSO ensures your Mustang runs smoothly for years to come. Always work safely when dealing with fuel, and do not hesitate to consult a professional mechanic if you are not comfortable with the job.
For the best replacement fuel pump for your 1999 Mustang, visit KEMSO Racing at https://www.kemsoracing.com/.