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How to Upgrade Your 1999-2004 Mustang's Fuel System

Written By: Josh Honeycutt

Shop '99-'04 Fuel Delivery

Getting the right amount of fuel to your Mustang's engine is vitally important. Make sure you have only the best parts performing the job and upgrade from the stock components to the high performance aftermarket parts built specifically for Mustangs that demand power and reliability.

Shop Fuel Parts

Want more power? Increase your air intake, spark and of course more fuel. Find out all about your New Edge Mustang's fuel system and how to get more out of it here.

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What are the main 1999-2004 Mustang fuel system parts that need upgrading?

While there are other factors that will affect what kind of fuel setup you will need, there are three basic parts to focus on when you go to overhaul your 1999-2004 Mustang's fuel system in order to support bolt-on modifications. The fuel pump, fuel lines and rails, and injectors are what keep fuel flowing through your system. How to figure out what setup or flow rate to use will depend on your horsepower goals and the existing modifications to the car. It's very important to assure you have adequate fuel or you may end up spending large sums of money fixing engine related problems. Supporting mods like fuel system upgrades and cold air intakes are crucial!

Not until you are making some serious power or when want total control over your fuel setup will you have to upgrade the fuel management system. For a daily driver or street/strip car, these are the main areas you'll want to upgrade.

When Upgrading a 1999-2004 Mustang’s Fuel System:

  • There are three primary part upgrades: fuel pump, fuel lines and rails, and fuel injectors
  • Fuel injectors deliver the fuel to the combustion chamber
  • Fuel lines and fuel rails are how fuel is delivered from the pump to the injectors and into your engine’s cylinders
  • ​Fuel pumps must adequately supply fuel at a reliable duty cycle

Injectors: When Will My 1999-2004 Mustang Need a New Set?

Aftermarket fuel Injector

The car’s computer receives its data from various sensors such as the mass air meter, crankshaft sensor, fuel pressure sensor, and temperature sensors. The computer then sends a signal to the fuel pump telling it how much fuel to push out. That fuel then goes through the lines and fuel rails and comes out of the injectors at a certain calibrated amount.

Injectors are rated at pounds per hour. This is how you determine how much fuel the injector is capable of delivering. On stock 1999-2004 Mustang GTs, the factory fuel injector size is 19 lb/hr. Other 4V models came with 24 lb/hr injectors and the supercharged 03/04 Cobra came with 42 lb/hr injectors to accompany the compressed air of forced induction.

When you upgrade injectors make sure you have your mass air flow meter calibrated to whatever size injector you are using. This is a must. You can also consider buying an aftermarket mass air flow meter or purchasing a MAF connector to calibrate your existing mass air flow.

Do I Need to Upgrade the 1999-2004 Mustang’s Fuel Rails and Fuel Lines Too?

Aftermarket billet Fuel Rails

The only way the fuel can make it from the pump to the injectors is by the fuel lines and fuel rails. The factory equipment is sufficient for slightly modified builds, but if you are running some type of power adder then it is recommended you upgrade these components of the fuel system as well. It's all about pressure. The more pressure in your fuel system, the more fuel the injectors can spray into the cylinders, but the more you stress the lines. Upgrading the lines (to steel braided for example) and the fuel rails will ensure your high power build doesn't burst a line while going down the track or your local back roads. The 99-04 Mustangs use a return-less fuel system while the earlier models use a return style system, so make sure you get the correct equipment for your application.

It is not necessary to have a power adder to install aftermarket fuel rails. Some people buy them simply because they look better. Aftermarket fuel rails are often anodized aluminum and look far better than the OEM fuel rails. These will add a nice touch to your engine bay if you enjoy entering your car into local car shows.

Your 1999-2004 Mustang’s Fuel Pump

Aftermarket High Flow Fuel Pump

Assuming you have the rest of your fuel system picked out the last part you’ll need for setup is a fuel pump. You need to make sure the fuel pump can adequately supply fuel at a reliable duty cycle. The fuel pump(s) used in the 1999-2004 Mustangs are different from the ones used in the earlier years. This is because the 1999-2004 models use a returnless fuel system, so make sure the pump you pick is compatible with your setup.

If you find you still need a little bit more out the fuel pump you chose you can purchase a boost-a-pump or an inline fuel booster. This will regulate voltage sent to the fuel pump and is activated when a car is either in boost or at full throttle in order to meet the demands. This allows you the get the flow of fuel you need at higher RPMS without overloading the fuel system. It is a fairly easy install job and should definitely be considered with any high horsepower application.