How to Replace Fuel Injection Lines

Over the last couple of decades, the United States has been trying to keep up with the changes in emissions and fuel efficiency laws due to changes in most modern cars. The 1990 Subaru Justy was the last car sold in the United States to have a carburetor; the following model year, the Subaru Justy was sold with fuel injection.

Fuel injection has been around since the 1950s, and electronic fuel injection was used widely on European cars starting around 1980. Now, every car sold in the United States from dealerships are equipped with a fuel injection system.

Fuel lines are designed to transfer fuel from the fuel tank to the engine. On vehicles older than 1988, the fuel lines were made of steel. These lines were great; however, they would rust over the years, causing particles to form in the fuel. In addition, these steel lines would get very hot in desert climates during the summer and cause the fuel to vapor lock.

Vapor lock is a problem that mostly affects gasoline engines. It occurs when the liquid fuel changes state from a liquid to a gas while fuel is still being pumped to the engine. Vapor lock disrupts the fuel pump and causes the fuel to stop flowing to the fuel management system. This issue occurs only when the fuel pump is inline with the fuel system. Older vehicles have fuel pumps mounted on the side of the engine, creating a suction from the fuel tank and a pressure to the fuel management system.

On vehicles from 1988 to 1995, fuel lines were changed to aluminum and galvanized steel. This prevented the fuel lines from rusting with excessive amounts of moisture in the fuel, but the lines would still cause the fuel to vapor lock. Some of the lines were transferred to rubber liner hoses before they reached the engine compartment.

All vehicles from 1996 till today have plastic lines that are known as fuel injection lines. The plastic, or carbon fiber, does not rust or leave particles in the fuel. The heat exchange rate on plastic lines is higher and the fuel pump is submerged within the fuel in the gas tank to eliminate vapor lock.

The three types of fuel injection lines found in modern vehicles are:

  • Return injection vapor line
  • Supply injection high pressure line
  • Return injection low pressure line

The return injection vapor line collects any fuel that bypassed the combustion chamber and exited the engine. This vapor line sends the raw emissions to a charcoal canister to collect the hydrocarbons and sulfur in the vapor.

The supply injection high pressure line transfers fuel from the fuel tank to the injection rail. These fuel lines are designed to handle mass amounts of pressure. Most modern vehicles today produce anywhere from 60 psi (pounds per square inch) to 125 psi. The fuel injection lines are designed to hold up to 750 psi at various ambient temperatures.

The fuel injection system uses about 60% of the fuel transferred from the fuel tank to the fuel rail. The return injection low pressure line sends the 40% of fuel unused back to the fuel tank. The fuel from the high pressure line is cool around 50 degrees to 110 degrees. The fuel from the low pressure line is warmer around 125 degrees to 200 degrees before it reaches the fuel tank.

Part 1 of 8: Understand engine performance

Engine performance works best with fuel at lower temperatures. The atoms of fuel will separate father apart from each other when the temperature rises. This causes the displacement of fuel to take over a larger area. When the fuel is displaced over a larger area and is the same amount of fuel atomized, when mixed with oxygen, the energy spent will be less. This causes the engine to have hotter temperatures than normal. The computer senses this situation and demands the injectors to spray more fuel into the combustion chamber causing a larger fuel consumption. However, when the fuel is cool,the atoms are close together and take up displaced area allowing the power band to be higher in the combustion chamber.

  • Note: When the fuel gauge reads less than a 1/2 tank, the fuel trend is consumed faster. To prevent this, fuel up the fuel tank when the gauge reads at 1/2 tank. This will keep the fuel cooler and make the engine perform more efficiently.

Engine light codes related to the fuel hose on vehicles with computers

Part 2 of 8: Prepare to replace the fuel injection lines

Replacing or updating fuel injection lines from the fuel tank to the fuel injection rail can be frustrating and time consuming. Having all of the necessary tools and materials prior to starting the work will allow you to get the job done more efficiently.

Materials Needed

Step 1: Park your vehicle. Make sure that the transmission is in park mode (for automatics) or in 1st gear (for manuals). Park your vehicle on a flat, hard surface.

Step 2: Secure the wheels. Place wheel chocks around the tires that will remain on the ground. In this case, place the wheel chocks around the front tires since the rear of the vehicle will be lifted up.

Engage the parking brake to the lock the rear tires from moving.

Step 3: Raise the vehicle. Using a floor jack that is recommended for the weight of the vehicle, lift the vehicle at its specified jacking points until the wheels are completely off the ground.

  • Note: It is always best to follow the recommendations given in the owner’s manual of your vehicle and use the jack at the proper jacking points for your vehicle.

Step 4: Place the jack stands. The jack stands should go under the jacking point locations. Then lower the vehicle onto the jack stands.

  • Tip: For most modern cars, the jacking points for jack stands will be on the pinch weld just under the doors along the bottom of the car.

Step 5: Install a nine volt battery saver into your cigarette lighter. This will keep your computer live and keep your setting current in the vehicle. If you do not have a nine volt battery saver, you can skip this step.

Step 6: Disconnect the battery. Open the vehicle’s hood to disconnect your battery. Take the ground cable off the battery’s negative post, disabling the power to the ignition system and fuel system.

Part 3 of 8: Check the condition of the fuel injection lines

Step 1: Check for leakage in the engine compartment. Using a flashlight and a combustible gas detector, check for any leaking fuel in the engine compartment.

Step 2: Check for leakage in the injection lines. Use a creeper to slide under your vehicle and check for any fuel leaking on the supply, return, or vapor injection lines.

Part 4 of 8: Remove the fuel injection lines

Step 1: Remove the fuel injection line. Use a fuel hose quick disconnect tool and remove the fuel injection line from the fuel rail behind the engine along the firewall.

Step 2: Remove the fuel injection line. Slide under the vehicle and remove the fuel injection line from the vehicle. This line may be held up by rubber grommets.

  • Note: Be careful when removing plastic fuel injection lines as they may break easily.

Step 3: Remove the fuel line from the fuel filter. Use a quick disconnect tool and remove the fuel line from the fuel filter.

  • Note: Not all vehicles have inline fuel filters. Most of the newer systems have the filter in the fuel tank attached to the fuel pump.

Step 4: Get a transmission jack or similar jack. Place the jack under the fuel tank. Remove the fuel tank straps.

Step 5: Open the fuel neck door. Remove the mounting bolts to the fuel filler neck.

Step 6: Remove the plastic fuel hose from the fuel pump. Lower the fuel tank far enough to remove the plastic fuel hose.

Use a quick disconnect tool to remove the fuel line from the fuel pump. Place a drip pan under the fuel tank and remove the fuel hose from the fuel pump.

  • Tip: You may have to disconnect the other fuel lines to get to the fuel line you are replacing.

  • Note: If you are removing all three lines, then you will need to remove the vapor line from the charcoal canister and the return line from the fuel tank using a quick disconnect tool.

Part 5 of 8: Install the new fuel injection lines

Step 1: Install the new fuel injection line. Get the new fuel injection line and snap the quick disconnect together onto the fuel pump, located on the fuel tank.

  • Note: If you are installing all three injection lines, then you will need to install the vapor line to the charcoal canister and the return line to the fuel tank by snapping the quick disconnect together.

Step 2: Raise up the fuel tank. Align the fuel filler neck so it can be mounted.

Step 3: Open the fuel neck door. Install the mounting bolts to the fuel filler neck. Tighten the bolts hand-tight and then 1/8 turn.

Step 4: Hook up the fuel tank straps. Put loctite onto the threads of the mounting bolts. Tighten the bolts up hand-tight and then 1/8 turn to secure the straps.

Step 5: Complete the process. Remove the transmission jack from under the vehicle. Snap the quick disconnect on the fuel injection line to the fuel rail behind the engine along the firewall.

Part 6 of 8: Check for leaks

Step 1: Connect the battery. Open the vehicle’s hood. Reconnect the ground cable back onto the battery’s negative post. Remove the nine volt battery saver from the cigarette lighter.

Tighten the battery clamp up tight to ensure that the connection is good.

  • Note: If you did not use a nine volt battery saver, you will have to reset all of the settings in your vehicle, like your radio, electric seats, and electric mirrors.

Step 2: Turn the ignition key on. Listen for the fuel pump to activate. Turn off the ignition after the fuel pump stops making noise.

  • Note: You will need to cycle the ignition key on and off 3 to 4 time to ensure all the fuel lines are full of fuel.

Step 3: Check for leaks. Use a combustible gas detector and check all of the connections for any leaks. Sniff the air for any fuel odors.

Part 7 of 8: Lower the vehicle

Step 1: Clear up your tools. Collect all tools and your creeper and place them out of the way.

Step 2: Raise the vehicle. Using a floor jack that is recommended for the weight of the vehicle, lift under the vehicle at its specified jacking points until the wheels are completely off the ground.

Step 3: Remove the jack stands. Remove the jack stands and keep them far away from the vehicle.

Step 4: Lower the vehicle. Lower the vehicle to where all four wheels are on the ground. Pull out the jack and put it aside. Remove the wheel chocks from the rear wheels and put them aside.

Part 8 of 8: Test drive the vehicle

Step 1: Drive the vehicle around the block. During the test, go over different bumps allowing the fuel to slosh around inside the fuel injection lines.

Step 2: Check for any dashboard warning lights. Monitor the dash for the fuel level and for any engine light to appear.

If your engine light comes on after replacing the fuel injection lines, then there may be further diagnosis of the fuel system or a possible electrical issue within the fuel system.

If the problem persists, get a certified technician from YourMechanic to inspect the fuel injection lines and diagnose the problem.


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